PWM on baby board

I’m Richard from Romania.
I’ve recently bought a Baby Orangutan robot controller mega48 (the old one) and a Tamiya 70168 Double Gearbox Kit. The gearbox kit has 3V motors, but my accus are at 6V. I want to go with 6V, so I was thinking of having PWM at 50% (after transistor loss, of course) in max. Or maybe a bit higher, just in case it will ever be needed.
I’ve seen experiments conducted here (nexisnet), where motors at 6V ceased to operate in five hours and half (running continuously). I believe that integrating a 6V PWM at 50% at most won’t have the same effect, but I wish some opinions.

As another point, what is the max operating frequency of the chip ? (LB1836M). Nothing is specified in the datasheet (or I haven’t found it). I’d like to go beyond audible range.

Hi Richard,

I agree with you that limiting the PWM duty cycle to 50% will probably make your motors last a bit longer, but not as long as actually running them at 3V (sorry I don’t have any motors left to test this). If you’re not happy with the 50% speed limit though, I wouldn’t be afraid to just run the motors at 6V. If you’re doing speed control you won’t be running them that hard all the time, and even 15 hours of operation is pretty long for a hobby robot. Also, Pololu now stocks spare FA-130 motors, but I imagine shipping to Romania would add a lot to the cost.

The LB1836M certainly can switch faster than 20KHz (outside the range of human hearing), but even at lower frequencies open-loop speed control behavior varies oddly at different frequencies and with different motors (big capacitors help smooth this out), so basically try and see. I don’t think you’re going to notice a huge difference in noise levels with the one of the Tamiya gearboxes though, the geartrain makes most of the noise.

So, what kind of robot are you trying to build?



In my experience, the LB1836 can just barely handle the motors in the small Tamiya gearboxes, and that’s with almost no load on the motors. For driving the little FA-130 motors, we recommend either our low-voltage dual serial motor controller or the low-voltage Orangutan, both of which are designed to deliver high currents at low voltages (e.g.3-4.5 V).

One thing to keep in mind is that 50% duty cycle at 200% voltage does not give you the same power since power scales with voltage squared. When you double voltage, you get 4 times the power, so limiting that to 50% will result in double the power.

I also recommend looking at Jim Remington’s Orangutan motor driver tests at

- Jan

Oh yeah, right. The power delivered is the thing that breaks the motor in the end.
Hmm, that’s odd. The motors are rated at 2-3 amps stall (not sure which, since several versions are in the motor’s datasheet) and the driver IC at 1 amp…

I bought the baby orangutan since it was small and it seemed there was no need for building my hbridges are using an IC. Then again, guess I was wrong and I’ll have to use it for something else…

Talking about the Tamiya gearboxes and their noises, how durable are they?
Shipping to romania ain’t cheap, eh… and ain’t quick, either. The whole package hasn’t arived yet, but I keep my hopes up :smiley: Although I believe i’ve seen motors in that shell for sale around here.

my robot - just something that can avoid walls for the beginning :stuck_out_tongue: I’m thinking of maze solving (the kind you draw on a paper, or maybe with led walls) in the big run for this guy.