Robot haiku:

Effective spinners Take work and careful planning. Some work - most do not.

A: There are several different Black & Decker power screwdrivers, but they all have the same output shaft design: a tube about 3/8" in diameter with an internal 1/4" hex drive. Those dimensions are WAY too large for the Lite Flite wheels (max drill out 3/16"), and I certainly can't recommend glueing the tire directly to the gearbox output shaft! You'd have no lateral support, and no way to quickly replace a shredded tire.

The best wheel solution might be to run the BaneBots 3/8" hub with BaneBots 3/4" hex mount wheels. Measure your output shaft diameter carefully -- you may need to reduce the diameter a bit. The hubs are heavy, a little expensive, and overkill -- but that large gearbox shaft is really awkward. I hear that you're on a tight budget, but a hub solution is NOT the place to economize! I think I've seen more robots fail from poor/hacked hubs than any other single cause.

I should also point out that the 'bot is going to be slow. Power screwdrivers are more about torque than speed, and unless you're running serious overvoltage and really big wheels, you're gonna be at slow walking speed. I think you might be money ahead to switch to more conventional gearmotors to gain speed and the ability to use standard hubs and wheels.

Robot haiku:

Power screwdrivers? You're starting to figure out Why they are not used.

A: I don't know of an 'HHX' desination for timing belts, but I do know about 'XXH'. There are six standard 'pitches' of synchronous timing belts for different levels of power transmission:

For more information about timing belts than you'll ever need, take a look at GatesFacts: Differences in Synchronous Belts.

Robot haiku:

Match the pitch and width Of belt to motor power Or you'll watch it fail.

Q: Dear aaron, I know that team whyachi has a robot called warrior SKF.Do you have any information about it? How its toothed spining ring powered the flipping arm? & can you please give me its tech specification about its drive, weapon &its design . [Mumbai, India] A: We have discussed 'Warrior SKF' several times previously. Search the archive for multiple posts. Robot haiku: Please search the archives Before you ask a question. It saves us both time.

A: You might benefit from reading this post on RCGroups.com. If that doesn't help, your closest support center is Horizon Hobby Limited in the UK:

Robot haiku:

Transmitter made for Blade SR Helicopter. Not good for much else.

Thanks for your time
Neil

A: First, I need to talk you out of your ESC setup. It's generally a really awful idea to attempt to control a motor with two ESCs -- particularly if those two ESCs are providing different power levels and polarities! An ESC controls power by switching it on and off very rapidly. The relative time spent 'on' determines the power supplied to the motor(s). With your setup, if you are moving forward and attempt to turn, the motors on opposite sides of the robot will get conflicting power pulses from the ESCs:

• The motors on the 'outside' of the turn will receive one set of power pulses from the drive ESC at one power level, and a second set of pulses at a different level from the turn ESC. Sometimes these pulses will overlap, sometimes they will be independent. The result will be unpredictable motor speed.

• Far worse, the motors on the 'inside' of the turn will also be receiving overlapping/independent power pulses -- but with opposing polarity! This is a wonderful way to melt both of the ESCs. You're essentially creating a direct short circuit.

Your questions about robot gyros are answered in the Team Run Amok Beginners Guide to Combat Robot Gyros. I'd suggest you test the robot without a gyro and consider adding one only if you have trouble maintaining a consistent turn rate or have issues with the robot 'spinning out'. Note the warnings in the gyro guide concerning invertible robots.

Robot haiku:

Multiple motors From one ESC is fine. Not the other way!

Thanks for your help.

A: Your concerns are well founded. Bevel gears are inefficient at power transfer, and are sensitive to shock and misalignment. Off-the-shelf gearboxes are expensive, limited in speed and power inputs, and difficult to interface.

Your current belt drive is very efficient, tolerates shock loading, and can handle misalignment -- a great deal of misalignment. Consider a quarter-turn belt drive. You may run into some problems that will require some tweaks to the design, but I'd rather try a quarter-turn belt drive than a bevel gear system.

I can't directly comment on whether going to a horizontal weapon motor is worth the effort. If your weapon was working well, perhaps you shouldn't tamper with the design. Keep it simple.

Robot haiku:

Don't complicate things. Change things that break or don't work. If it works, keep it.

A: I think it's way too late. The UK touring events - like Robots Live - were able to get on their feet while the interest from Robot Wars was still very strong. The robots and teams were well-known to a large potential audience, and the transition from popular television show to live event went quickly and smoothly.

It's also a simpler task to drag an arena and robot teams around a relatively small area like the UK than it would be to do the same with major venues in the US. I don't see a touring event working in the current US combat robot environment.

Robot haiku:

The UK maintained Momentum from Robot Wars. Too late for US.

A: I don't know of any Team Velocity robot named simply 'Velocity'. You may browse thru the team's robots at the Team Velocity Website for information on their 'bots.

Robot haiku:

They have a 'bot named 'Terminal Velocity'. Middleweight spinner.

Q: Dear Aaron, I know that Team Velocity has a robot called Trilocity. Do you have any information about it? Are there any videos? [China]

A:This time you got it right! We know 'Trilocity' -- we fought it at one of the DaVinci Days events (we won!). 'Trilocity' is a beetleweight thwackbot with an overall record of 9 wins / 5 losses. It's very difficult to get a twackbot to work in a small insect arena, but 'Trilocity' was quite successful due to a well thought-out design and a great deal of drive power. I don't know of any available videos. Robot haiku: Spinning a thwackbot In a tiny arena? Very hard to do!

A: Mark J. here: a typical starter motor is of an essentially different design than the AmpFlow motors.

• The AmpFlow motors are (like other commonly used robotics motors) a permanent magnet direct current (PMDC) design. Such motors have a linear torque curve, produce maximum horsepower in the middle of their speed range, have a stable output speed, and are simple to reverse. This type of motor is broadly used in robotic applications.

• A typical automotive starter motor is a series wound stator design. This design is good at providing high torque for short periods of time, but their torque falls off rapidly with increasing speed. Their speed stability is poor, and reversing their rotation direction requires additional switching controls. They are generally unsuited to robotics applications and are very seldom used.

Many small robots use brushless 'outrunner' motors for their spinner weapons, but an outrunner motor powerful enough to spin a weapon for a large robot would be expensive, difficult to find, and untested. All brushless motors require a special brushless motor controller to provide correctly timed and directed current pulses to the field windings of the motor. A diagram depicting the electrical layout of the brushless controller/motor can be found here.

Robot haiku:

For component choice, Use proven and tested parts. There are good reasons.

A: Mark J. here: the diameter of the weapon disk is critical in the computations. If the disk is aluminum, I can estimate the diameter of the disk at 50 cm to get a 1 cm thick disk up to 6 kg. I'll also assume this is for a 60 kg 'bot.

An effective spinner weapon should have at least 16 joules of energy per pound of the weight class -- in your case that's a little over 2000 joules. You also need to be able to spin the weapon up to speed before your opponent can sprint across the arena and ram your weapon to slow it and keep it from reaching dangerous energy levels.

The Team Run Amok Spinner Spreadsheet says that the HF drillmotor/gearbox can spin your weapon disk up to about 800 joules in six seconds. That's too long a spin-up time for a small arena and too little weapon energy for a 60 kilo robot. You'll need both more power and speed.

Aim to spin the weapon disk to about 1500 RPM, reaching 1000 RPM in the first 2 seconds. You'll need about 1.5 horsepower to do that, and the 18 volt HF drill motor is good for only about 0.5 horsepower.

Robot haiku:

Question, India: If you lack heavy motors, Why build heavy 'bots?

Q: hey Aaron its that 900 rpm HF guy again, actually its for a 25 kg bot .....the disk will be 12 cm in diameter and made of cast iron ......maybe 6 kg will be too heavy , so m planning to use 4 kg , 1 cm thickness .....what now ? .....can u suggest any better material ?

A: Your calculations are off someplace. A 12 cm diameter cast iron disk 1 cm thick has a mass of only 0.9 kilo. That's WAY too small to be an effective weapon. Note that our spinner spreadsheet asks for the radius of the disk in its calculations, not the diameter. A 12 cm radius cast iron disk 1 cm thick has a mass of 3.5 kilos -- let's go from there:

As to your material choice, cast iron is brittle -- it tends to shatter when hit hard. Most spinner discs are made from aluminum alloy with tough steel impact blades bolted on. All steel construction could work for your weapon.

Robot haiku:

Spinner must be tough. If it shatters on impact You will loose your match.

A: Mark J. here: those are very weak motors for a 20 kilo robot. Even with six of them, you'll need small wheels (about 2.5" diameter) to generate maximum pushing power without stalling the motors, and the top speed will be only 2 MPH. Sitting duck! Consult our Optimum Gearing for Combat Robots guide for information on speed, torque, and gearing.

The ability of one robot to 'push' another robot depends on many factors. Interestingly, the torque and speed of the drive motors are NOT directly among those factors. Correctly geared, more powerful motors won't give you more direct pushing power, but you'd gain much greater speed and ramming ability.

I don't have the space or time to run thru the full course in kinetics principles, but here are the high points:

• The maximum pushing force available to a robot (assuming correct motor gearing and wheel size) is dependent on the weight supported by the driven wheels and the coefficient of friction between the tire material and the arena surface.

• Pushing force is used to accelerate the robot. More force will accelerate the 'bot quickly, less force will do the same job more slowly. Net pushing force will be diminished by external forces acting on the robot, and 'pushing another robot' qualifies as an external force. The degree by which your available pushing force is diminished varies with the actions of that other robot. Pushing force in excess of the combined forces acting to impede your robot may be used to accelerate the combined mass of the two-robot system (push your opponent).

• In theory you will not be able to directly 'push' a heavier robot that has a coefficient of friction equal to your own and its wheels locked (or pushing back). You may, however, be able to reduce the resisting force of the other robot by lifting some of its weight off of its wheels by use of your wedge. This may also increase your own pushing force by placing a portion of your opponent's weight onto your driven wheels.

• You may also move your opponent by 'ramming' -- transfering the kinetic energy stored in your moving robot to your opponent. This effect is additive to the direct pushing force of your robot's drivetrain.

Robot haiku:

Push them or be pushed. It all depends on traction, Not motor power.

A: A pair of the 'new style' DeWalt 18 volt motors running at 24 volts would typically be used in a robot no heavier than 120 pounds, but will give fair performance for an 80 kilo 'bot in a small arena. I suggest locking the transmission in 'low' and fitting wheels about 4" in diameter. Peak current consumption will be close to 50 amps per motor at full push.

Many builders prefer the 'old style' 18 volt DeWalt motor and 2-speed transmission, viewing it as stronger and easier to adapt to robot applications. With either motor you will need to develop your own output shaft and bearing support solution. Team Delta offers 'old style' DeWalt motor mounts, bearing blocks, and output shafts that you may find useful -- but I'm not certain that they are still in stock.

There aren't many proven motor options available for your weight class and budget. If you're willing to consider 4-wheel drive, four of the inexpensive Harbor Freight 900 RPM 18v Drills may be disassembed to provide motors and gearboxes suitable for robot applications. Many budget robots have been powered by these motors with good result -- a web search for "harbor freight drill hack robot" will take you to info on using these motors in a combat robot. Four would give power comparable to two DeWalts.

Robot haiku:

OK power if 'Bot has an active weapon. Rammer? More power.

Q: After reading the product manual for the 18 volt Harbor Freight cordless drill the max torque shown in specs is 7ft-lb... and 84ft lbs on the link you provided. Can you please sort it out?

A: One of the things you pay for when buying premium components is correct specifications. Cheap gear typically has either no specs or unreliable specs. The 84 ft-lb torque number on the webpage is a typo that should read 84 in-lbs, which correctly converts to the 7 ft-lbs figure given in the manual.

Robot haiku:

Premium products Take time to give you good specs. Cheap stuff, not so much.

A: Kind of a broad question. We've discussed the design of 4-bar mechanisms many times previously -- you can find those discussions in the archive. Search there for '4-bar'.

If you have specific questions on topics not previously covered, write back.

Robot haiku:

Specific questions Will get specific answers. Please check the archives.

A: If the wheels are protected, I like BaneBots. If the wheels are unprotected, the tougher LiteFlites are a better choice.

DO NOT try to get away with press-fitting wheels onto motor shafts! Dave's Hubs are very strong, compact, and make it simple to replace the tires when they get chewed up. I think they're well worth their price, but there are other options. The Astroflight prop adapter makes a good hub solution if you're willing to drill out the Lite Flite wheel a bit, and the FingerTech hubs are functional and very light. Whichever you choose, check the tightness of the hub set screws before every match.

Also, consider a larger diameter wheel with the B16 motors in an antweight. A 2 1/2" wheel would give great performance in an 8 foot arena.

Robot haiku:

Lite Flites absorb hits That would destroy the BaneBots. I'd buy the good hubs.

A: See #17. Performance of a robot component depends on both the material and the design -- I can't recommend a specific material.

Mark J. here: Aaron is correct, but on a practical note your choice of aluminum may come down to what you can find. The 6061 alloy is widely available in a variety of shapes and forms, while the stronger 'aircraft grade' 2024 and 7075 alloys are harder to find -- as well as being more difficult to work with. Don't design for material that isn't available.

Robot haiku:

Too little info. Material and design Must work together.

So what will you suggest AmpFlow or NPC ?

A: Mark J. here: I don't think the RioBotz tutorial got this bit quite right. In real-life conditions, the NPC-02446 is in no way comparable in power to the AmpFlow F30-150 -- or even the E30-150.

Here's the deal: in actual robotic application, the additional resistance of the battery and speed controller can be important when calculating the maximum (stall) torque of high-output motors. The lower the armature resistance of the motor, the larger the effect will be. However, a permanent magnet DC motor generates maximum horsepower at 50% of maximum RPM -- at a point where the counter-electromotive force generated by the rotating armature adds a considerable effective resistance. The impact of battery/controller resistance on horsepower is much smaller than the values cited by RioBotz.

Second consideration: I suspect that those NPC numbers from the dynomometer use a really huge low-resistance battery and no controller at all. You must be VERY careful when comparing motor power measured under apparently different conditions.

A simple method to compare the approximate output power of two brushed motors is to use the following formula on each motor:

The formula makes many assumptions, including equal efficiency of the motors, but it gives an estimate of the power output that is independent of variables such as battery and controller resistance. Using this formula, the numbers come out as follows:

• NPC-02446: 488 watts = ~0.65 HP
• AmpFlow E30-150: 750 watts = ~1.0 HP

Robot haiku:

Be sure to compare Numbers that mean the same thing: Apples to apples.

A: The FingerTech kit is largely a collection of components and raw materials that requires a good amount of fabrication and finishing to turn into a combat robot. It is suitable for a builder with good basic shop skills and a collection of suitable shop tools.

The quality of the finished robot is likely to vary greatly with the skill level of the builder. I would not recommend the kit for a novice builder. Review the kit instructions and make a realistic decision as to whether your building skills are up to the task.

Mark J. here: one comment on the construction techniques used by the kit. The design calls for mounting holes to be drilled very close to the edge of Lexan armor, placing high localized stress on the Lexan and possibly causing cracking and break-thru in those areas. I would suggest cutting the Lexan wider and/or changing the mounting points to move those high-stress areas further away from the armor edge.

Robot haiku:

If you've got the skills, Maybe you don't need their kit. Make one for yourself.

A: A very ambitious project! Several comments: Splitting your weapon weight allowance between two weapons is a poor idea: see #26. You can only use one of the weapons at a time, and each is half the weight and power it might be if it were the sole weapon. Air tanks come in a variety of types and sizes. 'Ziggy' uses a standard SCUBA tank -- check diving supply sources. Many large robots use CO2 fire extinguisher tanks that are available in a range of sizes. Make certain the tank you choose is rated for the pressure you plan to use. The 'What a gas!' section of the Team Da Vinci: Understanding Pneumatics page has a good discussion of the properties and advantages of different gas types for pneumatic weapons. There are too many suitable motors for a 60 kg robot for me to provide a list. We have discussed using the Team Tentacle Torque/Amp Calculator to evaluate motor performance many times -- see the archive. A pair of PDX26 motors would not provide good speed or acceleration for a 60 kg robot in a small arena. Four PDX26's in a 4-wheel drive configuration would be adequate if used with small diameter wheels (~2.5"). I would strongly suggest that you support the outside ends of the PDX26 output shafts with bearings for a 'bot this heavy. If you look at the motor performance specifications you'll quickly see why AmpFlow motors are used by many successful Indian robots. Robot haiku: General advice: Keep your 'bot design simple, And build for great strength.

Undesireable!

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