Hot-rodding the Toyota MGR

[Cyruscosmo]

Originally Posted by freebeard

So, PLA to ceramic to metal inhouse, then off to NorCal for the touchup machining?

What do you plan to make with a ton of aluminum?

The Aluminium was collected originally for the raw stock to cast the cases. We were making an automatic trans-axle for applications such as Bugs or ground up custom jobs like the Ariel Atom. There are a few kit makers that offer skeleton cars that you add the parts you want to them. Electric trans-axles would fit right in there.

The C4 was chosen for the two clutches and two bands. Building a case for the guts of a C4 would be a snap and ford made the things from 64 to 89 so there are millions of them out there. The C4 also has a very wide range of after market parts available for street and strip racing. They can reliably handle up to 300 HP stock and over 600 with modifications. With the addition of a computer controller like an Arduino or PIC or whatever your flavor is you can make it shift as hard or soft as you like and set the ranges to compliment the motor you use. They would also be offered for DC motor input like the advance dc 9 and so forth.

The differential is out of a Subaru. The unit is very compact, there are numerous after market dealers in high power parts and there are millions of them and they can handle roughly the same HP numbers as the C4.

They would all have the variable pump for cooling lube and power steering, brakes and in some cases windshield wipers.

So three kits were in the works.

First was a motor hydraulic pump only version for installation on the bell housing of whatever you like. This kit would cover the front wheel drives. Or conventional.

Second was a motor/transmission kit for installation in applications where the owner wants an automatic. This would bypass having to modify the stock automatic for use with an electric motor and keep the use of the stock controls. This was for the " I want to convert my car to electric but my wife can not drive a stick" crowd.

Third was the trans-axle version for the mid engine rear engine crowd. Two trans-axles for AWD or with the addition of the output shaft from the Subaru trans-axle you could go AWD with a drive line going forward. Think AWD dual motor in something like a Z3.

All were to be kits that used parts from already established donor assemblies I.E. Ford C4 and Subaru.

But things change and when my friend passed away a couple years back I decided to build my own shop and build a couple units for the vehicles I drive and see if there was any interest. He had all the design tools and CNC machinery.

Anyway it depends on how things work out.

Cyruscosmo

[e*clipse]

Here's what I don't get: Why do you need to shift gears at all?

Seriously - the rated speed with this motor is 10,500 rpm. Along with the stock 6.86:1 gear ratio and average sized tires, my calcs (and others) indicate that this is good for 115 mph. Now, 50kW may not be enough for that speed, but this is a power issue, not a transmission issue.

This is why I'm going for a two motor system initially. If spec'd with the correct battery, the car can easily handle normal driving conditions. Accelleration is reasonable, at about 8 or 9 seconds 0-60.

Would this be improved with a transmission? Not according to Tesla, who built the first Roadsters with 2 speed transmissions. Because of reliablity issues, they simplified to a single speed gearbox and re-tuning the motor.

I'm totally into the idea of a custom gearbox, similar to the MGR - just one that's a bit better suited for EV use.

[e*clipse]

OK, this kind-of more on topic for the thread.

I started out saying we need to find a better way to cool it, because if we push it harder it will produce more heat. But it was all vague.

Well I've gathered a bunch of seemingly unrelated info from those ORNL test and the motor design papers I previously posted.

Also, I found a paper about how much current you can push through motor windings. This paper gives an excellent overview of how windings fail from both overcurrent and circulating currents at high frequencies.
http://www.smma.org/pdf/conferences/...%20Density.pdf

I based this hand-waving analysis on close equivelencies and similar designs. Unfortunately, there is no ORNL test of the MGR directly.

So, as a start, here is some technical info about the MGR.
1) each phase leg is made of 12 0.032" diameter wires.
2) rotor diameter: 14.79 cm
3) rotor laminate width: 4.57 cm
4) stator has 48 slots
5) motor has 8 poles

Interestingly, this is very similar to the 2010 Prius. The winding use the same gauge wire and have 12 in parallel. The motor is also uses a 48 slot 8 pole stator. The rotor is slightly smaller in diameter and length, so it's not a 1:1 comparison.

Other motors reviewed in the ORNL tests include the 2008 Lexus 600h and the Camry, which use different wiring and rotor dimensions, but still use the 48 slot 8 pole design. All of the new Toyota hybrid motors us a design similar (with different dimension) to the one in the paper detailing the 2005 SUV. Interestingly, that paper is actually talking about MG2 used in the Highlander hybrid.

So, I wanted to find some reasonable limits to the current this motor could be pushed to. The ORNL tests go WAY beyond just parroting the OE specs. Everything including thermal behavior (with a whole bunch of extra thermistors) and magnetic field strength are tested.

First, they did a series of tests to measure the BEMF. The tests were conducted to well over 12500 rpm. For the Prius, the test was run up to 14000 rpm! Considering that the MGR's rotor is the same design with a smaller diameter, it says to me that the MGR should be very capable of running the same speed - MUCH faster than Toyota's 10,500 rpm limit. Also, BEMF - measured as Line - neutral RMS was completely linear. For the Prius it is 450V @ 12000 rpm. The Lexus LS 600h produced 300V BEMF @ 12,000 rpm.

Next, they did a number of locked rotor tests to determine torque for the amount of current. The MGR's stator windings are almost identical, but since the rotor is smaller, the torque numbers won't be usable. The current limit for the locked rotor torque was based on the stator winding's temperature. The Prius windings were fully tested at 150A, with brief tests (to not overheat the stator) all the way up to 300A. At 150A, the Prius produced 150 Nm of torque. To match the rated 207 Nm of torque, the full 300A would be required. Coolant temperature is an important part of these tests, and the coolant input temperature was kept to 25C for the locked rotor tests and 0C for the efficiency tests. Obviously we won't be able to keep the coolant temperature anywhere near 25C on a hot Norcal day. I'll be happy if I can keep the coolant at about 50C.

Since Toyota doesn't publish how much current is required to produce the rated torque, I used the MGR's rated maximum torque of 130Nm and compared ORNL's tests of the Prius, Camry, and Lexus. At 125Nm Torque, the Prius requires 125A, while the Lexus requires 175A. The Camry is in the middle. Without having anything better to use, I chose an average of 150A, hoping the MGR is somewhere in that range.

Another set of tests were done for the "continuous" operation. Note for a car, "continuous" operation is MUCH shorter than an industrial motor would require. The Prius was tested at 50kW and the 14 temperature sensors were monitored. An upper limit of 150C was used for the tests. At 5000 RPM using 50C coolant, the motor was run for about 4min 30sec before one of the stator's temperature sensors exceeded 150C. Meanwhile, the coolant exit temperature increased to 75C. So, 50kW = 67hp. At 5000 rpm, the torque is 70ft-lb, or 95 Nm. For the Prius locked rotor test, this requires about 100A.

The last relevant issue is - how much current can you shove through a copper wire? This is commonly referred to as "current density" and detailed in the paper at the top of this post. The wires used in the MGR and the Prius are 0.032" in diameter. The cross-sectional area is 0.000804 in^2. The total wire area per phase leg is 12*0.000804in^2 = 0.00965in^2.

According to this paper, a water cooled motor (industrial?) can run steady state with a winding current density of 12,000 A/in^2. Locked rotor tests can go up to 25,000 A/in^2. So, 12,000A/in^2 * 0.00965 in^2 = 115A. Pretty modest, and corresponds with ORNL's continuous operation test at 50kW. 25,000A/in^2 * 0.00965in^2 = 241 A. This is REALLY close to ORNL's 300A locked rotor test for the Prius. The paper showes the "darkened" windings that can result from this. Obviously, insulation rating and cooling play a large part in the winding limit.

It appears that for the MGR, current should be limited to 175A > 200A, just to give some headroom because we only have one thermocouple, and the coolant temperature could be hotter that that used by ORNL's tests. Based on this, a 25% or maybe 50% increase in current over that required to produce the 130Nm max torque spec. Increasing the maximum speed to 13000 rpm should be safe and allow those using smaller tires or trying for higher speeds. For example, it would allow a maximum speed of 145mph for a vehicle running 235/45R18 tires.

[freebeard]

We were making an automatic trans-axle for applications such as Bugs or ground up custom jobs like the Ariel Atom. There are a few kit makers that offer skeleton cars that you add the parts you want to them. Electric trans-axles would fit right in there.

That's very interesting. I like the Riley XR-3 and the Blackjack Zero. Would you have been using Subaru or Porsche/VW axle shafts?

Since the MGR rotor slides onto a splined shaft, could you stack rotors and stators together on a longer shaft in a custom case?

Another set of tests were done for the "continuous" operation. Note for a car, "continuous" operation is MUCH shorter than an industrial motor would require. The Prius was tested at 50kW and the 14 temperature sensors were monitored. An upper limit of 150C was used for the tests. At 5000 RPM using 50C coolant, the motor was run for about 4min 30sec before one of the stator's temperature sensors exceeded 150C. Meanwhile, the coolant exit temperature increased to 75C. So, 50kW = 67hp. At 5000 rpm, the torque is 70ft-lb, or 95 Nm. For the Prius locked rotor test, this requires about 100A.

4min 30sec doesn't seem very long for sustained high speed. I'm as much interested in creeping uphill at walking speed. Would high torque, low rpm operation result in massive heat gain in the controller?

[Cyruscosmo]

Originally Posted by e*clipse

Here's what I don't get: Why do you need to shift gears at all?

Seriously - the rated speed with this motor is 10,500 rpm. Along with the stock 6.86:1 gear ratio and average sized tires, my calcs (and others) indicate that this is good for 115 mph. Now, 50kW may not be enough for that speed, but this is a power issue, not a transmission issue.

This is why I'm going for a two motor system initially. If spec'd with the correct battery, the car can easily handle normal driving conditions. Accelleration is reasonable, at about 8 or 9 seconds 0-60.

Would this be improved with a transmission? Not according to Tesla, who built the first Roadsters with 2 speed transmissions. Because of reliablity issues, they simplified to a single speed gearbox and re-tuning the motor.

I'm totally into the idea of a custom gearbox, similar to the MGR - just one that's a bit better suited for EV use.

I have had this discussion with Dave Cloud on a number of occasions. I respect his ideas and have been involved in the building of a couple of his cars. If you do a google search for his name you will find a long string of EV activities in connection with electric cars. Not the gospel singer Dave Cloud but the other one with the wild looking hair. That is my next-door neighbor...

He asked me the same question. Why a transmission?

In the case of "go faster, faster" it is a common practice to use stacked or coupled motors. Ask John Wayland a.k.a. plasma boy or the builder of the white zombie. Massive amps more power bigger cables more torque get off the line in a flash and on down the track. In his case he did use gears... kinda. Series and parallel wiring of the Siamese 9's through contactors provides a lot of torque to get off the line and then a lot of top end for speed. Then he switched to the zilla controller with 2000 amps capability.

Why 2000 amps? Why not 250 and a first gear in a transmission? There would be less copper to lug around and a lot smaller controller. Longer battery life? I am not sure but everything I have learned from Dave the past 6 or so years kinda indicates that a transmission instead of a huge motor, controller and a sheep load of amps would be a good thing.

I cannot even count the times someone has told me "they only drive around in one gear". And then explain that when they go up a hill or get on the freeway and need a bit more pep they do what? Pour on the amps? No. Add more motor? No. They shift to a lower gear to keep the amps from climbing to high. Hmm. They use "only" one gear huh?

In most of the applications I have seen where the vehicle has the get up and go of an ICE or better there is a large motor or two with a sheep load of cables the size of my thumb and a controller that could be used as a power source for an arc furnace. Why not use a smaller motor and multiply the torque with two gear ranges?

Yes Tesla tried some two-speed gear thing but in my experience with transmissions he did not try very hard. Helicopters have been running gear boxes for years with gas turbine engines that turn at 200,000 RPM's. As far as reliability goes there are two speed gearboxes out there that are older than both of use combined that still work fine. I can walk in to my local transmission shop and walk out with a two speed tranny that will handle 1000HP @ around 450 foot pounds of torque easy. I am not going to pretend to know why Tesla went the way they did but history would indicate that it had little to do with unreliable gears.

But I can only go on what I know and I know you can get more torque out of an electric motor with gears, you do loose the top end but where in average daily driving traffic are you going to need top end? Yes you could go with a bigger motor... or two or four but I think that is a bit more complication than the average Joe wants to mess with for a simple conversion.

Less amps, smaller cables, smaller controller, less strain on the traction battery set all done with two planetary gear sets, two clutches and two bands in a transmission that has proven it's reliability for over twenty years.

I won't know for sure until I try.

Cyruscosmo

[Cyruscosmo]

That's very interesting. I like the Riley XR-3 and the Blackjack Zero. Would you have been using Subaru or Porsche/VW axle shafts?

Since the MGR rotor slides onto a splined shaft, could you stack rotors and stators together on a longer shaft in a custom case?

We were going to keep "special parts" to a minimum. Since the final drive was from the Subaru the inner Subaru stubs were to be included in the kit. Any axle shop could fab a set of axles to match the customers outer CV application.

Yes you could stack them but then you will need two or more controllers and more battery and more copper and... more complexity. More complexity equals more problems to solve and more that can go wrong. Murphy loves complex problems.

4min 30sec doesn't seem very long for sustained high speed. I'm as much interested in creeping uphill at walking speed. Would high torque, low rpm operation result in massive heat gain in the controller?

If you had a couple lower gears you could switch to, the motor could stay at the same RPM/Voltage and trade the speed for torque. You just go slower...

Now if you upped the amps to make the motor develop more torque then yes the damn thing would get hotter faster. That is one reason I tend towards a couple extra gear ranges to use in case. I don't want the car to have a higher top end. I want it to have better drive-ability in the situations you would find in daily traffic. Creeping up hills in the Seattle area is a daily event driving to work.

Cyruscosmo

[e*clipse]

I'll just start by saying electric motors are not generic things.

For example, the 9" ADC motors used in the White Zombie are rated at 28hp each. That's roughly HALF of the power in the MGR. Siamezed, they will put out 56 hp.

If you look at the data from an ADC motor, you'll see two important things:
1) The whole power chart runs between 2500 rpm and 6500 rpm.
2) The torque speed chart totally disagrees with the specs, which claim stall torque numbers of 1000ft-lb using 144V. I'm going to assume below 2500 RPM is the "constant torque" region of performance, and this motor therefore puts out about 100ft-lb of torque from 0 rpm to 2500 rpm.

How does this compare to the MGR?
a) The MGR is rated to 10,500 rpm, and can probably run to 13,000 rpm - twice that of the ADC 9" motor.
b) The MGR's motor puts out a similar amount torque: 96 ft-lbs to 610 rpm and about 80 ft-lbs to 4500 rpm.

If you had a gearbox like the MGR ( 6.86:1 gear ratio ) and used the ADC 9" motor, the constant torque range would end at 30mph and the motor's max speed would limit the car to about 70mph.

This doesn't sound too bad until you look at the power curve, which indicates it will only be putting out 10 ft-lbs of torque at 6000 rpm. That's only 12hp. Siamezing the motors will only double your power - you still need a transmission to use the motor's capability. The reason the White Zombie performs so well is the motors are pushed WAY beyond their specs - and are only expected to do this for 10 to 15 seconds. He's pushing something like 355 volts, where all numbers for ADC 9" motors end at 144V. He's also pushing something like 2000A, while the ADC chart ends at 450A, but also shows a stall torque of 1000 ft-lbs using 3000A. None of this agrees with itself. However, pushing something like 10X the rated current through a motor might be just fine if drag racing is your thing. In this case, 2000A * 355V = 710kW - That's 952 HP!! No wonder he's so fast.

Compare that to the MGR, which puts out full torque until about 5000 rpm and a top speed of 13000 rpm. This means that through the normal driving speed range (up to about 60mph) you've got full torque. The full capability of the motor is available. If you really want a speeding ticket, you can push the motor to it's rpm limit at 140mph.

So, you're right - if you assume all electric motors perform like a big DC motor. But, they don't - that's why I'm using the MGR.

Regarding the ORNL "continuous" test - 50kW is near full power for that motor. How long could you keep the pedal mashed to the floor with an IC engine? Not very long, in my experience. You'd slow down to save your equipment. The same test performed by ORNL using 25kW and 25C coolent showed much longer run time - something like 35 minutes.

-e*clipse

[freebeard]

Before the horsepower increases began the VW Beetle was famous for having a top speed and cruising speed that were same.

Cyruscosmo -- I settle for 20" tires for the [paved or unpaved] hills and then swap to 28-32" tires for the Salt Flats. Would that count as two speeds?

[Cyruscosmo]

Originally Posted by e*clipse

I'll just start by saying electric motors are not generic things.

For example, the 9" ADC motors used in the White Zombie are rated at 28hp each. That's roughly HALF of the power in the MGR. Siamezed, they will put out 56 hp.

If you look at the data from an ADC motor, you'll see two important things:
1) The whole power chart runs between 2500 rpm and 6500 rpm.
2) The torque speed chart totally disagrees with the specs, which claim stall torque numbers of 1000ft-lb using 144V. I'm going to assume below 2500 RPM is the "constant torque" region of performance, and this motor therefore puts out about 100ft-lb of torque from 0 rpm to 2500 rpm.

How does this compare to the MGR?
a) The MGR is rated to 10,500 rpm, and can probably run to 13,000 rpm - twice that of the ADC 9" motor.
b) The MGR's motor puts out a similar amount torque: 96 ft-lbs to 610 rpm and about 80 ft-lbs to 4500 rpm.

If you had a gearbox like the MGR ( 6.86:1 gear ratio ) and used the ADC 9" motor, the constant torque range would end at 30mph and the motor's max speed would limit the car to about 70mph.

This doesn't sound too bad until you look at the power curve, which indicates it will only be putting out 10 ft-lbs of torque at 6000 rpm. That's only 12hp. Siamezing the motors will only double your power - you still need a transmission to use the motor's capability. The reason the White Zombie performs so well is the motors are pushed WAY beyond their specs - and are only expected to do this for 10 to 15 seconds. He's pushing something like 355 volts, where all numbers for ADC 9" motors end at 144V. He's also pushing something like 2000A, while the ADC chart ends at 450A, but also shows a stall torque of 1000 ft-lbs using 3000A. None of this agrees with itself. However, pushing something like 10X the rated current through a motor might be just fine if drag racing is your thing. In this case, 2000A * 355V = 710kW - That's 952 HP!! No wonder he's so fast.

Compare that to the MGR, which puts out full torque until about 5000 rpm and a top speed of 13000 rpm. This means that through the normal driving speed range (up to about 60mph) you've got full torque. The full capability of the motor is available. If you really want a speeding ticket, you can push the motor to it's rpm limit at 140mph.

So, you're right - if you assume all electric motors perform like a big DC motor. But, they don't - that's why I'm using the MGR.

Regarding the ORNL "continuous" test - 50kW is near full power for that motor. How long could you keep the pedal mashed to the floor with an IC engine? Not very long, in my experience. You'd slow down to save your equipment. The same test performed by ORNL using 25kW and 25C coolent showed much longer run time - something like 35 minutes.

-e*clipse

D Damn E*clips! I feels like I been schooled!

But that is a good thing, as I said I don't know electric motors the way I know ICE's.

Ok so I understand a few more things now. Why the little high revving AC motors use a lot of reduction gears like little gas turbines and why the big DC's don't. I had not thought about this until I read your post but when we started brainstorming the transmissions the only motors we had in mind were the big DC's.

My primary concern was reducing the wire sizes and amps needed to get a vehicle going in a timely manner without resorting to drastic measures like 2000amp controllers, huge cables, more batteries or stacking two 11 inch motors. Those things are not light! So the thought was a 9inch with a couple gears to help it along a bit.

I have a couple 9 inch motors here and a few boxes of C4 parts all I need is a case for those parts and I can give it a go. That will come next summer when I finish the forge and start making ingots.

So I imagine you know what the term "BLDC out-runner" is yes? I had this thought of building an 11 inch out-runner. My reasoning was to do away with the transmission all together only I was going the larger diameter low RPM more torque rout instead of the smaller diameter high RPM gear reduction rout.

What are your thoughts?

Cyruscosmo

[Cyruscosmo]

Originally Posted by freebeard

Before the horsepower increases began the VW Beetle was famous for having a top speed and cruising speed that were same.

Cyruscosmo -- I settle for 20" tires for the [paved or unpaved] hills and then swap to 28-32" tires for the Salt Flats. Would that count as two speeds?

LOL! Yes I think that would count for two distinct gear ranges. But I bet I can change "gears" faster than you can.

Cyruscosmo