Paul & Sabrina's cheap DIY 144v motor controller

[Frxdy]

Originally Posted by MPaulHolmes

I just about finished soldering the control and driver board for the 1000amp controller and the control board, l

Pictures! Pictures! *smile*

I've been a lurker, but recently have ordered parts and am going to see about building the 500 amp controller. Over the last week or two I have been reading this entire post. I'm up to page 350 right now. I figured I'd better start posting as I think I need to have some input before I can post photos & stuff.

One comment: Someone asked about building their own power board from 16oz (roofing) copper and using fiberglass or carbon fiber to separate them. Well, two things: One: You can't use carbon fiber. It conducts electricity!! Two: If you use fiberglass and epoxy resin you will need six layers of 6 oz. fiberglass to get about .06" of thickness. (I say this because I know for a fact that 2 layers makes .020".)

OK, back to our regularly scheduled show.

[pamcmills]

In response to electricstorm, I'm also using a forklift motor in my S-10. It's a GE motor a little over 11 inch and in the 200 pound range. Except for the spline shafts and different bolt pattern on the output side, It looks exactly like the NetGain Warp 11 motor. The motor was rated 13 hp @ 48 volts, 150 amps, 1800 rpm, class H insulation. Class H insulation is good for up to 356 deg. F and 600 volts or so. Generally the type of brushes in that motor are only good for about 78 volts. But I have been running 144 plus volts for 10000 miles and have noticed no abnormal brush ware. I did set my brush timing to 6 deg advanced to reduce brush arcing which works for my motor with the load it's under. Hope this was helpful.

[jyanof]

I wanted to throw this out there and see what ideas you all have.

This all started when a buddy created a motor and vehicle model (mathematical) and tried to predict the acceleration performance of his future EV. I suggested we plug in the parameters for my vehicle and see how the predictions match reality.

It was pretty far off though - It said I should be in first gear for only a few seconds whereas it took nearly twice as long to accelerate to shifting speed.

So, i logged some data from the serial port to investigate what the controller was actually doing. Turns out that I was getting about 375A to the motor, despite flooring it, and we had assumed that the controller would be maxed at 500A.

I had set the kp and ki values for 'smoothness' and that resulted in a pretty slow control loop. consequently, the motor speed accelerated faster than the control loop could keep up. By the time it set a new PWM duty cycle, the motor speed had increased and the new PWM value isn't enough to maintain the commanded motor amps.

Increasing both kp and ki makes the control loop faster and I reached a point where I could maintain about 470A during acceleration. I even went too high at one point and the controller immediately went into hardware overcurrent protection with a slight press of the pedal.

However, as the loop speed increased, the 'smoothness' decreased. If I was at a dead stop with a little bit of slack in the gear train, the motor current would shoot up quickly and result in a jerky start that led to slowly damped torque oscillations. Also, abrupt changes in throttle position resulted in torque oscillations due to the elasticity in the geartrain, particularly in 2nd gear.

Has anyone else observed this? For the most part, this isn't necessarily a racing controller, but it might be nice to find a way to have the best of both: fast control loop for fast accelerations and a slower loop during start or cruising the parking lot.

The only idea I had was to allow for Kp and Ki to vary with some other parameter, maybe throttle position or PWM dutycycle. Any other ideas?

[adamj12b]

Originally Posted by jyanof

I wanted to throw this out there and see what ideas you all have.

This all started when a buddy created a motor and vehicle model (mathematical) and tried to predict the acceleration performance of his future EV. I suggested we plug in the parameters for my vehicle and see how the predictions match reality.

It was pretty far off though - It said I should be in first gear for only a few seconds whereas it took nearly twice as long to accelerate to shifting speed.

So, i logged some data from the serial port to investigate what the controller was actually doing. Turns out that I was getting about 375A to the motor, despite flooring it, and we had assumed that the controller would be maxed at 500A.

I had set the kp and ki values for 'smoothness' and that resulted in a pretty slow control loop. consequently, the motor speed accelerated faster than the control loop could keep up. By the time it set a new PWM duty cycle, the motor speed had increased and the new PWM value isn't enough to maintain the commanded motor amps.

Increasing both kp and ki makes the control loop faster and I reached a point where I could maintain about 470A during acceleration. I even went too high at one point and the controller immediately went into hardware overcurrent protection with a slight press of the pedal.

However, as the loop speed increased, the 'smoothness' decreased. If I was at a dead stop with a little bit of slack in the gear train, the motor current would shoot up quickly and result in a jerky start that led to slowly damped torque oscillations. Also, abrupt changes in throttle position resulted in torque oscillations due to the elasticity in the geartrain, particularly in 2nd gear.

Has anyone else observed this? For the most part, this isn't necessarily a racing controller, but it might be nice to find a way to have the best of both: fast control loop for fast accelerations and a slower loop during start or cruising the parking lot.

The only idea I had was to allow for Kp and Ki to vary with some other parameter, maybe throttle position or PWM dutycycle. Any other ideas?

Hey Joe,

Ive seen this before.

When the controller was early development I was testing it in my golf cart. Since its a direct drive to the diff, you could feel everything.

When held on a hill just by stalling the motor, you can feel it pulsating the current. I would hold it on the hill like this to work at tuning the loop. I was going for the current to track throttle perfectly. Once it tracks perfect, the pulsating pretty much goes away.

Here it is while oscillating:

https://www.dropbox.com/s/odjoxu2kwm...%20Shudder.png

and here it is after perfectly tuned:

https://www.dropbox.com/s/7fbxmdev3a...27.41%20PM.png

and another:

https://www.dropbox.com/s/156arxi60h...33.47%20PM.png

See how the current feedback(CF) tracks throttle position perfectly?

Does this help at all joe?

-Adam

[jyanof]

Originally Posted by adamj12b

Hey Joe,

Ive seen this before. ..

See how the current feedback(CF) tracks throttle position perfectly?

Does this help at all joe?

-Adam

it is possible that i need to figure out a better combination of kp/ki to tune the control loop.

but, what i'm getting at is that it's also possible that a loop tuned at a single point may not be suitable for all operating conditions, particularly those at the extreme ends. in this case, i haven't found a single setting that works well for both low speed starts (particularly when there's slack in the geartrain) and high acceleration rates in 1st gear.

[bennelson]

I've noticed that there ARE times when I would like to have at least two different settings on the controller.

Just one example.... Last year, I had my car in the local Independence Day Parade. The whole trip was at walking-pace or less. A really hard speed to keep steady. My controller was tuned for smooth starts and brisk acceleration, but didn't handle going back and forth between 0 and 1 mile per hour all that well. (I did do a burn-out in front of the review stand though!)

By the end of the parade, I decided that if I was ever going to run in a parade again, I would tune the controller for speed and acceleration that would be more suitable. (And remember to write down or save those parameters!)

In fact, the new generation of commercially-built EVs have features similar to this. In the Chevy Volt, you can choose between a NORMAL and SPORT mode at the push of a button. Essentially, SPORT mode tells the computer to allow for a little more aggressive throttle response and higher amperage from batteries to motor. It's a great feature. The Volt is a lot of fun to drive in SPORT mode.

[MPaulHolmes]

If you can figure out certain tell tale points when Kp and Ki should transition, it would be very easy to change it in code. Even have some sort of continuous function that has kp and ki as its outputs depending on various inputs like pwm duty and current feedback.

[jyanof]

Originally Posted by bennelson

I've noticed that there ARE times when I would like to have at least two different settings on the controller.

Just one example.... Last year, I had my car in the local Independence Day Parade.

Exactly! and so, for me at least, there are normal every-day occurrences that are like parade mode - creeping up the driveway, pulling out of a parking space, picking up crap food in a drive through... It'd be nice to have optimized operation at those times AND during brisk acceleration.

Originally Posted by MPaulHolmes

Even have some sort of continuous function that has kp and ki as its outputs depending on various inputs like pwm duty and current feedback.

this is kind of what i was thinking. it seems that all of the the times where a slower loop would be good occur when moving slowly (parking lot, driveway, etc) and only lightly pressing the pedal. thus it seems like throttle position might be good to use as the input. i don't think the other parameters are that indicative of moving slowly. oh, and i bet there's a lot of processing time available when the throttle position is processed.

maybe there could be 3 more settings. a different Kp and Ki value at low throttle positions and a value that represents the pedal position at which the settings change (could be 0-99 for percent throttle position).

i don't know if it's good to have a step change for Kp/Ki, so maybe the kp/ki values change linearly from the new values at zero throttle position to main values at the change-over value. above the change-over value, only the main kp/ki values are used.

then, the tuning process could be: tune the loop for low speeds using the main kp/ki settings and write them down. then, re-tune for brisk acceleration. lastly, set the low throttle kp/ki values from the values written down and play around with the changeover point.

thoughts?

[dave koller]

I just do something stupid -- and switch a resistor in the throttle circuit....

[electricstorm]

Thanks to everyone who responded to my forklift motor question.

To pamcmills, I have a 2002 Geo Storm and a warp 9 will just fit in the area that the motor used to sit in. It seems like all the forklift motors are larger than that. Could be wrong though. Still looking around.

Jim