Paul & Sabrina's cheap DIY 144v motor controller

[MPaulHolmes]

New feature added! Gentle Ramp up of throttle. There's a problem if you accelerate too fast from 0 RPM. A motor has about 0.01 Ohms of internal resistance, or even as small as 0.001 Ohms for a really big one. Also, the inductance is very small, like 60 uH or so. The inductance resists a change in current, which is helpful in current limiting. However, 60 uH is TINY! A worst case senario can see a 4 amp increase in a millionth of a second! So, it's tough to limit the current when it's growing so fast. So, one thing you can do is restrict the rate of growth of the PWM duty. For example, if you ram the gas pedal to the ground almost instantly, the software will make you wait like 5 or 10 seconds or whatever until it reaches 100% PWM duty. It doesn't limit how fast you can slow down, though. It is tested and working.

That buys me some extra time to monitor the current increase and shut things down if the current gets to high.

I still have about 91% of the space on the chip available! ya! Maybe I'll add space invaders if there's not much else to do.

[Intrigued]

Originally Posted by MPaulHolmes

I still have about 91% of the space on the chip available! ya! Maybe I'll add space invaders if there's not much else to do.

Hey, have a little fun, and make the spaceships go vertical, and let them be the battery voltage sensors, a la the LED bargraph battery monitor, and then have your gun start shooting when the batteries reach their lower limit!

[MPaulHolmes]

I'm going to use that. That's good... That's really good. It gets boring driving sometimes. It would be awesome to have a video game built in to the battery monitor.

Update: My wife and I got a junky dremel from harbor freight that wobbled like crazy, so we returned it, and got a DREMEL® from Lowe's, with a diamond tip fine engraving thing and a slightly bigger non-diamond engraving thing. I'm using them to etch the 5 ounce (of copper per square foot) PCB that came in the mail today! bam! MOst people buy a weird solution of strange liquid and let the copper sit in it for a long time, but my baby would drink that.

The already etched one is a practice 1 ounce pcb from radio shack.

[Intrigued]

Neat! Boy, I hope you use heavier-duty parts than the ones they used in those Logisystems controllers that kept blowing out the backs of the cases. By the way I'm reading some of the blogs on them, I'm wondering if that wasn't a problem with not having a good pre-charge resistor in place...???

[MPaulHolmes]

I almost bought a logisystem controller. I guess I'm glad I didn't now! I'll have quite a bit of safety margin built in to the car version. Lots of mosfets to keep things way under specs.

[MPaulHolmes]

I've added current limiting to the software. So, now I can choose any max current, and it won't go above that. This will be good for testing what the max current should be.

I also etched the power section on the 5 ounce PCB. It's way thicker than that ghetto stuff from radio shack! holy cow! The dremel did a pretty good job. I think a mill might work a little better, but still this is a good cheap solution.

[Intrigued]

Hey, it don't have to be pretty to work! You should have let the person that did those thumbnails do the work!!!

Is that a sim farm game going on there in the background???

Hey, I just thought of something you might be able to use for a mill. Find a mom 'n pop sign store in the area, (or on eBay) and see if you can get your hands on an old sign scroll, or mill, or whatever they call them. You know, the things they use to etch those plastic signs that say "MEN" and "LADIES".

...or is that what you already had in mind???

[MPaulHolmes]

It's a farm game on facebook. You buy seeds and animals, and then harvest stuff so you can buy barns and chicken coops and stuff like that. I'll check on your idea about the mill. It doesn't have to be the usual 1.5 HP or whatever. Just something that can cut a thin layer of copper in a straight line.

[Intrigued]

3 AXIS CNC MILL / ROUTER Machine - eBay (item 220330237263 end time Jan-14-09 01:19:59 PST)

...now that I've already posted a couple of these on your VW thread, how about something like this???

[MetroMPG]

Paul & Sabrina: you amaze me. (Well, anybody who's not slow at projects, like me, amazes me.)

A thought after seeing the temp protection circuit: you might want to ramp up the current when exiting thermal protection cut-off. Same if you incorporate low voltage cut-off.

I've hit the low voltage protection feature with the junk batteries we first had in the ForkenSwift, and it was pretty violent: First gear, going slowly up a little hill, controller cuts current, car coasts to a stop. Foot still on throttle, pack voltage rebounds above the threshold, car jerks forward. Pack voltage falls, controller cuts current, car stops. Pack voltage rebounds, car lurches. Stops! Lurches! Stops!

Just a thought. Either that, or incorporate a high pedal safety feature that gets checked any time the controller goes from 0 current to some current request.