Paul and Sabrina's Cheap 3 Phase Inverter (AC Controller) with Field Oriented Control

[e*clipse]

I've been trying to think of a way that this could be done without putting a bunch of cumpooter stuff in between the driver and the vehicle.

I think some safety parameters such as a "max rpm" in the motor controller would be a good start, whether or not this double motor idea is used. It could be derived from the motor frequency data, and really wouldn't matter what the other motor is doing. (just for a safety limit) More advanced code could provide traction control - which of course would be regen ABS!

I love the cutting brake concept. I've been trying to think of a way the steering position could be used without adding a bunch of microcontroller code complexity.

One idea is this: a simple analog circuit that would allow a driver to balance the throttle input. It could be a circuit where one input is the throttle, a second input determines the balance of the two outputs. each output goes to a different motor controller. Now, this could be adjusted on the fly, either by the driver or some mechanism that senses steering position.

I'll bet it could be as simple as two op-amps set up as differential amplifiers; they both get the throttle input for one input and a different bias input depending on the balance signal. All this could be implemented with extremely reliable mil-spec hardware and a bypass switch if things go awry.

In an AWD setup, the driver could even balance the fore/aft torque balance while steering position, relative motor speeds, or an accelerometer adjust left-right torque balance. Rally race car drivers would be jealous.

-e*clipse

[freebeard]

It could be handy wherever there is slippin' and slidin' involved. The tie-in to the steering was to put the idea over the top.

Regular sand rail cutting brakes started as two levers slipped over the regular hand brake so you could pull one or the other cable at a time. They evolved to a single upright lever that is forward for left and back for right, that I believe is hydraulic FWIW.

[Cyruscosmo]

Originally Posted by Astro

Because the throttle is commanding torque is there a possibility of the spinning wheel RPM increasing to dangerous levels as the controller tries to bring the torque up to the requested level? Not easily achieved on a slipping/spinning wheel. I am thinking of one wheel on ice sort of situation. Even in a single motor situation on ice would the controller keep the rpm under control?
This is just a theoretical question for me, living in Australia the only ice i ever see is in my drink.

That is pretty much what happens with an ICE powered vehicle. One wheel slips and since the engine only has a gas pedal for input the RPM goes up. The driver knows what is up and releases the gas pedal, if not the engine can grenade or in the case of a rev limiter it just hovers at it's top RPM range.

Unless you were trying to make some form of traction control there would be little reason to do anything but back off of the throttle. Even with an electric motor the RPMs are unlikely to climb so fast that it catches you by surprise. Unless you were dumb enough to push in the clutch and not release the throttle in which case either ICE or electric would do the same thing. Boom

And besides I thought the controller already had a rev limiter built in?

Traction control would be nice and since most new vehicles already have anti-lock sensors at each wheel getting feed back for the RPM of each wheel is pretty straight forward. But you still need a way to get power to the wheel with a grip on the road and make the other stop spinning.

I would just install a Detroit locker, or an air locker, or power lock or some other form of mechanical traction device and just drive flat track style. Driving a vehicle in adverse conditions without the proper gear is asking for trouble anyway. You should see all the dorks here in the NW trying to deal with what little snow we have.

Cyruscosmo

[Cyruscosmo]

Originally Posted by e*clipse

The basic "open" differential is really a torque split device that is supposed to evenly divide the available torque between the left & right wheel in a corner. The speed and speed differential is not important. This all works fine, until one wheel looses traction, and all the torque goes to that wheel.

So, now look at the simple dual AC motor drive setup: Again, the torque is evenly split between the left & right wheels, as requested by the throttle. In a corner, that is just fine, as the speed & speed differential don't matter. If one wheel looses traction, it is actually BETTER than an open differential, as the wheel with traction will still get its proportion of the torque.


Thoughts?

- e*clipse

First thought that comes to my mind is powering into a corner with both wheels trying to do the same speed independent of the other. If the steering is compromised in any way you will go where the motors tell you to go which is straight. Think tank type steering.

A traction device in a differential is the way I will go over trusting any form of code to get it right. All you need is one bad rainy day and you could spend the rest of your life in a wheelchair or worse.

Now that being said I know there will come a day when wheel motors will be the new thing and the control devices will get so good that the mean time between failure is a moot point but why make something that complex when a simple mechanical device will do it right now the right way every time.

Use the sensors already in place to manage wheel spin or Rev limit the electric motors so they don't blow up when a wheel slips and simply let go of the throttle.

Cyruscosmo

[e*clipse]

Originally Posted by Cyruscosmo

First thought that comes to my mind is powering into a corner with both wheels trying to do the same speed independent of the other. If the steering is compromised in any way you will go where the motors tell you to go which is straight. Think tank type steering.

A traction device in a differential is the way I will go over trusting any form of code to get it right. All you need is one bad rainy day and you could spend the rest of your life in a wheelchair or worse.

Now that being said I know there will come a day when wheel motors will be the new thing and the control devices will get so good that the mean time between failure is a moot point but why make something that complex when a simple mechanical device will do it right now the right way every time.

Use the sensors already in place to manage wheel spin or Rev limit the electric motors so they don't blow up when a wheel slips and simply let go of the throttle.

Cyruscosmo

The important thing here is that it is NOT a speed control issue. This makes the whole thing significantly different than attempting to match the speed of two independant motors. In fact, from a controls perspective, speed control requires another complete control PID loop. So with only torque control the motors won't be fighting you like tank steering. If things go really awry, one motor may produce 25% more torque than the other, but this is much different than the fight that could happen when one motor tries to go 25% faster than the other. In that case, the control loop may command FULL torque until the speeds match, or negative torque on one motor with increased torque on the opposite - which could have awful results like you are warning about.

I too am leary about putting too much computer (code) between the driver and control. This is why I'm trying for a simple analog circuit with a bypass switch. The bypass switch would make the commanded TORQUE from each motor identical.

I'm not completely convinced locker differentials are a simple solution. Putting one in an MGR would be a very expensive custom job.

When I was growing up, my dad had a Chevy Malibu with a "limited slip" differential. We went skiing every opportunity, and I can say my dad's excellent driving made up for the differential's weird behavior. If one wheel slipped, it would clutch and force all the torque to the opposite wheel, which could slip because it all off a sudden got all the torque. Then it would clutch to the opposite side. Back & forth, fishtailing down the road because of the "help" from the differential. According to a friend with lots of off-road experience one needs to be very careful with locker choice, because the on-off behavior is pretty common.

[Cyruscosmo]

Originally Posted by e*clipse

The important thing here is that it is NOT a speed control issue. This makes the whole thing significantly different than attempting to match the speed of two independant motors. In fact, from a controls perspective, speed control requires another complete control PID loop. So with only torque control the motors won't be fighting you like tank steering. If things go really awry, one motor may produce 25% more torque than the other, but this is much different than the fight that could happen when one motor tries to go 25% faster than the other. In that case, the control loop may command FULL torque until the speeds match, or negative torque on one motor with increased torque on the opposite - which could have awful results like you are warning about.

I too am leary about putting too much computer (code) between the driver and control. This is why I'm trying for a simple analog circuit with a bypass switch. The bypass switch would make the commanded TORQUE from each motor identical.

I'm not completely convinced locker differentials are a simple solution. Putting one in an MGR would be a very expensive custom job.

When I was growing up, my dad had a Chevy Malibu with a "limited slip" differential. We went skiing every opportunity, and I can say my dad's excellent driving made up for the differential's weird behavior. If one wheel slipped, it would clutch and force all the torque to the opposite wheel, which could slip because it all off a sudden got all the torque. Then it would clutch to the opposite side. Back & forth, fishtailing down the road because of the "help" from the differential. According to a friend with lots of off-road experience one needs to be very careful with locker choice, because the on-off behavior is pretty common.

First I should say that I do not yet understand enough about electric motors and there respective behaviors. I have been a gear head far longer and only have those examples to fall back on with only a few years actually hands on with electric cars. If you were to put two ICE's back to back and run there outputs through a gear reduction and then out to one wheel each you could effectively steer the car by throttle alone. It may not work like a tank where one gear set has a brake to stop it while the other runs on but it would work to an extent.

Rather than mess with code for two controllers with motors driving two separate wheels I would simply connect both sides together with a differential. Front to back would not be too much of a problem as long as the front wheels were setup to outrun the back by a little.

By “simple” I mean gears, electronics and code are not simple to me, they are more like voodoo. There is a device that is called The Gleason Torsen. Gleason's Impossible Differential I know at least three people who run these and have nothing bad to say about them.

My old 69 Ford has a Detroit locker in the rear and a power lock in the front. When I get on the throttle hard I may as well have two solid axle drives. With a 460 the usual behavior on dry roads is a thunk and then clicks when I go round corners. It has never caused any handling problems and in snow and rain you can not even hear it when one or the other dog clutches overruns and disengages. Mostly used for camping and off road fun I have driven it for over 20 years.

When I get hold of one of those MGR's I will disassemble it and take the spool to my buddies shop and see what kind of traction device will work in it. He runs NW differential which specializes in running gear repair and up grades.

Yes it is true and that can happen but what a lot of people did not know with the limited slip differentials is that they “required” a special additive to keep the components from chattering and causing that problem. The other differential device Chevy used worked with a set of spinning weights. When one axle over ran the other it caused the spiders to lock. I never did like driving those because they did weird things.

Cyruscosmo

[freebeard]

If you were to put two ICE's back to back and run there outputs through a gear reduction and then out to one wheel each you could effectively steer the car by throttle alone. It may not work like a tank where one gear set has a brake to stop it while the other runs on but it would work to an extent.

Wouldn't the electric regeneration correspond to a gas engine on trailing throttle, or a diesel engine with a Jake Brake? Tanks, of course, can reverse one tread.

At Ft. Lewis in the 60s I saw a 50-ton tank jam on the brakes. The Cg rose up to ~12ft in the air and it ran on those little angled sections of track at the front, then settled back down when it stopped.

[e*clipse]

Originally Posted by Cyruscosmo

If you were to put two ICE's back to back and run there outputs through a gear reduction and then out to one wheel each you could effectively steer the car by throttle alone.

By “simple” I mean gears, electronics and code are not simple to me, they are more like voodoo. There is a device that is called The Gleason Torsen. Gleason's Impossible Differential I know at least three people who run these and have nothing bad to say about them.

When I get hold of one of those MGR's I will disassemble it and take the spool to my buddies shop and see what kind of traction device will work in it. He runs NW differential which specializes in running gear repair and up grades.

Yes it is true and that can happen but what a lot of people did not know with the limited slip differentials is that they “required” a special additive to keep the components from chattering and causing that problem. The other differential device Chevy used worked with a set of spinning weights. When one axle over ran the other it caused the spiders to lock. I never did like driving those because they did weird things.

Cyruscosmo

Makes perfect sense to me.

I guess I'll have to say what I'm proposing is definitely experimental and NOT for the average driver who can barely handle a manual transmission. This car will be running a dual master cylinder, no power brakes setup and a "Miyata" mod manual steering setup as well. I'm going to spend a lot of time in gravel parking lots and maybe even the local dirt track before I begin to trust it. After I am able to tune it to neutral behavior, I'm going to play with that steering effect - I think that could be extremely positive. Think about autocrossing or driving the car at the traction limit with the power HELPING you through the corner.

I do really like those Torsen differentials. In fact, I have one waiting to be installed in the front of my truck. I'm trying to find one for the rear as well.

I'm having a meeting with our local drivetrain guy to see about spooling the MGR and what half-shaft options I have. It's funny, when I was describing this project, he said "You're not doing some weird military thing, are you?"

I'm very interested what your buddy has to say about this. Would some pics and dimensions of the guts (specifically the differential) help?

-e*clipse

[freebeard]

Think about autocrossing or driving the car at the traction limit with the power HELPING you through the corner.
...

I'm having a meeting with our local drivetrain guy to see about spooling the MGR and what half-shaft options I have. It's funny, when I was describing this project, he said "You're not doing some weird military thing, are you?"

...or negotiating muddy trails or maintaining traction on an unforgiving surface like dried salt.

Tell him it's for the Zombie Apocalypse.

[MPaulHolmes]

I got the flywheel attached, cyrusCosmo! It works great. I have never been very mechanical, but finally understand what you guys were saying about connecting a DC motor and doing regen. I could use the same battery bank to power the dc motor, and then run the AC motor in regen, charging the same battery bank. haha. I'm not going to, at least at the moment, as I don't have a Dc motor.

I tested the battery current limiting, and it seems to work. You can set it to take no more than 'x' amps from the batteries, and separately, no more than 'y' amps into the batteries. That is a separate control from setting the max "motor amps" (line to line amps). I'm going to just send out the controllers to the 2 beta testers, and worry about polishing the details from a distance. I think it's at a place where the fundamentals are good. So, adding the brake regen feature will have to be added on later. I don't have a way to test that at all at the moment. I'll just send it with the wig-wag throttle. You can set the regen territory to be any amount you want, so it could just be the small amount that we were talking about that causes the car to feel like it slows down a bit when you take your foot off the throttle.

It will be interesting to see how the PI loop tuning goes. For now I'll make a separate C file for that, that will need to be run in debug mode with a locked rotor (emergency brake on?) at a relatively low voltage (48v??). I could do it all as a config mode in the same software as the regular C file, but I'm just trying to keep things simple at the moment.

So, I just need to test the UART and EEProm stuff, and then I'll get the stuff together and ship them out. I hope you guys didn't pay for shipping already. haha. If so, then it will get shipped out in about 2 weeks (payday). haha