Dual Serial Mot. Controller: Motor stalls or won't run


I recently purchased two Dual Serial Motor Controllers for a small project.

I am using a PC for control and assembled the RS232 -> TTL adaptor as stated in the manual. This works good together with the serial servo controller which is connected to the same line as the motor controller.

My problem is now, that my motors won’t run at all or stall soon after they start running (one motor is equal to Radio shack #273-258 with 1.5-3VDC, an other is probably for 5 or 6 volts).

I am still new to electronics and don’t know if this is a simple problem related to current/voltage or a problem with the controller. I am using a 8VDC/0.4A max. power source and use the big capacitor (the small one provides the same result).

I have modified the Cygwin/TCL source code provided by pololu and added a simple scroller for each of the possible two DC motors which seems to work in principle.

Any help will be greatly appreciated!!!


The 400 mA max. on the power supply is probably your problem. A low-voltage motor will typically draw a lot of current. I don’t know what you’re using for your power supply, but it sounds like it might be one of those unregulated “wall wart” type power adapters. If you’re getting the 8V rating from a no-load measurement, the voltage might be quite different under load. In general, those power supplies are not very good for motors.

- Jan

Hi Jan,
this is the adapter of an old mobile phone - but now I also tried an other one with 1 amp at 7 VDC - but the same result.

What would you suggest to use?

Can I damage my PC/serial port in using a “bigger” adapter - because they are connected to the same ground? Do I have to use a resistor then?

thanks for your help!

How are you verifying your power supply specs? Have you figured out how much current you need? In general, we recommend using batteries such as NiMH rechargeables. If you can’t use batteries, a bench top supply that gives you voltage and current control would be good. There are many of these available for $100 or less from various electronics supply stores.

It’s always possible to damage your PC with anything. It’s certainly possible that you could make things work, too. If you’re concerned and not too sure of what you’re doing, a good way to get a bit of extra safety might be to get an external USB hub and a USB-to-serial adapter. You’d really have to do something bad to do more than damage the hub.

- Jan