RX400H transaxle

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Post by PlanB » Sun, 12 Aug 2012, 16:32

Tritium's 6000RPM Eurodrive mounted on a 5.1:1 MX5 differential to scale in a SmartRoadster, the SmartSew or SewSmart perhaps? I'd have to cut a hole in the boot lid for the motor fan exhaust with the vertical mount but the horizontal config might shoe horn in? Comments from the mechanically savy?
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Post by weber » Sun, 12 Aug 2012, 18:06

PlanB wrote: Tritium's 6000RPM Eurodrive mounted on a 5.1:1 MX5 differential to scale in a SmartRoadster, the SmartSew or SewSmart perhaps? I'd have to cut a hole in the boot lid for the motor fan exhaust with the vertical mount but the horizontal config might shoe horn in? Comments from the mechanically savy?

I don't believe there is any 5.1 MX5 dif. The biggest number I know of is 4.3. I don't know what the underside of a Smart Roadster looks like, but I looked up some info and it appears to have a transversely mounted rear engine with rear wheel drive. It looks like the engine and transaxle are above and between the wheels. There is no reason why there would be any kind of compatibility of mounting or coupling between an MX-5 diff and a Smart Roadster. Your 132 frame motors are not to scale. They are shown too small. You have motor diameter being 1/3 of tyre diameter. That would make the tyres 132*2*3 = 792 mm in diameter! They are really only 586 mm. The motor could not end up as close to the axle as you have shown because you need a coupling between the motor shaft and diff shaft to allow for small misalignments in both offset and angle, otherwise the bearings in either the motor or the diff wont last very long.

In short, you can do just about anything given enough time and money, but in my opinion this would require way too much of both. And definitely not something for a first time converter.

But mounting the motor transversely and connecting it to the existing transaxle might be feasible. You'd need to find someone who would let you crawl over and under theirs and take lots of photos and measurements to determine if the SEW motor could fit where the engine is now.
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Post by PlanB » Mon, 13 Aug 2012, 19:24

You can buy 5.1:1 so called 'racing' diffs on a couple of the MX5 enthusiasts forums Dave.
The Eurodrive is 250mm across the faceplate & 2.3 of them fit across the tire diameter so that's about right I think. Mindful of CAD pitfalls I actually double checked the scaling by how many of the 0.517m long motors fitted along the car's 3.427m length.
Look I think you're right anyway a dumb idea. Had a look at a 2006 Roadster this morning, big gaps between the doors & the body work, pretty ordinary for a vehicle that cost $35k new just 6 years ago.

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Post by weber » Mon, 13 Aug 2012, 20:17

My apologies re the scaling. It is the motor body diameter (including cooling fins) that I estimated as going into the wheel diameter 3 times. I mistakenly assumed that was the same as our ABB motor which is 264 mm, the largest a 132 frame motor can be. Our flange is 300 mm dia.
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Post by PlanB » Mon, 13 Aug 2012, 22:02

No worries. I'm off to beautiful downtown Newcastle this Saturday to ogle Bret's delorean & that super expensive yellow thing at the Hunter EV festival. How's progress with your creation? You guys must be getting close?

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Post by PlanB » Wed, 15 Aug 2012, 16:32

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Post by weber » Wed, 15 Aug 2012, 17:07

What's wrong with having a tailshaft in between the motor and the diff?
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Post by PlanB » Wed, 15 Aug 2012, 17:59

It's messy with having to have that gearbox nose in place to make it work & it puts the motor in the engine bay. I just don't think I could pull it off.
And I can't find a rear wheel drive donor that will fit Tritium's Sew direct to the diff. Which brings me back to the EVOs.
The 140-3 up to 600Nm launch torque (18s) 400Nm peak torque (60s), 1.36Nm/A 2850 rpm @ 320v DC & 4000 rpm at 450v DC, 396mm dia. Or the 130-4 350Nm for 20s & 250Nm for 60s, 1.07 Nm/A 4400 rpm @ 360v DC, 300mm dia.

The wavesculptor is limited to 300A motor current & 450v packs sag to 380v on load. I interpolate the 140-3 to 3381 RPM at 380v, & the 130-4 to 3483 rpm @ 380v. The smallest MX5 diff ratio is 3.63:1 for the NB8B models & 16" wheels have a tire circumference of 1.99m, so 110km/h road speed equates to 921 RPM. So both motors qualify speed wise (931 RPM for the 140-3 & 960 rpm for the 130-3 post diff). The 140-3 gives 408Nm from 300A, 192Nm short of it's launch max but OK for peak. The 130-4 yields 321Nm from 300A, 50Nm short of it's launch max. I'm thinking the 130-4 is probably easier to fit mechanically, it would give 321 x 3.63 = 1157nm at the wheels but the 140-3s 1481Nm would be nice if it would fit forward of the diff.

Could you please check my calcs Dave & comment on the likelyhood of getting the 140-3 directly onto the diff.
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Post by coulomb » Wed, 15 Aug 2012, 19:06

PlanB wrote: The smallest MX5 diff ratio is 3.63:1 for the NB8B models & 16" wheels have a tire circumference of 1.99m, so 110km/h road speed equates to 921 RPM.

3.63:1 sounds very low for a direct drive setup. 1157 Nm is just OK at the wheels, but you could use plenty more for better acceleration, and 921 RPM is surely nowhere near the capability of the EVO motors. [ Edit: Wrong! The 921 RPM is at the wheels, not motor (thanks for the correction below, Weber). ]

So you have a vehicle that is capable of getting to hundreds of kilometers per hour. Eventually. My suggestion is that 3.63:1 is way too tall. Or am I missing something?

[ Edit: yes, I was missing that the 921 RPM was at the wheels. Sigh. ]
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Post by weber » Wed, 15 Aug 2012, 20:24

PlanB wrote: It's messy with having to have that gearbox nose in place to make it work
That depends what you mean by "messy". It is certainly _less_work_ to do it with tailshaft and gearbox "nose". Doing it near the diff, on a car with "FR" or "FMR" layout, means that you have to devise motor mounts on a part of the car that was not designed for it, instead of just using the existing engine mounts. You have to add a flexible shaft-coupling instead of using the tailshaft with its two Cardan joints that you get for free. And because the play allowed by compact flexible couplings is so much less than that allowed by a tailshaft you need to devise a means of rigidly coupling the body of the motor to the body of the diff.

Basically, what you see between the two motors on Ian's RX-7, you'd need to do between the motor and diff, and then devise rubber hanging-mounts for the motor similar to those on the diff. Plus, the diff body is often the lowest point on the car, so if the motor has a larger diameter than the diff, you're in trouble.

But I've often thought it would look cool to have the induction motor projecting into the cabin, between the seats. Image
& it puts the motor in the engine bay.
No it doesn't. It puts the motor where the gearbox and bell-housing used to be.
And I can't find a rear wheel drive donor that will fit Tritium's Sew direct to the diff. Which brings me back to the EVOs.
... 396mm dia.
... 300mm dia
...
Could you please check my calcs Dave & comment on the likelyhood of getting the 140-3 directly onto the diff.

Sorry I haven't checked the calcs, but the larger diameter of the EVO just makes things worse re ground clearance. To do what you want to do, with either the SEW or the EVO, you need a car with "RR" or "RMR" layout, but not "RMR-T".

[Edit: Underlined the links because it's easy to miss the dark-blue that indicates they are links, when they are only 2 or 3 characters long]
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Post by weber » Wed, 15 Aug 2012, 21:23

But RR or RMR does mean you will probably have to deal with a transaxle rather than separate gearbox and diff. Not sure why that's a problem though.

How about one of these? A GT-40 replica. They are RMR.

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Post by weber » Wed, 15 Aug 2012, 21:45

PlanB wrote:The smallest MX5 diff ratio is 3.63:1 for the NB8B models & 16" wheels have a tire circumference of 1.99m, so 110km/h road speed equates to 921 RPM.

Coulomb prompted me to check these calcs at least. That's 921 rpm at the wheels, so it's 3350 rpm at the input to the diff.
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Post by PlanB » Wed, 15 Aug 2012, 23:11

Replica looks good. So I should be looking at something like a Toyota MR2 weber? I've checked them out, the diff seems to be tacked onto to the side of the main gearbox via an internal gear, so it's hard to separate the 2 functions. If I keep the gearbox then I've got the extra weight & the clutch. Sigh, I don't see why Borg Warner can't put their 31-03 egeardrive gearbox out there.

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Post by weber » Thu, 16 Aug 2012, 00:22

PlanB wrote: Replica looks good. So I should be looking at something like a Toyota MR2 weber?
It's a thought. Oh wait ... It's transverse. RMR-T.
http://www.evalbum.com/3229
I've checked them out, the diff seems to be tacked onto to the side of the main gearbox via an internal gear, so it's hard to separate the 2 functions. If I keep the gearbox then I've got the extra weight & the clutch. Sigh, I don't see why Borg Warner can't put their 31-03 egeardrive gearbox out there.

http://www.drivelex.com/showthread.php/ ... on-diagram
Scroll down to see an exploded diagram. But I don't understand which bit is the diff or where the output happens.

But yeah, you're much more likely to be able to separate the gearbox from the diff with a longitudinal-engine RMR (or a longitudinal-engine RR like a DeLorean or a VW beetle).
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Post by weber » Thu, 16 Aug 2012, 00:45

Here a search idea for you. Search on "GT40 replica transaxle" without the quotes and you'll find lots of different cars that have longitudinal-engine RMR. Maybe one of those will be suitable to convert in the manner you want.
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Post by PlanB » Mon, 20 Aug 2012, 17:54

Anybody care to give me a reality check on the thinking below. I'm like a little wind up toy soldier, going in circles at the mo but I'll be right once I get pointed in the right direction.
1) Gearboxes. I can't seem to get away from them. Even Motor-to-diff on a rear wheel drive seems to need at least part of the gearbox. So why don't I just go front wheel drive? Lots more donors to choose from, just uncouple the ICE & put the motor onto the gearbox with an adapter plate like the DC guys do?
2) All up weight. It seems that the all up weight of the conversion has to be less than or equal to the max weight of the original car with full pax & fuel? Because I want at least 200km range (32kwh battery)I'm thinking a 4 seater 2 door, something like a '98 Celica? Big flat area at the rear under the lift back, even more if the rear seats removed. Room for a large flat (high cooling surface area) battery pack?

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Post by Johny » Mon, 20 Aug 2012, 18:47

Having done a rear wheel drive car with no gearbox it was pretty simple. The only reason I started with a rear wheel drive is because it was a classic and I wanted it back on the road.
Having said that, a front wheel drive with gearbox would probably be the same efficiency, or better - especially if you "played" around with the gearbox and removed gears you don't need - like 1st and third.

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Post by weber » Tue, 21 Aug 2012, 02:40

PlanB wrote: Anybody care to give me a reality check on the thinking below. I'm like a little wind up toy soldier, going in circles at the mo but I'll be right once I get pointed in the right direction.
1) Gearboxes. I can't seem to get away from them. Even Motor-to-diff on a rear wheel drive seems to need at least part of the gearbox. So why don't I just go front wheel drive? Lots more donors to choose from, just uncouple the ICE & put the motor onto the gearbox with an adapter plate like the DC guys do?
A perfectly sensible thing to do. However there may be less room for a long emotor in a transverse (east-west) orientation.
2) All up weight. It seems that the all up weight of the conversion has to be less than or equal to the max weight of the original car with full pax & fuel?
Not essential, but it sure makes life easier.
Because I want at least 200km range (32kwh battery)I'm thinking a 4 seater 2 door, something like a '98 Celica? Big flat area at the rear under the lift back, even more if the rear seats removed. Room for a large flat (high cooling surface area) battery pack?

All very sensible.
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Post by T2 » Wed, 29 Aug 2012, 09:37

So I've been pecking around Evo-electrics website. Heck, they don't give you a lot of info to go on.
Unless you decide to use 600Vdc there is no torque graph to give guidance on motor performance, that's if you had decided to use a less stratospheric voltage like 320Vdc and would be curious as to how peak torque would pan out past 2150rpm for the most recommended motor, the AFM-140-4, for instance.

Knowing that most of their clients would be using somewhat less than that wouldn't you think they should at least publish the performance that is to be expected on 320Vdc ?
This would save speculation regarding the 60sec and 18 sec torque ratings and the expected power ratings at top speed.
Anyway that is my rant on EVO.

For the AFM-140 motor series I was able to get good correlation between quoted torque figures and the torque constant, Kt. However although they mention nominal torque and nominal power they leave you to detemine what nominal speed is.

Doing some calculations for 320Vdc it turns out that at the base speed of 2150rpm you can't get the advertised power of 75Kw but only 49.5Kw. This is with the -4 motor.
Further calculations with the -3 motor with the 2850rpm base speed gives the much better result of 65.6Kw as I would have expected. But then again it's still shy of the 75Kw of course.

I then investigated the smaller AF-130-4 and -3 series.These motors weigh in at 30Kg which is 10kg less than the AFM-140 series. They allegedly pump out 64Kw, with base speeds of 2850 and 3800 for the -4 and -3 variants respectively. The -3 piqued my interest as it is close to the 5000rpm limit.
I noticed that even though this range of motors is specified as having a top speed of 8000rpm, the base speed chart has footnotes discouraging its use above 5000rpm, strange that.

Again I proceeded to investigate its usage with 320Vdc since the torque graph shows only for 600Vdc. Although torque for this series is 145N-m rather than the 220N-m of the AFM-140 series motors, they seem able to throw out a healthy 43.3Kw and 57.7Kw respectively. The torque drop off from 3800 to 5000rpm would probably be less significant for the AF-130-3 than all the other choices considered so far. Peak torque of 250N-m should be manageable for 60secs.

Then I came across an anomaly. Using the torque constant Kt of 0.8 A/N-m the -3 required 181 amps which with root3 times 232Vac came to 72.7Kw not 57.7Kw as expected. However resetting Kt = 1.01 N-m/Amp and everything balances out. In which case only 143 amps should be needed to produce the rated 145N-m instead of the 181 amps mentioned previously.
Similarly the AF-130-4 should have a Kt = 1.35 N-m/Amp not 1.07 N-m/Amp by my reckoning.

Also if AFM-140-3 has the same base speed as AF-130-4 of 2850rpm then how come their Ke's are different when working off the same 320Vdc supply ? They are 0.81Vs/rad and 0.86Vs/rad resp. I would put all this down to documentation errors which don't detract from the operation of the motor or drive. As a general rule shouldn't motors with the same Ke have the same Kt also however they are built ? I think they should.

How come base speeds are quoted for no load current ? These are synchronous machines fitted with feedback tachs, they should therefore hold the same rpm irrespective of loading, no ?

Why does the AFM-140-4 motor suffer a torque drop from 220N-m to 180N-m on its way to base speed at 4000rpm ?
The suggestion has been made that since this is a continuous power curve, current may have had to be gradually lowered so that the increasing iron losses with speed could be offset by lower copper losses.

However for the Peak Torque plot there is not even an ounce of torque drop off for that curve until the exact moment it passes above the 4000rpm base speed ? Makes you wonder if they did that test.    

Plan B wrote :
The 140-3 up to 600Nm launch torque (18s) 400Nm peak torque (60s), 1.36Nm/A 2850 rpm @ 320v DC & 4000 rpm at 450v DC, 396mm dia.
Or the 130-4 350Nm for 20s & 250Nm for 60s, 1.07 Nm/A 4400 rpm @ 360v DC, 300mm dia.

The wavesculptor is limited to 300A motor current & 450v packs sag to 380v on load.
I interpolate the 140-3 to 3381 RPM at 380v, & the 130-4 to 3483 rpm @ 380v.
The smallest MX5 diff ratio is 3.63:1 for the NB8B models & 16" wheels have a tire circumference of 1.99m, so 110km/h road speed equates to 921 RPM.
So both motors qualify speed wise (931 RPM for the 140-3 & 960 rpm for the 130-3 post diff).
The 140-3 gives 408Nm from 300A, 192Nm short of it's launch max but OK for peak. The 130-4 yields 321Nm from 300A, 50Nm short of it's launch max. I'm thinking the 130-4 is probably easier to fit mechanically, it would give 321 x 3.63 = 1157nm at the wheels but the 140-3s 1481Nm would be nice if it would fit forward of the diff.


-Plan B You state The 130-4 yields 321Nm from 300A i.e using EVO's 1.07 N-m/Amp figure.
That would be great except for one thing. I think that EVO's 1.07 figure is wrong, it's the anomaly with the AF-130 series that I was referring to above. For the AF 130-4 motor, in particular, I believe the figure should in fact be 1.35N-m/Amp. And while on the subject that for the AF 130-3 should be 1.01N-m/Amp.

To repeat myself, if two machines have the same base speed working from the same Vbus then they should generate equal torques with the same current providing the wiring in each case can handle that current. On 320vdc (232Vac) both AF 130-4 and AFM 140-3 have a 2850 RPM base speed therefore their N-m per amp should be the same and equal to 1.35N-m/A.

That being so, then with 300A both should deliver that 408N-m figure. However, the 130-4 will now exceed its launch max so perhaps 300Amps with this motor may not be wise.

Not that my opinion is wanted but I spent some time rehashing an old post so here comes the commercial.

I don't think that replacing an ICE with an equivalent electric motor is a particularly good idea.

I think it's time to slow down a minute and look at the end game. Consider that even if there existed an ICE that could somehow miraculously deliver its full torque at 0 rpm do you think that they would ever try to drive it straight into the differential, so why would you ? Cos' that's what it seems you are trying to accomplish here. A hypothetical ICE that could be directly connected to the wheels interposed with only a 3.63:1 reducer would undoubtedly move the vehicle but it would drive like a slug. Both you and I know it, so why ....?

edit: correct codes to make italics work for PlanB's comments.
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Post by PlanB » Wed, 29 Aug 2012, 15:47

    I don't know T2, I've been circling EVs for a couple of years & getting nowhere. If I keep the gearbox & replace the ICE with an electric motor of nearly the same weight then there is a problem with the 300kg of batteries I need for 200km range.
    
    Other folks seem to make a choice, Sutho with his 40kg AFM-140 in the DeLorean, Weber with his 90kg ABB in the MX5 & things just work. I can't even get the numbers to make sense let alone build one.
    
    Somedays I think I should just go down to my siblings garage & give him a hand with his next V8 muscle car rebuild, known quantities, predictable outcomes, it would make a nice change.

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