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Originally Posted by billbo911
This thread got me thinking, ( I know, sometimes that can be dangerous) " How could I simply implement something like this with the hardware and software we already have?" Here is what I came up with.
In a nutshell, the EMF system is taking feedback directly from the motor during a period of "coasting" without any drive signal.
Why not add a small motor or generator, like an Micro RC car motor, to the driven axis and get feedback from it? The drive motor will turn the driven motor causing the driven motor to create a voltage/current source proportional to the speed of the drive motor. With gearing, and a little programming, this could be used in a closed loop feedback system similar to the EMF systems. This would negate the need to interrupt the PWM signal, sample the EMF value and then re-apply the PWM in our systems. We could do the sample and drive signal modifications in real time.
BTW, I know there are already motors available with tachometer circuitry built in. Many of these use optical encoders and put pulse trains out and some are strictly analog. Either design should be fairly "easy" to implement.
Thoughts???
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I am all for other sensors, especially if they are baked into the motors in the kit. I suppose that Chiaphua Motors (the makers of the CIM motor) would be willing to design in a cost effective quadrature encoder on the motor they sell FIRST if FIRST asked them. When I was with Delphi, I was AMAZED at how cheaply these guys could make a motor with very cool features (it was my research into finding a better motor supplier for Delphi's Power Sliding Door applications that got Chiaphua involved in FIRST).
One thing I don't like about this approach is that we are loading down the CPU. Eventually we will get to the point where interrupt load makes keeping track of dozen or so motors brings the MicroChip processor to its knees.
The Victors already have a brain onboard (as would most modern speed controllers). Given that, it would be nice to fob off some of the sensing and thinking required to implement closed loop motor control onto that remote brain.
Before folks object, Yes, I know that this would still require tuning and passing of parameters to get the PID loop to behave, but it would be a trade-off worth the cost.
I really think that FIRST could benefit from hiding the implementation details of feedback loops while making them standard operating proceedure of FIRST robots. We want FIRST robots to act like robots but we don't give folks the tools that robot designers have. Ask Copioli and other pros that design robots for a living: Closed loop motor control is a given.
Joe J.