Q: What are the basic components of an antweight robot? Could you show me in a diagram or picture how they are put together?

A: The basic components for a combat robot are pretty much the same for all weight classes. I have a diagram in the section that shows the components and how they connect. It's about half-way down the page.

A: I always encourage first-time builders to keep their robot design simple. You'll have enough problems to sort out without adding an active weapon into the mix. A well-built wedge or scoop is always competitive.

I can't tell you if a trip to England for an antweight tournament would be worth your while, but I can tell you that I've travelled greater distances for a good robot fight. You'll either love it or hate it, and the only way to find out is to go.

I have the 75 MHz Pico receiver right now but I am going to upgrade to 2.4 GHz. Do you know of any ways to fit the Spektrum BR6000 receiver into the Inertia Labs chassis and still be able to drive inverted? Can you strip the BR6000 of any excess plastic so that it can fit?

A: There isn't a lot of space inside the Inertia Labs chassis. The guys at Dimension Engineering have some photos of the standard set-up with the GWS receiver. They compare fitting the components in place to a game of Tetris.

You're not going top save much room by modifying the case of the BR6000. The problem isn't the thickness, it's the rather large footprint. Unless you come up with some creative solution to reduce the footprint of the battery (custom NiMHd pack?) I don't see a way to cram everything into the chassis and get the lid on.

Another question: I have a Sabertooth ESC. Is it possible to connect this ESC to a 7.2 volt battery on the brushless system without an enternal ESC battery?

A: Hi, Anthony. I can't recommend that a beginner build a Full-Body Spinner for their first robot. It is possible to make an effective FBS, but there are very few that are successful and a whole lot of them that are not.

The spinning shell must carry as much weight as possible and be very well supported. When the weapon makes contact there will be as much force placed on your robot as is transmitted to your opponent. It's likely that your 'bot will fly off in an unpredictable direction and bounce off several walls in a small arena. The 'bot must be very well constructed to survive this sort of treatment. Just bolting a mixing bowl to the shaft of a motor is not going to be nearly sturdy enough.

If this is an insect-class 'bot you've got another problem. Insect arenas are very small and you will have very little time to spin your weapon up to an effective speed before your opponent is on top of you. You'll need to be very good at dodging their first attack if you're going to survive long enough to stay in the match.

There are several previous Q&A about spinners in the archive that should be helpful to you. I'd also suggest reading the for my answer to the question about what type of weapon is best.

I'm not sure I understand the ESC question. If you're asking if you can hook the Sabertooth up to the same battery that powers the brushless ESC for the weapon -- yes, you can do that. Just make sure the battery has enough capacity to power both systems. There is a wiring diagram in the that shows how everything goes together.

Q: Dear Aaron, it's Anthony again. I decided to build an antweight horizontal disc spinner instead of an FBS. How do I make it effective? Is the new polycarbonate VDD weapon gear box sturdy anough for competition? If it isn't, will I need a tougher shaft then the kit shaft from the Robot Marketplace?

A: We have LOTS of information on spinner weapons and how to make them effective in the archive. Browse around in there. Horizontal spinners are a bit of a challenge because they 'kick' off to one side on impact just about as far as they 'kick' the opponent the other direction. Not very popular for that reason - sure you want to build one of those?

The VDD weapon parts are all combat tested and will perform well.

Q: How exactly does 'Micro Nightmare's main 14.8 volt battery power both the Hacker brushless system and the SozBots speed controler at the same time? Can the same be done with the Scorpion HX? I'm confused.

A: I pointed you to the wiring diagram in the last time, Anthony. That diagram shows how to wire a weapon ESC and a drive ESC to a single battery pack. They are wired in parallel: connect both '+' inputs on the ESCs to the '+' battery terminal, and both '-' inputs to the '-' battery terminal. That will work just fine with your Scorpion HX.

A: This question keeps popping up and I keep answering it.

A: Sure -- you can use a nano servo to operate the Lego pneumatics switch and control the system. However, the Lego pneumatics components do not provide enough power to be very useful in even an insect class combat robot. CSSOH'S Lego Pneumatics Page has many examples of Lego pneumatics construction and a primer on Lego pneumatics. I can't recommend a particularly good place to purchase the sets, other than the usual places like amazon.com.

Q: I recently asked about Lego pneumatics and you said they didn't provide enough power for an antweight fliper. Well, I searched and found that the larger Lego pump can supply enough force to lift about 3 pounds. How much more do I need for an antweight flipper?

A: Mark J. here: Power is the product of two components: force and speed. The Inertia Labs micro pneumatic system delivers 16 pounds of force and delivers it very quickly thanks to a high-flow valve and pressurized storage tank. The Lego system operating off of an electric air pump is designed for slow and safe actuation; it takes way too long to develop force and move it over enough distance to make an effective flipper. The best you'd get is a slow and very gentle lifting action -- absolutely not a flipper.

A: Scroll down a little to the 'Grabby' question for a discussion on antweight crushers. Nobody has built a successful antweight crusher yet, and it may not be possible. It certainly wouldn't be easy!

A: Sorry, no off-the-shelf CO₂ systems that small. Inertia Labs made a small low-pressure air pneumatic system for insect-class robots, but they are no longer produced.

A: Mark J. here: let me take this one, Aaron.

It's really difficult to discuss just one part of a weapon system. A motor that would work well for one clamper design would be completely unsuitable in another. That said, the Tamiya 72001 is not really 'combat quality'. The gearbox housing and gears are plastic and the output shaft is poorly supported and of too small a diameter to properly fasten a clamp arm. You'd be much better off with a more robust gearmotor like the Beetle B231.

A: The photo of Grabby at the Inertia Labs website shows a single standard-size servo connected to twin pushrods that activate the claw mechanism -- pulling back to close the jaw and pushing forward to open it. Two pushrods are needed because the ends of the claw mechanism diverge as they move. There is a second 'thin wing' servo attached to an arm apparently used as a SRiMech.

Given the lever advantage, the claw will actuate quickly, but will not have much grabbing force. Certainly not a crusher.

Q: Have "Grabby', 'Lifty', and 'Cutty' competed or are they just examples on the Inertia Labs website?

A: All three robots are credited as being built by The Machine Lab. I'm not sure that they were built as combat robots, and I can find no record of any robots from 'The Machine Lab' in combat competition.

Q: You said that Grabby's design was meant for speed, not force. What design would work for force? What would it take to build an antweight crusher with the Hitec 645-MG servo implementing the design of Grabby? Would the servo supply enough power of would you have to use something else like small hydraulics?

A: Mark J. here: contrasting Grabby to a crusher was a facetious exaggeration. Direct servo-powered clampers can have a large range of travel and little force like Grabby, or you can change the lever pivot point to reduce the range of travel and increase the clamping force. Every time you double the clamping force, you cut the amount of jaw travel in half. By the time you got enough force to do any damage, the jaw travel would be unuseably small.

You could modify the servo for continuous rotation and design an external gearbox to multiply the available force. The problem then becomes that force and speed are a trade-off: more force gives less speed and vice versa. Jaws with significant force and travel would be agonizingly slow.

There is nothing magical about hydraulics; you still have the problem with the inverse relationship between force and speed. If such tiny hydraulic components existed, their only advantage would be that high force can be generated without the need for heavy gearboxes and linkages.

An additional problem with crushers is the enormous stress placed on the chassis of the robot deploying the weapon. A force equal to the force applied to your opponent must be borne by your own chassis. I've seen several would-be crushers that succeeded in ripping themselves apart.

A: Good servo choice. The 645-MG will deliver 38 ounces of lift at the end of a 3.5" arm. That's plenty to give quick and reliable lifts.

A: The kilobot version of 'Mars Attacks' was a thwackbot spinner made to look like a shell spinner. A thwackbot can't move when attacking (unless you have some fancy melty brain electronics) so all it can do for offense is sit and spin. There have been very few successful thwackbots -- judges hate them -- but they are fun to drive.

A: The HXT 12kg (AKA Towerpro MG995) has Futaba splines and is quite inexpensive, but I strongly recommend that you buy something else.

All the reviews I've found say they're junk. They're heavy, poorly made, unreliable, and don't come close to meeting their advertised performance figures. One review thinks they may be the "world's worst servo." I wouldn't modify one of these to throw itself away. Avoid.

A: If you want to keep it simple, try the Hitec HS-775MG servo. It's reasonably priced, has 200 oz/in torque, full metal gears, and easy mounting tabs.

Q: Which will be better for a beetle clamp: the servo you sugested running at 7.2 volts? or a BaneBots 28mm 25:1 gearmotor at 7.2 volts? If I use the BaneBots should I support the shaft?

A: I considered the BaneBots motors before I made my recommendation. The Hitec servo will hold better at a lower amperage draw, is an easier shaped package to mount, and requires no external speed controller. If you use a clamping arm that has some side flex (Lexan, maybe?) and mount close to the output bearing, either the Hitec servo or the BaneBots gearmotor should be OK with no additional shaft support.

Note that the Hitec servo is rated only up to 6 volts. I've never used this servo, but suspect it will be OK at 7.2 volts.

A: Mark J. here: there are several posts on the design of 4-bar lifters in the archive, including a link to design software.

For an antweight the servo output can replace the entire rear (or front) bar of the mechanism to simplify construction. The diagram at right shows one possible configuration.

A: Composite armor is tricky -- you can end up with the worst properties of the individual materials rather than the best. Even if you got the best properties of those three materials you still wouldn't have much. If you have to stick with stuff you find around the house, polypropylene plastic ('PP' in the recycling label) from snap-on lid kitchen storage containers is quite tough and easy to work with. It would be a better choice.

A: I'm not sure what you mean by 'self contained', but there is a discussion on different servo powered lifters in this archive. Search for "using a servo". The simplest approach is to just attach a lifter arm directly to the servo output wheel.

A: The Hitec 645MG is a great servo for an antweight lifter. The Futaba S3305 is comparable: a little lighter and a little less expensive with all metal gears and dual ball bearings.

A: The wheels usually used on the Inertia Labs chassis are the 24mm diameter Ultra-Light wheels. They are a press fit onto the 3mm diameter Sanyo shaft -- no hub needed.

A: Sounds like a good choice. For use in an 8-foot arena, I'd go with the 20:1 gear ratio: 0 to 5.5 MPH top speed in 3.5 feet, and cross the arena in 1.2 seconds. Maximum power draw would be about 2.2 amps per side, well within the Ant 150 capacity. If your arena is larger, consider the 16:1 gearing for a little more speed.

A: Mark J. here: we've never worked with 15-3 (AKA 'Timetal'), but I've looked up it's properties and it appears to be an excellent armor material. Complex metal forming can locally 'work harden' titanium and lead to cracking under later stress; keep the bends simple and you should have no problems.

In aerospace applications, Timetal is re-annealed after forming, 'age hardened' at high temperature, then air cooled. This is the ideal treatment and it will add about 40% to the strength of the finished piece.

A 21 gauge sounds appropriate, but armor performance depends on factors other than just thickness. The size and shape of the piece, mounting method, and support from other chassis elements all count toward performance, but unless you're doing something odd the 21 gauge should be great.

A: Mark J. here: a few thoughts:

• 30K RPM is WAY too fast to spin a rotating blade -- see previous question on blade speed in this archive;
• the drivetrain sounds fine;
• a solid machined titanium antweight chassis is expensive overkill.

Q: What happens if you spin a blade to fast?

A: Like I said, see previous question on blade speed in this archive. Search the page for 'too fast'.

A: Chassis or wheel magnets are left to the discretion of the event organizer. Some allow them, some do not, and some arenas don't have a magnetic floor so it doesn't matter. At least a few builders provide their 'bots with a set of magnet wheels to use where they are allowed and a set of rubber wheels to use elsewhere.

A: Yes. Inertia Labs had an ant named 'KanunDrum' with a internal combustion powered drum. The 'bot was never mentioned on their website. It fought at the Marin Ant Wars in 2004 and 2005. Botrank.com shows 1 win and 3 losses.

Q: How does KanunDrum's weapon work? Does the ICE power the wheels too?

A: The drum is belt driven by a model aircraft internal combustion engine. It looks like a servo is used to engage the belt with an idler wheel. The engine is manually started via an extension of the shaft that sticks out to the left of the 'bot. The wheels are driven by electric motors.

A: See my warnings about overvolting in the . The FA-130RA motors that come with the Tamiya gearbox are particularly vulnerable to melt-down if allowed to overheat. I would not run them higher than 6 volts even with a low enough gearing choice to spin the wheels well before stalling.

A: What is it about an FBS that makes it so attractive to builders? If you take the time to research the combat record of FBS robots you'll find that, as a group, they have a very poor win percentage in any weight class. They are often as dangerous to themselves as to their opponent -- ricochetting off at odd angles and into trouble. I can't recommend building one.

Your design questions all depend on specific information about the dimensions of the shell, the material used, the torque of the motor, and the size of the arena. The Team Run Amok Spinner Spreadsheet for Excel can perform the calculations you'll need to determine the power and gearing requirements for a specific shell design. I have seen direct-drive antweight FBS, but they had small diameter shells and very powerful motors.

Q: How come there are not many full body spinner antweights?

A: Read the answer above: there aren't many ant FBS because ant FBS have a poor win percentage. Most builders want to build something that they think can win.

A: Several reasons:

• No high-pressure pneumatic equipment is available in antweight sizes;
• Antweight 'bots can generally survive repeated flipping without damage;
• Damage/aggression scoring systems don't give credit for flips;

A: 'Hummer' is a beautifully designed and constructed antweight. It is also very successful: 26 wins and 6 losses, seventh in the Botrank historic rankings. 'Pele' is more of a show-off 'bot -- fun to look at and an interesting challenge to drive, but not really competitive: 10 wins and 14 losses.

I don't believe that the Inertia Labs pneumatic parts are available anymore. If you could scrounge enough pieces to put a system together I'm sure you could have some fun with it, but don't expect to win tournaments.

A: I don't like a hinge on a front wedge. The hinge would be a weak point in the wedge mounting, and a hinged wedge can fold back under the robot and lift the wheels of the robot off the floor. If you want the wedge to scrape the floor, you can build a subframe for the wedge and pivot it from the center or rear of the robot, like the scoop mount on Breaker Box.

Small hinging mounts for antweight side skirts can be made from heavy package tape or from small mechanical hinges available from your local hobby shop. The hobby shop will also have special 'hinge tape' used for model aircraft control surfaces. You could also use small metal jewelry box hinges available at craft stores.

A: I don't know of any ready-made wheels that small in diameter with that large a bore. It's time for a trip to your local hobby shop to see what they have. Check slot car wheels and R/C airplane landing gear wheels. You're going to have a hard time finding a small wheel with enough material in the hub to allow enlarging the bore to 6mm.

You've probably figured out that you aren't going to get much speed out of 3/4" diameter wheels on standard ant gearmotors, but I thought I should mention it.

A: Oddly, there seems to be some argument about what 'best' means. To me it means the weapon that gives you the greatest chance of winning. Other builders would rather put on a spectacular display of destruction, even if it means they seldom win a tournament.

We did some research to find out what weapon types win the highest percentage of matches. Overall, robots with passive weapons (wedges, bricks, rammers) win more often than robots with active weapons (spinners, flippers, lifters). However, if you look carefully at all the sub-classes of weapons, it's lifters that do the best. They don't win many matches by knock-out, but they can dominate a battle and make an oponent look weak and ineffective.

Antweight lifters are relatively easy to construct because R/C servos have enough power to function as your lift motor.

Q: I was wondering if I should skip the antweight an go straight to a larger bot? I know it will be more expensive but maybe I can save up. Will I find more or fewer competitions? [pyrobug]

A: Generally, the heavier the 'bot, the harder it is to find a match. In 2007 the number of RFL sanctioned matches by weight class looked like this:

A: Mark J. here: the large scale R/C airplane guys use pneumatic systems to raise and lower landing gear in a realistic, slow manner. Their pneumatic cylinders can produce good force, but the critical ports and valves flow air too slowly for a flipper.

A: The amount of force at the end of a simple arm attached to a servo is:

Example: a servo with 60 oz-in torque with an arm extending four inches from the central axis of the servo will have:

Note that the servo would be able to 'hold' 15 ounces at the end of the arm. It would be able to slowly lift 14 ounces, speed increasing with lessened weight.

A: Mark J. here: as noted in the all the tools you need to evaluate spinner motor performance with specific weapons are in the archives. In particular, the Team Run Amok Spinning Weapon Excel Spreadsheet will detail and graph the performance of a specific motor spinning a specific weapon at a specific gear reduction.

There's an infinite number of combinations of motors and spinner weapon designs. I've provided the tools, you run the numbers. Fair?

P.S. -- You'll need to know the width and thickness of the bar in addition to the length and material.

P.P.S. -- Oh all right: assuming that the bar is 1" wide and 1/4" thick (about 6 ounces), the GWBLM001 2205/15T geared 4:1 will spin it up to about 2500 RPM and 45 joules of energy in 2 seconds. Killer. But seriously, that's the last spinner analysis I'm gonna do!

Buy a couple of those motors -- BaneBots is closing them out at a very good price.

A: I've seen many competitive antweights built around the Tamiya Twin Motor Gearbox. It is inexpensive, sturdy, and provides adequate power for an ant. The main drawback is that it's a little bulky.

A: Mark J. here: It's not even close to being a 'complete kit'. You get a chassis, motors, wire, and wheels. You need to come up with radio gear, an ESC, a battery pack, charger, and some sort of weapon. The machined aluminum chassis is way cool, but not easy to repair if it gets pranged. You might want to order a spare for your pit box. I don't really consider this to be a 'first time' kit.

Q: Were can I get the 'A:1 Complete Antweight Kit' now that Composite Labs shut down?

A: Weak! I hadn't heard that Composite Labs was gone. I had been recommending their kits. They were the manufacturer and only source, so they're gone for good.

It's difficult for me to recommend any of the currently produced antweight kits for a beginner. You're going to spend $300 or $400 and end up with a marginal radio, a low-end battery charger, and a pile of parts with no specific instructions. I'm gonna go back to suggesting that a beginner find an old BattleBots R/C toy on EBay, hack the radio and drive motors, add a wedge, and go beat up some $400 'bots for $50.

A: Way too flimsy. The first spinner you came up against would shred it. Try titanium, and three times that thick.

A: Sure! There are many good antweight lifters powered by servos. See previous posts on selecting an antweight lifter servo and designing 4-bar lifters.

A: Match the cooling fan to your voltage and it'll work, but it's overkill. A pair of them would weigh half a pound -- a big chunk in a three pound robot. Why would you want heavy 60 amp ESCs in an beetle?

A: I won't post information here that could lead an inexperienced builder to injure themselves. See the previous post on flamethrowers for reasons to build something else.

A: Magnetic wheels are extremely effective -- if you happen to be fighting in an arena with a steel floor. I've only seen them used on insect-class bots. See Team Nightmare's beetle page for some good photos of the 2004 beetleweight national champion 'Wallop' with its magnet wheels.

The wheels are simply round rare-earth neodymium magnets with a hole in the center. These can be very expensive, unless you happen to find a suitable set at a surplus outlet.

Don't leave magnet wheels exposed. Put them under your armor or use side guards to keep them from clamping onto steel rails or other vertical structures. It would be embarrassing to end up stuck to a railing. Also, be sure to check with your local event organizer to see if magnet wheels are even allowed!

A: First, find another hobby shop - one that knows something about 'bots. Second, servos make poor 'bot drive trains. Save up your money and buy a real speed controller and drive motors. See the servo discussion for more info.

A: I like to fight big 'bots! The bigger the 'bot the better -- but even tiny 'bots rock.

A: The side-wheel spinner design on Run Away is unique and showy, but a pivot steer 'bot like Run Away would be very difficult to maneuver in a small arena.

A: No. Internal Combustion Engines (ICE) are tempting, but getting them to work well and reliably in combat can be a huge problem. Also, not many insect class competitions allow ICE. Check the rules for your competition before you commit.

A: You could do a lot worse than the components used for the Robot Marketplace Basic Antweight Starter Package, Nick. The Tamiya dual-motor gearbox is quick and tough, and the 56 mm 'sports tires' slide right onto the shafts of the gearbox. The Ant 100 ESC is reliable, but I'd upgrade to the Ant 150 ESC for a weapon control channel that could come in handy on a later 'bot.

Radio and battery/charger are up to you. I use inexpensive NiMHd cells for ants because chargers for them are available and cheap -- but LiPoly cells are lighter. Bolt everything down to a simple flat chassis, add your armor and a sturdy wedge. Keep your first 'bot simple and have fun!

A: Servos are slow! The speed of a typical 'fast' servo modified for continuous rotation is about 60 RPM. With a 2" diameter tire that gives you about 32 feet per minute, or less than 0.4 miles per hour. That's not even a crawl!

It is possible to 'speed mod' a servo by locking the first and third reduction gear clusters together and eliminating the second reduction stage altogether. That will improve the speed by a factor of fifteen or more, but will reduce the torque by the same factor. It will make the motor prone to stall and an early death. It isn't worth the trouble -- don't use servos for drive motors.

The Futaba S3110 is a really tiny servo. The gear train is way too fragile to even consider using it as a drive motor in an antweight. It would be slow, weak, and vulnerable.

A: Mark J. here: I can't figure out why a servo would be your only option, but if you wanna do the servo thing right my choice would be the Hitec HS-5996TG.

• The titanium gears are next to indestructible,
• A beefy 111 oz/in stall torque is un-stallable,
• 60 degrees rotation in 0.10 seconds is nasty quick (for a servo),
• Hardened gear pins and intermediate oilite bushings with ball bearings on the output shaft will take serious punishment, and
• The coreless motor shaves the weight down to 63 grams.

Q: Is there a good servo to power a 'bot for less than $40?

A: It's funny how fast a price limit gets set when somebody finds out what 'absolute best' actually costs.

I really don't want to encourage you to build a servo-powered 'bot - they're really slow! For less than the $80 you're willing to pay for a pair of servos you can buy a Tamaya dual-motor gearbox and a good speed controller that will run rings around any servo-bot. Reconsider?

A: 'Cheap' and 'robot combat' really don't go well together. You're gonna spend your time and effort to build something that's going to let you down in battle. Why bother?

If you insist: buy a Futaba '2DR' 2-channel AM R/C setup. It comes with a transmitter, a receiver, two servos, crystals, mounting hardware, and a battery holder for about $40. Hack the two servos for continuous rotation. Find the centers on two plastic mayonnaise jar lids and mount them to the servo horns with self-tapping screws that come with the radio -- instant wheels. Stretch a wide rubber band around the outside of each jar lid for tires. Foam tape the receiver, battery holder, and servos to one of those free AOL CDs that come in the mail. Insert 4 AA cells in the battery holder and 8 more in the transmitter.

Congratulations, you've just built the world's cheapest scratch antweight. Now, throw it away before you embarrass yourself.

Q: In a earlier post you mentioned the complete Futaba 2DR AM R/C set for around $40. Where can I buy one?

A: Futaba 2DR at Tower Hobbies. This is a two-channel AM system. Check with your local event rules to make sure they allow AM radios for the weapon type and weight class you plan to build. FM radios are more expensive for a reason: they work better.

A: Rat trap - $1.79.

Q: How can I make the rat trap into a weapon?

A: Don't be too anxious; the rat trap is cheap but I'm not saying it's good. Set the trap and drive toward your opponent -- you get one shot. Check legality with your local event organizer and watch your fingers!

Q: I'm having trouble with my rat trap weapon. Every time I bump something the trap snaps shut. Is there a way to make it less sensitive?

A: Examine the way the trap latches to the trip plate. The bar is held by a very narrow dimple of bent metal. Bend the dimple to make it deeper, and reshape it to hold the bar more firmly.

My dad's antweight has a tiny servo that latches the trap shut 'til he releases it -- but that adds too much expense for it to qualify as the 'cheapest active weapon'.

Q: How did you turn Rat Amok into a flipper 'bot?

A: You must have seen the 'Rat Amok' video. Rat Amok isn't designed to be a flipper, but if an opponent climbs far enough on top they can be thrown forcibly upward then the trap is released. Other times, the trap ejects the opponent out the front of the trap at high speed and Rat Amok may flip over backward in reaction (she drives fine upside-down). Only occasionally does the trap actually 'catch' a part of the other 'bot. Teeth or a rubber 'gripper' added to the trap bar would modify the effect of the impact.

Q: What was the total cost of Rat Amok? What servos did it have?

A: Mark J. here: Let's see --

• Rat trap - $1.79
• Futaba T6XAPS R/C system - $229.95
• 2 Futaba S3004 ball bearing servos - $0.00 (came with R/C system)
• Cirrus 'nano' servo trap release - $29.95
• 5 700 mAH NiMHd cells - $9.95
• 2 front wheels from Tamiya R/C dune buggy - $7.95
• Dollar Store knife for front blade - $1.00
• Polypropylene cheese box from thrift store - $0.50
• Assorted hardware - $2.58

A: Servos are way too slow to directly power a flipper. I suppose you could use a servo converted to continuous rotation as a winch to wind a spring for a flipper, but that's too complicated to write about here.

You can use a servo to power a small lifter for an insect-class 'bot. You can simply connect an arm directly to the servo output wheel, but you'll have more interesting leverage options if you connect the servo to the lifter with either a rod link or a full 4-bar linkage. Search down the page for "4-bar" for tips. Your local hobby shop will have everything you need.

Q: What should I look for in a servo that's gonna power an antweight lifter? How powerful should it be (in/oz)? Are there any successful antweight lifters?

A: Mark J. here: I've looked around at ant lifters and the only things their servos have in common is high torque. The drive gears are usually well protected so metal gears are not needed. Speed isn't really an issue either. You don't need to spend a lot of money here.

Assuming that you're using the servo on one end of a simple lifter arm, you need to have enough power at the end of the arm to lift 16 ounces. Example: if you have a 3 inch long lifting arm, you need 3 in. X 16 oz. = 48 in/oz torque, plus about 25% to keep it from stalling. More torque will lift faster. There are other factors to consider, but that will get you in the ballpark.

My favorite (and very successful) antweight lifter is Adam Conus' Mission Control. Technically it's a clamp-bot since it has a second servo on the lift arm that clamps the other 'bot in place. Adam uses a Hitec high-torque standard servo with 76 in/oz of torque for the lifter and a Hitec mini servo for the clamp.

Q: In an earlier post you mentioned that a servo could be used as a winch to wind a spring for an antweight flipper weapon. How would you put that all together?

A: I also mentioned in that post that the winch was too complicated to write about here. I guess you didn't believe me!

The servo must be converted to continuous rotation and a small bobbin added to wind in string. The string passes around a pulley and attaches to the front edge of a mousetrap bar to pull it down. The complicated part is disengaging the bobbin so that it will spin free when the trap is released and re-engage when you're ready to reset the flipper. That requires a second servo and a better drawing than I can make. A pneumatic flipper would be less trouble.

A: Mark J. here: Chris Sherwood has been building robots in England for a long time. He was able to build his 150-gram pneumatic 'bot out of odd bits and pieces because of his extensive building experience. You can find pictures of 'Flipper': here. I don't believe his design would be legal (or competitive) in the U.S. under current RFL rules.

Very briefly, Chris uses a plastic egg for an air pressure reservoir and syringes for pneumatic cylinders. The system fires the 3-way pneumatic valve when a robot hits the microswitch on the flipper. Take a look at the Inertia Labs Micro Pneumatics FAQ and read the Micro Pneumatics PDF for info on building a similar system that would be safe and legal.

You might also be interested in using Lego Mindstorm Pneumatics parts for a low-budget insect flipper 'bot.

A: If this is your first 'bot, keep it simple. An antweight wedge would be a great choice for a first scratch-built 'bot. Search down the page for an antweight parts list and lots of tips. You can get all the supplies you need at Robot Marketplace. I just counted, and that's the 18th plug for Robot Marketplace. Doesn't anybody read the old questions?

A: That's not much of a description. The motor must fit in with all the design elements of the 'bot and work with them as a whole. What's your weapon? How large is the arena you'll be fighting in? What is the arena layout? Is speed more important to you than pushing power? What's your budget? Two wheel drive? Four wheel drive? Wheel size? Are you willing to make custom hubs, or do you want off-the-shelf parts only? Do you plan to use a lithium battery, or NiMH? How much weight allowance is available for the motors?

You can search down the page for 'fairyweight wedge' for a general recommendation of a motor that would make a good starting point for a 'bot.

A: You really have to make sure your wheels are securely fastened to the gearbox shaft. Having a wheel fall off is pretty much the most embarrassing thing that can happen in combat, so I really can't advise scrimping on hubs. Robot Marketplace has nice 3mm aluminum hubs to fit Lite Flights and other wheels for about $5 each. If you're really cheap, Tamaya wheels come with 3mm press-on plastic hubs for both round and hex shafts -- but if they shatter or just fall off, don't say I didn't warn you.

A: We used car-style steering on our heavyweight 'bot 'Run Amok'. Car steering is better than tank-style 'differential' steering at holding a straight line course and at making smooth turns, but tank steering gives much greater maneuverability in tight spaces. Car steering can work in a wedge or rammer in any weight class, but it certainly isn't popular.

P.S. - Alex Udanis wrote to tell me he thinks car steering bites. He didn't actually say 'bites', but I don't want to use the word he picked.

A: Mark J. here: just like there are different alloys of metals, there are lots of types of fiberglass. The type of resin used is very important to the properties the material as a whole exhibits. Some resins are hard, but brittle. Others are more resilient. See the earlier post on garolite in the archive.

A: No 'product' needed -- just solder three ESC wires to each output pin on the battery connector plug. I use Deans Power Plugs for ant and beetle connectors, but any good R/C hobby power connector is fine. Buy them at your local hobby shop. Don't use automotive connectors (bullet connectors) -- they give trouble in robots.

A: Neither SozBots nor RFL rules specify a maximum size for U.S. antweights or fairyweights. It's the British '150 gram' antweights that must fit in a 4" cube.

A: Tech question, Mark J. here: Outrunner style motors are a problem to mount because the entire outside 'can' rotates. Some outrunners (like the AXI) have a shaft that runs thru the rear mounting plate that makes for a simple mount. Others (like the Park) don't have a shaft in the rear and you have to get creative.

Take a look at Team Basenji's antweight 'Bitsy Blade' at the Robot Riots 5 photos page. It's an ant vertical spinner with an outrunner. They simply mounted the rear motor plate to the chassis and left the rest of the motor and pulley drive dangling in the air! It isn't good engineering practice, but it works for them. A better solution would be to add a support to the motor shaft as close to the weapon pulley as possible with a bearing on a strong support anchored to the chassis -- kinda the same as their weapon support.

Technical question, Mark J. here:

• Robotmarketplace.com claims that the Park 370 Outrunner has "awesome torque" and that "in most circumstances" the motor can be used direct drive for an antweight weapon. I'm not able to find actual torque figures for the motor to back up those claims.
• The power needed to spin a 7 oz. bar depends on the length of the bar. A short bar has less rotational mass than a longer bar and will require less torque to 'spin up'.
• A spinning bar weapon needs to spin slowly enough for the bar end to grab and catch your opponent. The Park 370 Outrunner has a no-load speed close to 10,000 RPM at 7.2 volts! That's much too fast to spin a bar weapon.

A: Unless you're running a very powerful weapon motor or a very small drum, you will need some gear reduction to spin the weapon up properly. The Team Run Amok Spinning Weapon Excel Spreadsheet can give you some help in designing your weapon For a reasonable motor and a mid-sized drum, try a belt drive with about a 3:1 reduction for a starting point.

A: The number of flips you get is dependent on the size of your air storage tank, the volume of your pneumatic actuator, and the pressure of the air in your system. You can design in as many flips as you like.

Antweight flippers are not generally effective at causing damage. They are popular in 'Sozbots' style arenas where a 'bot that leaves the platform looses. Flip 'em over the low arena wall and you win!

A: Lithium polymer battery packs require special chargers that generally run from an external DC power supply. If you want to get off cheap, you can use the battery from your car as that DC power supply. Alternately, you can run NiCad or NiMHd cells that are less picky about charging and buy an inexpensive AC/DC charger from EBay.

If you want cheaper still, run AAA alkaline cells and replace them every few matches.

A: A few years ago it was common to see antweight robots that used 'hacked' R/C servos as drive motors. Inexpensive R/C servos contain a small speed controller, a small DC motor, and a reduction gear train. They can be modified to provide rotating output rather than the stock back/forth motion (see: hacking a servo). Bolt on a wheel and you were in business!

Servo drives are nearly extinct now. They are slow and weak compared to other drivetrain options. You can build a robot with them, but you won't win many matches.

A: Flippers are powered by compressed gas. You'll need a cylinder to store the compressed gas, an actuator to move the flipper arm, an electric control valve to release gas into the actuator (and vent the pressure to lower the flipper), an interface to control the valve with your remote control, and hoses/fittings to connect everything up.

Getting all of this equipment small and light enough for an antweight isn't easy. Inertia Labs makes a full pneumatics kit for antweights, and they have a FAQ page that answers a lot of questions about antweight pneumatic systems. Give it a read!

A: Gee, everybody wants to build an antweight! I really like modifying R/C toys for antweights -- see the Toy Hacks and Kits section of the archive. If you want to build from scratch, visit www.sozbots.com and browse their FAQ and Tips page.

For a simple ant you'll need an R/C radio set-up, a two-channel motor controller (three if you want an active weapon), two motors with gearboxes, a small battery pack, a battery charger, and wheels. You'll need to make a chassis to bolt all that stuff onto -- aluminum, Lexan plastic, and carbon fiber panels are popular. Then you'll have to get enough armor together to keep it from being cut in two. This is getting expensive!

There's an antweight discussion forum at forums.delphiforums.com/antweights/start -- dig thru the information there for more tips.

A: The same armor materials used in larger 'bots works great on antweights. Titanium is the top-of-the-line, but is expensive, not easy to find, and can be difficult to work with. Polycarbonate plastic (Lexan) is inexpensive, widely available, and simple to cut and drill. I've used ultra-high molecular weight (UHMW) polyethylene plastic with good results on my beetleweight.

A: Combat robots are usually built to a maximum weight rather than size. Popular weight classes for small 'bots include:

• 1-pound (antweight);
• 3-pound (beetleweight); and
• 12-pound (hobbyweight).

A: Wow -- that's really light! In the U.S. we get a full pound for antweights - 454 grams.

I live near some places that build parts for airplanes and I can get scrap pieces of thin titanium that are great for robots. Titanium is light and very tough, but it's usually expensive and hard to find.

You might want to consider thin carbon composite material instead of metal. Robotcombat.com marketplace sells small sheets of it. It's very stiff and strong.

Some types of plastic make good armor for light robots, too. Polypropylene is used for kitchen storage containers and is very thin, light, and tough.