Need Advice Choosing Servos for Astromech Propulsion (2WD)

[mattkw80]

Hey Guys,

New to Robotshop - love the site, love the store.

I am building a "mini" Astromech (R2D2 clone). I say mini,?
because instead of a full 18" and 200 lbs, mine is going to
end up being approximately 10" and 10lbs. (Made of plastic).

I have googled for hours, and cannot find any clear advice on
what servo motor's I should look at for the wheels under the feet,
which are attached to the legs.

I plan on getting castors working first, so that basically the robot
will be on roller skates - and then add the motorized wheels on to that.

Can anyone point me in the right direction in terms of a set of motors or
maybe a base kit I can buy, and then rig up into the feet? I'd be willing
to spend upwards up $100 per foot. I would be willing to cut up an existing
2WD kit if necessary - or just buy the specific motors individually.

Is Servo motor's the way to go with this, or should I be looking at DC Motors
with a motor controller?

For what it's worth - I am using an Aruduino as a brain.

[Cbenson]

If the robot will weigh around 10 pounds, you should not be considering continuous rotation servos; DC gear motors are the way to go. You can get an idea of what motor you'll need based on the Drive Motor Sizing Tool. You will likely be considering either planetary or spur gear motors. We have this article to help you choose a motor controller.

[mattkw80]

Thank you for the reply - dumb question - will I be able to control the speed?
I'm somewhat concerned that going to a DC motor and motor controller will result
in turning my robot into a faster then expected remote control car.

[Cbenson]

There are two ways to control the speed of a DC gear motor:
1) Choose the correct gear ratio: the higher the gear ratio, the lower the final speed.
2) Use a motor controller: motor controllers allow you to vary the speed from full stop to full speed in either direction.

[mattkw80]

Small change in plans... having changed the dome from Stainless Steel to plastic, looks like I can get the weight down to around 4lbs. (Instead of 10lbs). At 4lbs. do you still suggest a DC Motor Controller and DC Motors or do you think I could get by with some continuous rotation servos?

I used to own a Boe Bot, and although I know those are considerably lighter, the wheels on those are driven with x2 continuous rotation servos.

[Cbenson]

At 4lbs, you're at the limit of what a normal continuous rotation servo can support, so we would still suggest a DC gear motor at this time. The fact that the weight will be distributed over more than just the two drive wheels helps a bit.

[mattkw80]

Thanks for all of your advice.

I ordered this: http://www.robotshop.com/ca/drive-system-12-volt.html