[jhornbr225]

Hello All,

Longtime lurker, recently registered. I read this entire thread over the last week or so and can only say WOW.

Paul, you have made the difficult possible. You went from what seemed a complete electronic newbie, to a person who knows what they are talking about. (Because you've tried it!). Without your dedication, this open source project would have floundered, as many others have. Even though there were a few forks in eyes, and punches in the head, and naked Kim Jong. Your dedication and willingness to help others and the people who have ordered from you is incredible. It almost seems as if you have a unique connection to each controller out there, sending parts when needed, rebuilding others when needed, and continuous tech support, even to the point that if you don't know something, you find out the info, and pass it on.

The dedication of your family, with the long hours you manage to fit in, even with taking care of two children, job changes, moving out of the basement...etc., is amazing.

Also the base of knowledge from all the others who contribute to this project is amazing. The depth of knowledge in both electronics, programming, machining, etc. to make this project possible, has made this into a nicely polished project that is graspable for even a newbie.

I am a Controls Engineer, specializing in industrial controls and AC and DC drives. What you are building here rivals any commercial motor drive I have seen.

I do have one concern. With using the throttle to directly control the PWM into the power devices, you have basically set up a torque drive. In the applications I have seen, those that use torque drives are mostly winders, and Helpers.

Winders wind up some sort of material and the speed of the motor has to slow down, (or speed up) based on the diameter of whatever the material on the roll is. They are usually given a speed reference that exceeds the line speed of the material and then torque is limited based on whatever tension you want the material to wind up at. (Or Brake at)

Helpers usually are used for torque sharing. Same principles as winders. The helper section is given a speed reference based on the speed of the master section, then the helper itself adds to the speed reference. The current limit is then adjusted on the slave (Helper) to change how much "Help" the master section gets.

In both these applications, it is VERY EASY to overspeed the motor. If a coupling breaks, or the material that is being would up breaks, the motor basically, "Runs Away". Kind of like the apple tree incident.

Modern DC and AC drives usually incorporate multiple sections, each closed loop to get the desired motor speed.

1. Speed Loop. Receives Speed reference from operator to indicate desired speed. Also receives feedback from either a mechanical/optical device, or from Back EMF to indicate actual motor speed. The Mechanical/Optical device is preferred due to the fact the actual speed is indicated. Using BEMF does not account for the motors IR drop as load increases. If there is a difference between the reference and the feedback, an error is generated, and can be tuned with a PID Loop. The ouptut of this speed loop is known as speed error or current (Torque) reference, and is fed into the current loop.

2. Current Loop. Receives torque reference from speed loop, and current feedback. The difference between the current reference and the feedback drives the outputs sections to pulse motor whether it be IGBT's and a buss or capacitors in an AC drive, or an SCR to turn on and allow part of either a single phase or 3 phase waveform through (rectified so as to all be the same polarity) and fed to the motor.

What I'm getting at here, is that if you could incorporate a "Speed Loop" into your controller you would see many advantages.

You would probably not see the PWM runaway that you see when the pedal is requesting current and the contactor is not closed, so the PWM ramps to 100% quickly.

The speed of the motor would follow the pedal, regardless of the load, hills etc.

Ramp rates are based on speed RPM/unit time, not change of amps/time.

Cruise control could be activated.

What you have built here is an awesome torque controller. I feel that a little effort into adding a speed loop may pay off greatly in terms of driver comfort and ease of use.


Just my $0.02.

Either way, keep up the awesome work!

jhornbr225