Let's Make Robots!

hobby motor control

Hi guys, I am looking into getting a small electronic speed controller from the rc hobby store to run a couple of small dc motors (tamiya dual gearbox), does anybody know if these take the same pwm input as running a servo or does the r/c gear use something else? I thought r/c gear used pwm but when browsing online for motor controllers some say pwm, and some say r/c (in addition to analog or serial or whatever else). Is there a difference? Also, some use a battery elimination circuit, which means the reciever unit (which is sending the signal to the esc) will draw power out of the esc through the same cable, "eliminating" the need for two batteries. this sounds like bad juju for the electronics I am planning on controlling it with (basic stamp... shut-up ;). does anybody know more about these hobby controllers?


- Frank

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..I decided to see if anybody got back to me,  perfect timing robologist!  This is all coming together, .  What I think I'll do is just wait until they start to go, and by then Im sure ill need something else so ill get those 6v RM3s.  I still have one extra fa-130 from the single gearbox which came with the treads to hold me over if one of them goes.  I think I'll stay away from the serial controller for now too, because I havent done any serial programming yet, though Im sure I will have to figure it out sooner rather than later.

thanks Jim! I guess i could have figured out that the rc cars use pwm if you can just unplug the esc and use a servo.

so it would have worked but.. I just got this kit from solarbotics;

Solarbotics L298 2A 6V-50V Compact Dual Motor Driver Kit Solarbotics L298 2A 6V-50V Compact Dual Motor Driver Kit

this will give me some much needed soldering practice too! this way since i plan on using a microcontroller, I will know exactly what the motor controller is doing, unlike the esc which can do some random stuff you were saying. however, if i were to hook up an r/c reciever or use pwm would the L298 understand it? i dont think it will. If I make a simple H bridge can you feed that pwm? mabe i should try it..

One more question though.. can I use any type of battery? i had a 7.3v 650 mAh that i was planning on using. Im just not sure if it will fry my tiny motors (fa-130), even if it goes through the controller. do I need to use a 3v source?

motor specifications:

  • Operating voltage: 1.5-3 V
  • No-load speed at 3 V: about 12,300 RPM
  • Stall current at 3 V: about 2.10 A
  • Stall torque at 3 V: about 36 g-cm

thanks for your help!


Those little Mabuchi FA-130s used in the Tamiya gearbox can be difficult to work with. The L298 motor controller you have is nice, but requires a minimum of 6 volts on the motor supply. The FA-130 motors operate ok at 3 volts, and will fry at a higher voltage. I've experienced this from using them on a minisumo, which had 6 volts to a pair of A3952 drivers with similar charecteristics to the L298. The motors were only seeing around 4 volts, and would have to be replaced after so many rounds. Pololu did some testing of  these motors at higher than spec voltages shown here : http://www.pololu.com/docs/0J11 The sort of good news, is that the L298 motor driver will lose about 2 to 2.4 volts across the transistor junctions, so whatever supply voltage you have, the motors will 2 volts less or so, but that did not help in my case.

There is a Solarbotics RM3 motor that fits as a good replacement here : http://www.pololu.com/catalog/product/604 that operates at 6 volts just fine, and draws a lot less current.

As yet another alternative, Pololu offers a Low Voltage Dual Serial Motor Controller that can deliver the low voltage needed by the FA-130 motor, shown here: http://www.pololu.com/catalog/product/120

Hi Frank,

I have been using an ESC myself for controlling my R/C robot car Robot Hansen. The ESC takes a standard R/C servo signal as input (since you can just replace an ESC with a servo mechanically pulling an arm between contacts which was the way Tamiya cars used to do the speed control in some of their cars) and uses this to control n H-bridge using PWM for speed control.

Robot Hansen's control circuit gets its power directly from the ESC and this works nicely. I would think that the LM-406FB has a 5V 7805 voltage regulator that can supply 800 mA and that should be enough for most control circuits.

I think your idea of getting an ESC to run both motors in the Tamiya dual gearbox would definitely work but it's a rather expensive setu, since you'd need an ESC for each motor and ESC's are quite expensive in comparison to the cost of building your own motor control circuit. You should also be aware that some ESC's (like the one I have) interpret the input signal like for example when I change quickly from forward to reverse on the radio controller the ESC will activate the electronic brake. Also my ESC won't drive in reverse as fast as in forward.

If money's not the issue I would recommend you getting a real dual motor controller (or build one yourself if that's an option).

- Jimmy