Society of Robots - Robot Forum

Mechanics and Construction => Mechanics and Construction => Topic started by: omee66 on March 13, 2007, 07:02:17 AM

Title: Torque
Post by: omee66 on March 13, 2007, 07:02:17 AM
Hello everyone!
I've been a frequent visitor and have been reading the wonderful tutorials on this site-- they are very helpful.
I have recently started to work on my first robot, hopefully a line following robot. I constructed my motor drivers and it seems the small vibrating motors will not do. It is probably a torque issue, so I am wondering what is the best method to increase the power of my robot?
I was thinking this, but I am not sure how good it is:
http://elm-chan.org/works/ltc/ltc02.jpeg

Thank you!
Omar
Title: Re: Torque
Post by: JonHylands on March 13, 2007, 07:41:20 AM
Omar,

If you're building a pager motor-sized robot, you need to gear it way down.

Two easy ways to do this:

http://www.robotshop.ca/home/products/robot-parts/motors/gear-motors/low-cost-gears-motors/solarbotics-gm10-geared-pager-motor.html

http://www.robotshop.ca/home/products/robot-parts/motors/gear-motors/low-cost-gears-motors/solarbotics-gm15-gear-motor.html

Note that the second gearmotor is 4x faster than the first, so it will only work with small wheels - if you want to use larger wheels (say, larger than 1/2" diameter), go with the first option...

- Jon
Title: Re: Torque
Post by: omee66 on March 13, 2007, 08:05:55 AM
Thank you very much, Jon. I actually got these motors from those tiny R/C cars, so each has a very tiny gear and the wheels have a larger gear included. I suppose I can use those?

I was just a little confused, because that site I showed you used a tiny motor as well, without much gearing. Am I overlooking something?

Thank you very much!
Omar
Title: Re: Torque
Post by: Admin on March 16, 2007, 05:27:47 PM
because of volumetric scaling laws, motor torque decreases by the cube as size decreases linearly.

simply put, by laws of electromagnetics, tiny motors have almost no torque. :P

even worse, if you put gears (high precision gears required) on them, the weight of the gears plus efficiency losses kills what little torque they do have . . .

if you are trying to build a really small robot, you may want to consider using linear piezoelectric actuators (http://www.google.com/search?hl=en&rls=DGUS%2CDGUS%3A2006-11%2CDGUS%3Aen&q=piezoelectric+actuator) and piezoelectric motors (http://en.wikipedia.org/wiki/Piezoelectric_motor) instead.

this tutorial might also help you calculate what torque you require from your motors for your robot to work:
http://www.societyofrobots.com/mechanics_dynamics.shtml
Title: Re: Torque
Post by: omee66 on March 16, 2007, 07:03:36 PM
Thanks a lot :).
It seems that using a small motor might just be a drag. I'll stick to bigger motors, I suppose.

I guess my next question is-- how good are elastic bands for torquing?
I am thinking of making a large engraved slit in the middle of my wheels, and get rubber band to spin around them. This way, more torque and more power. I don't need to get up slopes or anything, just as long as my robot moves I'll be happy at this point :P.
So rubber bands, are they a no no?

By the way, Admin, you're like my biggest hero. So the fact that you replied, I feel special :P.

Thanks,
Omar
Title: Re: Torque
Post by: Admin on March 17, 2007, 04:51:05 PM
Quote
I guess my next question is-- how good are elastic bands for torquing?
I am thinking of making a large engraved slit in the middle of my wheels, and get rubber band to spin around them. This way, more torque and more power. I don't need to get up slopes or anything, just as long as my robot moves I'll be happy at this point .
So rubber bands, are they a no no?

took me a bit to figure out what you meant . . . good thick rubber bands might work but since they are elastic they are hence a bit unpredictable. have you considered the mouse trap car idea (http://images.google.com/images?sourceid=navclient&ie=UTF-8&rls=DGUS,DGUS:2006-11,DGUS:en&q=mousetrap%20car&oe=UTF-8&um=1&sa=N&tab=wi)? i made one many years ago and it was really reliable - just make sure you do the gearing calculations/guessing properly (wheel diameter vs spool diameter ratio). :P
Title: Re: Torque
Post by: omee66 on March 17, 2007, 09:14:13 PM
Actually, I am making a line following robot using a 16F684 microcontroller (due to its A/D conversation for the sensor)-- so I am using motors and wheels. That is why this dilemma started.

Any tips?