Direct-to-diff conversion possibility?

[Isaac Zackary]

Originally Posted by Thalass

Hrm. Thanks for that! I do have a fairly steep hill to climb on my short commute. How do those numbers go with the 2:1 gearbox before the diff? Alternatively having the two motors should mean roughly twice the performance. (and twice the expense!)

Just off of the top on my head, you'd have twice the hill climbing power and acceleration at speeds below 25mph. That doubled torque would start to wean down after 25mph to about the same torque as before at around 40mph and continue down to about 60% of original (so about 2mph per second acceleration instead of 3) at around 50mph. It would be much less and limit at higher speeds and limit you from going much faster. But all in all, I think that if you were wanting a more practical vehicle the 2:1 ratio before the differential would be best. You'd be limited to a top speed around 55mph but at slower speeds it would feel more like a normal car.

[Isaac Zackary]

So optimal would probably something less than 2:1. Maybe 1.75:1. Or 2:1 and bigger tires.

[Thalass]

Hrm. The acceleration numbers for the 2:1 setup are slower than the standard, but not that much slower. (as per this: Subaru SVX (1995) - acceleration from 0 to 100 km/h ) The car would only be driving in town so 100km/h is not really a requirement, it'd just be embarrassing to not be able to go highway speeds hah. I'll have to look into more powerful motors. I want to go AC, for the regen, and want to keep stock-like performance. With the budget tradeoff being range.

Thanks for your help! Much appreciated.

[Isaac Zackary]

Yes. Acceleration and hill climbing would be worse than with the original engine. I think it would still do 100km/h though. But you'd get better overall acceleration and performance with a 2:1 gear reduction than without it.

If you could put on two motors (one front and one rear) you could do quite nicely. Especially with about a 7:1 total gear reduction. The only problem is that the gear reduction boxes I've seen are very expensive. I wonder If you could get some sort of a differential with 7:1 gears. Then get two of them and put two motors in.

[freebeard]

All IMHO of course, but...

The size of the motor isn't the only consideration. Using what I learned about a single-speed 10Krpm motor as an example; the stress on the system at low speeds is in the power circuits. It must deliver 1+ Coulombs at times. This means cooling on the inverter as well as (maybe more than) the motor and big, fat cables.

On the low end of rpm you are stressing drivetrain components that are used to forces applied in milliseconds being stressed in microseconds. Like clutches. On the high end top speed is limited by the back EMF. The FOC software needs to be tuned.

[Thalass]

Hrm. AC is much more complicated than DC. EV West's graphs for their dual AC-34 motors show a nice sounding amount of power and torque. Certainly makes two (not joined) motors look like a good idea, but as you say the diff ratio isn't really high enough. If max continuous rpm is matched to top speed (say 70mph/112km/h, at 5000rmp, I get a 5.28:1 ratio diff. This will mean I get a decent speed range, and ~ 633 foot-pounds of torque at the start(?) per AC-50 motor. So 1266ft-lbs for a two motor setup.

I dunno. I picked the AC-50 because it seemed good. I'm open to other motors, of course. And I'd much rather use Paul's motor controller than the Curtis one that EV West would bundle with the motor. But that's also just a personal preference. Those controllers are $1900 each on their own O_o

This is an expensive hobby. :P

[Isaac Zackary]

Originally Posted by Thalass

This is an expensive hobby. :P

That's why I've changed my mind about building a car and decided a used Nissan Leaf was a better choice for me. I've seen perfectly fine Leafs for $7,000USD. And I've heard that if you look around enough, there are some used car dealers that are trying to get rid of them for as little as $5,000. To that off with living in Colorado, as in my situation, and I can get a 24% tax rebate putting a used 2011 or 2012 Leaf at less than $4,000. I'm actually looking at a low mileage 2013 for around $8,000 right now since the 2013's have a more efficient heater.

[Thalass]

Yeah I've been tempted, but I've also been talking about doing this for nearly eight years now. I don't think I'd be satisfied with an OEM car (other than a tesla, but they're out of my budget! haha). Also we bought my wife a new car at the beginning of last year. So I figure that if it's spread over a few years I can push my budget up towards 20k without feeling too guilty. As long as the end result is fun.

[thingstodo]

Originally Posted by Thalass

This is an expensive hobby. :P

Yes ... yes it is ...

[bryn]

there was a post about toyota suv hybrid diff/motor combo. for the rear wheels to make it 4wd i think it was about 100 pounds motor/diff with good power, if you just had one front and one rear. you would just have to make custom half shafts, and find a way to control
them