# Arduino armwrestling video-contest!

The idea of this contest just striked me: Use a given lenght of "arm" and a maximum of e.g. 3 motors ( servos, stepper, fans, watercoolingpump, whatever ) and compete against a scale or another competitor. Show us a ( uncut ) Video of your results.

Should we start with a beginners class with the cheap and welknown 28BYJ48 Motor with ULN2003 Controller?

May the torque be with you :D

Any limits on power supply? Geared motors? Electric only? etc. Otherwise one could bring in gas engine with arduino controlling the throttle, lots of horsepower to pull any arm down.

Armwrestle it your self first :) Man against robot.

Max motorpower for all contestants will make a tie.

Sure, I meant electric motors/actuators. When it is about torque, I would always choose an electric Motor.

To limit the powersource would make insane constructions impossible and more comparable. We could define different power classes. We could also set a time limit, so no one could build a mega ratio gearbox .

My Intention is to see different sketches and different arm-constructions battle against each other in a achievable and funny way. ( not like Robot wars )

The thing is that the same Power will make the same tourqe regarless of Construction.

If both you and I use a motor with 300w and I use a gearbox 3000:1 and you use a gearbox 30:1 it will still be a tie.

Your arm will slam into mine but it will still be 300w from both arms and a tie.

Why not set a build cost classes.

You could have an under \$50 and under \$100.

janost: The thing is that the same Power will make the same tourqe regarless of Construction.

If both you and I use a motor with 300w and I use a gearbox 3000:1 and you use a gearbox 30:1 it will still be a tie.

Your arm will slam into mine but it will still be 300w from both arms and a tie.

Hmm, I've learned two equations regarding power:

P = U* I or P = torque * RPM In other words:

Torque = Power / rpm

To me it sounds like the slower Motor ( gear Ratio ) has more torque, right?

Today I added a few Drops of " ferrofluid" in the airgap of a 28BYJ. I expect to increase torque, but for now I can't tell any numbers. With a little change in the sketch, I could get 25rpm with a 3s lipo. It was 19 rpm before I added the magic fluid.

BTW: there is plenty of room left to rewind the coils with thicker wire. Now that I improved the "airgap-limitation" it would make sense...

If I recall from months ago I had 35 RPM with 12v. I'd like someone to verify your results! Sounds amazing!

For now I only have a ferrofluid with µr = 1.96.
That’s roughly twice as good as “air”. But I could get a fluid with µr~20, but the sideeffect is, that the fluid gets thicker too.
The cool thing abot the fluid and the 28BYJ is: you just have to remove the sticker on the back and put a few drops of fluid in the gaps.
Rewinding the coils is a bit tricky. You have to disassemble the gears and it’s pretty hard to reassemble them later.
It would only make sense, if we had a better driver than the ULN2003. ( 4 power FETs would do? )

Just found a Video, how to make your own ferrofluid: