Which motors should we use?

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Posted by CArobot at 1/16/2001 6:14 PM EST


Other on team #619, CArobot, from Charlottesville Albemarle.



We are going to build a robot that very closely approaches the weight limit and carries the tower. This means carrying 200 pounds across the floor on two wheelchair wheels and two trailing casters. Is it best to use the drill motors or the fisher price motors? four inch wheels or six inch wheels?

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Posted by Rob DeCotiis at 1/16/2001 6:21 PM EST


Student on team #504, RoBUCtics, from Red Bank Regional High School and Jesel.


In Reply to: Which motors should we use?
Posted by CArobot on 1/16/2001 6:14 PM EST:



i'd suggest that you use the drill motors, 6 " wheels, but why not just experiment with them? you could just use the drill motors, and if they end up not working out, just modify the robot and use the fisher price ones...

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Posted by Jake at 1/16/2001 7:43 PM EST


Student on team #365, Miracle Workerz, from Avon Grove High School and DuPont Engineering.


In Reply to: Which motors should we use?
Posted by CArobot on 1/16/2001 6:14 PM EST:



The Drill motors have more RPMs and more Torque than the fisher price motors. M.O.E. (Our robot last year) used a dual drill motor drive and two casters. We were able to push with the big boys, when the time came.

As for the 6" vs 4" wheel, there is a trade-off. You could use the 6" wheel with a basic chain-drive system, so you could move around with some speed, and have a respectable amount of torque. I believe we used a 3:1 ratio of drive gear teeth to wheel gear teeth (might be wrong.. the ratios were never my strong point). If you want to go with the simpler direct drive aprotch (Putting the motor right into the wheel), I'd use the 4" wheel. It will give you more torque, where as the 6" wheel would make you go faster with less torque.

I would probably recomend the Drill motor with a chain drive to the 6" wheel. If you'd like some documentation on motor specs and gear ratios, visit our web site and get in touch with one of our engineers. They'd be happy to send you a packet of information on any range of topics.

Best of luck to you!

~ Jake

: We are going to build a robot that very closely approaches the weight limit and carries the tower. This means carrying 200 pounds across the floor on two wheelchair wheels and two trailing casters. Is it best to use the drill motors or the fisher price motors? four inch wheels or six inch wheels?

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Posted by Joe Johnson at 1/16/2001 9:17 PM EST


Engineer on team #47, Chief Delphi, from Pontiac Central High School and Delphi Automotive Systems.


In Reply to: Which motors should we use?
Posted by CArobot on 1/16/2001 6:14 PM EST:



It is my belief that at a minumum, a drive system
should be able to break the wheels free rather than
stall the motors.

This does not pick your motor, but it does pick the
lowest gear ratio you can used with any particular
motor (which really means it determines your top speed).

I would calculate what weight you expect to be put on
your drive wheels, multiply that by .5 or so as an
estimate of the coeficient of friction and then
multiply that by the radius of the wheels. This will
give you a toque needed to break the wheels free.

Divide this torque by the stall torque for the motor
multiplied by an estimate of the efficiency of the
drive train (for example .9 per spur gear stage, .9 per
chain stage, .3 for a work drive or a jack screw, etc.)

This number is the ratio your drive train will need.

Now calculate the free speed of you wheels. Is that
fast enough? If not you need a more powerful motor.

The most powerful motors in the kit are the drills (by
far) followed by the Fisher Price motors, the Globes,
the Power Sliding Door motors, etc.

See several of the white papers on motors on this web
site for more information on motors and power calculations.

Good Luck,

Joe J.

The