Society of Robots - Robot Forum

Electronics => Electronics => Topic started by: sohn on August 31, 2015, 04:33:32 PM

Title: Motor Question
Post by: sohn on August 31, 2015, 04:33:32 PM
I am looking at building a robot and I am trying to figure out what motor to use. I believe that the robot will weight no more than 100 lbs and it will have two drive motors (one on each side). Also I could use some help figuring out which controller I should use to control the motors.
Thanks in advance.
Title: Re: Motor Question
Post by: cyberjeff on September 01, 2015, 08:01:27 PM
There are a slew of wheel chair motors: (

Perhaps, put a bigger wheel on it, but not too big. A motor that is a bit oversize will run more efficiently. PM magnet motors like to be in the bottom half of the torque curve (which is more like a straight line running from no load to stall).
Title: Re: Motor Question
Post by: sohn on September 03, 2015, 01:34:28 PM
Thanks but what controller should I use with motors like those?
Title: Re: Motor Question
Post by: cyberjeff on September 07, 2015, 08:18:51 PM
Thanks but what controller should I use with motors like those?

You need a microcontroller such as an Arduino and a driver "shield" called a H Bridge. You need one strong enough that it handle the current.

Perhaps: (

I have no familiarity with controlling motors of that size so I am hesitant to give you advice on specifics.
Title: Re: Motor Question
Post by: ProgressiveAutomations on September 11, 2015, 02:09:59 PM
You can use old wheelchair motors like cyberjeff suggested.  I've used motors like that in making pumps and driving a ~300lbs bot, they draw from 20-50 amps.

One thing you have to be careful of with these big motors is the startup current.  You will most likely need to use a battery to power your system, because if you use a power supply, the start up current will trip the safety limits, and the power supply will shut down.

To pick an H bridge, you need to know the voltage of your motors, and the current draw. H bridges can usually take a variety of input voltages, from 5-40V, so the more important factor is the current.

There are two current specs that will be given for the H bridge, continuous and max.  The continuous is the one that you're going to spec-ing your limits with.  The max current limit is to account for the startup spikes that the motor will draw.  H bridges can usually only handle the spikes for <5 seconds.

For continuous current limits, I would pick an H bridge that is 150% more then the current of your motor. This depends on how often that you'll be using the motor, and how heavily loaded it is.  You could try and calculate duty cycles, and exactly how much current you'll be drawing at different times, but if the current draw is too close to the max of the H bridge for too long, it will burn out.  It's safer to overshoot, then your parts will last longer.

For controlling the H bridge, that depends on which one you get.  Some are controller with RC pulses, some take PWM inputs, and some have choices so that you can choose what you input.

We have a few control boards in our store, ranging from 10A to 120A. Here is a link, ( .If you're using wheel chair motors I would suggest a MegaMoto Plus (20A), MegaMoto GT (35) or a Vyper (120A). Some H bridges give you control of multiple motors, like our Scorpion (20A each channel).