Motor strength (chosing motors)

[mgolu24]

Please help me whit motors. I dont know what motor to pick for driving my robot. i want to make a fighting bot so moving around 10-20kg. please help.(btw the robot will slam others, it wont use any weapons so it hast to move fast)

thanks

[Admin]

This tutorial tells you how to calculate it:
http://www.societyofrobots.com/mechanics_dynamics.shtml

If you have trouble, just tell us what is confusing and we will explain.

For ramming style battlebots you want the highest momentum possible, so choose a high velocity and acceleration.

[mgolu24]

i dont understend many things on the page. maybe it would be so hard if i would know more english. i know english but i dont understeand velocity, torque and things like that.the bot will (must) be under 1000mm x 1000mm x 1000mm (1m x 1m x 1m) dimenzions. i intend to figth bots like these http://borberobota.com/roboti/roboti.htm , so i want a motor that moves my robot so that i can crash into the other robot whit my spikes , oh and it would need maybe a litle bigger wheels because i intend to have the wheels on the both side, cause if the bot flips so i can continue fighting

[Admin]

haha ok, that explains the strange typos . . .

Velocity is how fast the robot moves. If you are driving a car at 30km/hr, that is velocity.

Acceleration is how fast the robot can increase velocity.

I recommend using about 1.5m/s acceleration, with velocity at 2m/s. Lets say mass was 20kg.

Now use this equation:
Torque * rps > = Mass * Acceleration * Velocity / (2 * pi)
this becomes
Torque * rps > = 20kg * 1.5m/s * 2 m/s / (2 * pi)

Now find a motor you like to buy, and multiply the torque and rps of that motor together. If that number is higher than the calculation on the right side of the equation, then that motor will do what you need.

If you cant find a motor that will work, you will have to reduce expected mass/velocity/acceleration.

[mgolu24]

yea i type bad 

hmm how do i get torque? i know torque is distance * force, but where can i get these information?

[Admin]

Just look at any motor specifications sheet. All motor spec sheets (at least the useful ones) include this information:

• voltage
• no load current
• stall current
• stall torque
• rpm or rps

[mgolu24]

so by my calculation two "AME 12v 88 in-lb gearmotor w/pinion (210-1009 - 210-1012)" motors (for diferencial drive) on this site http://www.robotmarketplace.com/marketplace_motors_ame.html ( the second motor) should be enough.

what about wheels?

[Admin]

Check the equation on that very same tutorial 

http://www.societyofrobots.com/mechanics_dynamics.shtml#wheel

[mgolu24]

oh yea... thanks for all that info

[mgolu24]

so i was looking around for some cheap motors today, and i found this http://www.robotmarketplace.com/marketplace_motorsmisc.html the "ML-50 50:1 Gearhead Motor" . i think it should be good for my statisfaction. i was thinking to buy four of them and place one on each wheel, should that be enough? (i know i have the formula but the units just confuze me ).

oh and is it better to have four 12v regular electric (it think they are called dc motors) motors whit gearboxes or four "ML-50 50:1 Gearhead Motors"

[Admin]

i didnt do the math, but i dont think they are powerful enough.

I have that motor actually and for a 20kg battle bot I seriously doubt it will be enough. You probably want something twice as powerful . . .

But again, do the math . . .

If you are confused with units, go to google and type things like 'convert 20kg to pounds' and it will do it for you.

[mgolu24]

so by my calculation these two motors http://www.lynxmotion.com/Product.aspx?productID=183&CategoryID=72 should be more than enough, actually one would be enough

[Admin]

14000 rpm! hmmmm noooo you want something geared down. this motor is really fast, but also really weak. weaker than the other above actually too.

[mgolu24]

so why is it so that you need to gear those high rpm motors down? i dont get it

[Admin]

Because it has very very low torque if you dont.

[mgolu24]

oh... i think i have found the best solution. Accumulator boring machine! i will install four of these things on my robot. I think it should be enough (for a 10kg robot or even less). And whit the accumulator boring machine i get 4 batteries and 4 chargers!!! i think ids a great idea