Selection of a brushed controller for long, sweeping turns on a tank-style robot

4 years 9 months ago #29531434 by andyBaker
Hello,

I was wondering if anybody might be able to assist me in selecting an appropriate brushed controller for a project here at our shop. I'm currently using the obsolete AX 3500 controller. It barely gets warm during operation. I'm happy with it in that respect.

I currently have a "tank control" style base - Motor on the left and motor on the right which was originally a wheelchair base. The motors are robust and in excellent condition, and have been fitted with encoders (360 PPR X4 because of the quadrature) and all signals are verified good on the oscilloscope. It's hooked up as closed loop speed control, and I've done a bit of tuning to the PID loops and it's about as dialed as I feel it can get, or even needs to be. It's a 24V system, and as an RC car, it's a lot of fun and runs great. BUT... we don't need an RC car.

My problems is this - The steering is TOO FAST. I've set the input to Exponential already, and to slow it down a bit, I expanded the pulse width range on the steering channel RC input (in the RoboRun software), and while that all works in theory, I'm losing a LOT of resolution since as far as I can ascertain, the RC signal is converted to an 8 bit value, and my method only ends up using a small portion of that range, leading to maybe a dozen or so discrete steps of "turn" making any kind of long sweeping turn nearly impossible. What I really need is a way to adjust the gain of the steering within the mixing algorithm so I can get sub-percentile differences in wheel speed to allow these long sweeping turns and precise control, which is why I fitted these encoders.

In short, I'm looking for a controller that has better control over the mixing, since the current controller is more than happy to execute a high speed death-roll and nothing less when I give a full-turn command.

Our purchase time-frame is immediate.

Thank you!

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4 years 9 months ago #29531435 by niko
The mdc2230 and mdc2460 are the recommended replacements for the ax3500

The motor aand battery connections are identical. The 15 pin connector is practically the same. A more robust connector is ised for the encoder interface

Commands are converted to a +/-1000 value so that is practically 11bit of resolution.

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4 years 9 months ago #29531443 by andyBaker
Hello - Thanks for that info. I'm looking at the manual for the mdc2230, and everything looks upgraded, but the part on the three different mixing modes is pretty vague and the spreadsheet that explains them isn't really all that great. Is there a more user-friendly explanation of what those modes mean?

Thanks!

Andy

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4 years 9 months ago #29531445 by niko
Hello Andy,

Please advise the user manual, chapter "Mixing Mode Select", in page 75. They are typical mixing modes. which caan be used according to the setup. We would advise to try them in you set-up in order to make sure what is more suitable for you.

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