Higher motor voltage?

[Dr John]

I am considering running the crumble motor driver chip (Texas Instruments DRV8835) with a higher voltage (9v) on pin 1 (motor voltage input VM ) than is provided from the crumble power.

This is an attempt to get faster motors for the drag race.

We have done this successfully on other robots using the L293D chip which is similar.

Can you pass on any hints or tips or suggestions? The data sheet suggests a 0.1 microfarad capacitor minimum. Thanks.

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[Dr John]

I have successfully applied this to our Crumble based Drag Racer.
With a 9 volt PP3 battery running the Crumble via a 7805 regulator, but with the Motor driver directly connected to the battery, we could get about 7.5 volts to the motors.
This is, of course, fully PWM controllable by the Crumble Pic processor, so we can steer down the line.

An extra 1500 microfarad capacitor across the crumble’s 5 volts did help matters.

About 45% faster!

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[Dr_Alex]

Nice mod, can you post a circuit diagram?

[Dr John]

There’s not much of a circuit. The 5 volt track to the motor driver chip needs to be cut, then cleaned each side of the cut.

Then I soldered a wire to the track each side of the cut.

The wire nearest the driver chip is then connected either to:
– the original 5v line (the other wire), for normal operation.
– a 9volt supply. For faster motors.
I will post an image of which track to cut.

[Dr John]

Smaller image file….

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[Dr_Alex]

Thanks for that. In the first picture you posted, to me it looked like a component was added next to the motor controller, but now I can see it was just the header pins you had soldered in for connections!

I was wondering if the current is still limited to 1.5 A. I pressume it will be, as from the data sheet it says it is internally overload protected. Does the chip need a heatsink though, when running with the extra voltage?

[Dr John]

Not sure.
We’re running pololu 30:1 motors with 60mm wheels. At the higher voltage we get a micromouse Drag race speed of about 2.2 seconds. (for 5.65 meters)

Current (9 volts) to 1 motor (stalled) = 1.1 amps Not stalled = 0.68 amps.
At the 5volt setting it’s about 0.23 amps.

No trouble so far Fingers crossed.

[Author]

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