Quote:
Originally Posted by jhersh
I'm interested to better understand what features you are interested in here. I found very little detailed documentation about what this does technically. What op amp are you referring to?
This sounds like a request that would need to be implemented in the motor controller directly. For a controller like the Victor, there is a relatively long time that the H-Bridge will be driven after the incoming servo PWM signal stops. The Servo PWM is also not necessarily synchronized with the H-Bridge PWM. I'm not sure what op-amp it is that you keep referring to.
I'm interested in following this up. Please give more information.
Thanks,
-Joe
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For the gyro, due to DA not working entirely in the analog domain, the digitization quanta can hide/diminish/interfere with measuring small amounts of rotation. To compenstate, many gyros have adjustable analog amplification that amplifies the analog voltage via an operational amplifier. Think of it a voltmeter autorange feature, but under program control. You need to do this at the analog level before A/D conversion. The drift compensation is different - it compensates for drift of the gyro h/w output.
The tail rotor gyro referenced splices directly into the tail pwm signal and by adjusting the gain and setting the mode to heading lock, you can get the helicoptor to fly straight without having to constantly compenstate.
For the back-emf, this isn't typically implemented in the H-bridge. Usually its implemented at the source where the PWM signal is generated. When you idle the speed controller and don't output any drive voltage, the motors free spin and act as a generator. A measurement of the back-emf voltage is in direct correlation to the motor speed. Doing an analog pre-charge capture at this point in time allows you to measure the back-emf and thus speed of the motor. Often the motor voltage is higher than the A/D capture range and so a resistor divider is used. Due to digitization quanta, analog amplification is used to auto-range so you have better measurement of low speeds (voltages). You can do some of this programmatically, but you have to set the PWM to idle, wait some small but finite amount of time for the signal to propogate out, sample the back-emf voltage, and then restore the PWM value. The measured back-emf is often used in PID feedback loops for motor control. Its especially useful for smaller motors where quad encoders would be overkill. Also, its real easy to detect motor stall as the back-emf voltage drops to zero during stalls. This also means its relatively easy to quesstimate the amount of current being drawn by using both the value of pwm and the measured back-emf.