[jk1981]

Sorry, I wasn't clear. I don't think mixing hub motors and big brakes in a car wheel is a good idea for the reasons you've also picked up on, inertia vibration and heat. I meant mount them inboard driving a shaft each.

Thinking more about it without some out of the ordinary sophistication (field control of some sort or electrically isolating the battery/controller from excessive BEMF at speed) you're not going to find a motor/controller pair capable of significant torque output and 150mph+ direct drive.

[dreamer]

Using a differential to get a 3.5x final drive ratio is not going to get very much torque on the ground, is it ? Torque from a series DC motor may be instantaneous, but it isn't huge. A multiplier of 3.5x isn't much compared to transaxles that yield 12x-15x in low gear. A 200hp vehicle should put something like 3000 lb-ft to the wheels after multiplication thru first a trans and then a diff, right ? The Warp9 might provide 250 lb-ft at 1000amps, so just 3.5x through a diff is pretty weak torque to the ground.

On the other hand, even such a low ratio is going to destroy the motor's bearings at speeds of 150+mph. Figure each wheel revolution will cover 6' of ground. At 150mph (150*5280/60/6) they will be turning at 2200rpm, and any motor attached to a 3.5 diff will be forced to turn at 7700rpm. A Netgain Warp9 may not survive 7700rpm. It is spec'ed at 5500rpm max which would barely get you to 100mph with a 3.5x diff.

Cars like the Tesla get away with only a single gear because they are running AC motors that can take 14000rpm, which means they can use a higher drive ratio than 3.5x.

Have you considered using a lightweight automatic transaxle from a Honda ? Get your 15x torque multiplier at launch and an overdrive final ratio under 3x that will keep rpms low enough the Netgain won't fly apart. Without ever shifting. Just put it in Drive, idle the Netgain via software in a Soliton Jr. just shy of stall converter speed. The efficiency loss in idling the automatic to keep the clutch packs ready shouldn't be a big deal in a hybrid where you aren't trying to eek out every last bit of range from the battery.

[Bowser330]

Originally Posted by dreamer

Using a differential to get a 3.5x final drive ratio is not going to get very much torque on the ground, is it ? Torque from a series DC motor may be instantaneous, but it isn't huge. A multiplier of 3.5x isn't much compared to transaxles that yield 12x-15x in low gear. A 200hp vehicle should put something like 3000 lb-ft to the wheels after multiplication thru first a trans and then a diff, right ? The Warp9 might provide 250 lb-ft at 1000amps, so just 3.5x through a diff is pretty weak torque to the ground.

On the other hand, even such a low ratio is going to destroy the motor's bearings at speeds of 150+mph. Figure each wheel revolution will cover 6' of ground. At 150mph (150*5280/60/6) they will be turning at 2200rpm, and any motor attached to a 3.5 diff will be forced to turn at 7700rpm. A Netgain Warp9 may not survive 7700rpm. It is spec'ed at 5500rpm max which would barely get you to 100mph with a 3.5x diff.

Cars like the Tesla get away with only a single gear because they are running AC motors that can take 14000rpm, which means they can use a higher drive ratio than 3.5x.

Have you considered using a lightweight automatic transaxle from a Honda ? Get your 15x torque multiplier at launch and an overdrive final ratio under 3x that will keep rpms low enough the Netgain won't fly apart. Without ever shifting. Just put it in Drive, idle the Netgain via software in a Soliton Jr. just shy of stall converter speed. The efficiency loss in idling the automatic to keep the clutch packs ready shouldn't be a big deal in a hybrid where you aren't trying to eek out every last bit of range from the battery.

+1, a lot of good points here.

There are trade offs to direct drive when you have a motor with lower redline.

I like the idea of hooking up an auto transaxle w/Idle but spend the extra 1000$ and get the Soliton-1, Impulse9 ~230ftlbs e-TQ * 85% eff = 196 m-tq, the honda transmission should be able to handle that.

[LSB]

Originally Posted by dreamer

Using a differential to get a 3.5x final drive ratio is not going to get very much torque on the ground, is it ? Torque from a series DC motor may be instantaneous, but it isn't huge. A multiplier of 3.5x isn't much compared to transaxles that yield 12x-15x in low gear. A 200hp vehicle should put something like 3000 lb-ft to the wheels after multiplication thru first a trans and then a diff, right ? The Warp9 might provide 250 lb-ft at 1000amps, so just 3.5x through a diff is pretty weak torque to the ground.

On the other hand, even such a low ratio is going to destroy the motor's bearings at speeds of 150+mph. Figure each wheel revolution will cover 6' of ground. At 150mph (150*5280/60/6) they will be turning at 2200rpm, and any motor attached to a 3.5 diff will be forced to turn at 7700rpm. A Netgain Warp9 may not survive 7700rpm. It is spec'ed at 5500rpm max which would barely get you to 100mph with a 3.5x diff.

Cars like the Tesla get away with only a single gear because they are running AC motors that can take 14000rpm, which means they can use a higher drive ratio than 3.5x.

Have you considered using a lightweight automatic transaxle from a Honda ? Get your 15x torque multiplier at launch and an overdrive final ratio under 3x that will keep rpms low enough the Netgain won't fly apart. Without ever shifting. Just put it in Drive, idle the Netgain via software in a Soliton Jr. just shy of stall converter speed. The efficiency loss in idling the automatic to keep the clutch packs ready shouldn't be a big deal in a hybrid where you aren't trying to eek out every last bit of range from the battery.

I agree, it would seem that at least with DC the only viable way is with a multi-geared arrangement, and at this stage I'd need more accurate measurements to workout which transaxle gearbox would fit/suit.

I feel that even using a more expensive 3-phase motor that the loss of torque at high speeds will effectively narrow the scope of the project. This car could be viable for racing if Regenerative Braking is exploited but when the car is at high speeds, the only torque generation will only come from the ICE which would hurt at higher speed tracks. The 3 phase motor may still be the best method though as it should require only 2 forward gears compared to DC which would require more ratios to deliver a sound torque curve.

Perhaps for drag racing the DC route is optimal vs 3 phase or bldc for racing.

I don't see any reason that a decent sized ac or dc motor wont fit with a transaxle as long as care is taken when changing the suspension geometry.

Batteries would have to be fit in the cockpit, as close to the front as possible. The car is released at sema this year which is late October I think, so I'll try and gather the specific details i need then and move from there. The poor old wreck will have to sit, gathering dust with my other unfinished projects..

[dreamer]

"Batteries would have to be fit in the cockpit, as close to the front as possible."

You could also think about a battery box that is under the cab of the vehicle. Using A123 pouch cells lying flat in 3P packs, laid out 9x7, you could create a 60"x60" box from aluminum diamond plat and extruded aluminum channels that was only 1" thick and bolted covering the bottom of the seating area. 63S3P would easily produce the 200hp you are looking for. That's a $7500 battery with 10kwh capacity. The advantage being low center of gravity and a smooth aero belly pan for the vehicle. The disadvantage being you have to drop the battery box to diagnose battery issues or possibly even to access the bottom of the engine depending on how far forward the engine sits.

[LSB]

Originally Posted by dreamer

"Batteries would have to be fit in the cockpit, as close to the front as possible."

You could also think about a battery box that is under the cab of the vehicle. Using A123 pouch cells lying flat in 3P packs, laid out 9x7, you could create a 60"x60" box from aluminum diamond plat and extruded aluminum channels that was only 1" thick and bolted covering the bottom of the seating area. 63S3P would easily produce the 200hp you are looking for. That's a $7500 battery with 10kwh capacity. The advantage being low center of gravity and a smooth aero belly pan for the vehicle. The disadvantage being you have to drop the battery box to diagnose battery issues or possibly even to access the bottom of the engine depending on how far forward the engine sits.

Thanks again for input, lots of food for thought. I recently saw the movie "Revenge of the Electric Car" Which shows exactly how they use their batteries, including the active and passive safety measures.

One of the passive attributes of their model S battery pack is that it sits under the floorpan of the car In a similar setup to that which you described. They use 18650 form factor which are of similar height to the A123's. The battery unit acts as part of the rigid structure which theoretically increases strength.

While the 63S3P is slightly more weighty than I had envisioned, when you estimate range under heavy load, any less than 20kw would limit its usefulness in racing as the charge that the kinetic charging or the ICE can produce will not be able match the output.

The effect that a battery unit like this will have on the desired weight distribution will be interesting. Using some very basic estimations I'll assume that the torque needed to surpasses tractable force of a 16 by 7" radial tyre to the front wheels (in a 1100kg vehicle) is around 2100nm. While this is easily achieveable with a 9" motor + 2.9:1 gear ratio and 3.5:1 diff ratio, we need to consider that this figure will be raised by the fact that the rear wheels are helping with forward thrust. The same obviously goes for the ICE powering the rear wheels. Due to this, because the ICE generates more torque in addition to the forward thrust of the vehicle sending many more forces to the back wheels, weight over the front would be well served to be kept as close to 50 50 as possible.

The advantage in this respect to using an electric motor at the front is that you can determine the exactly amount of torque to send to the wheels instead of having to mechanically input this using the clutch and accelerator like you would with the ICE. Therefore, in a drag race you just need to concentrate on launching at the top of the torque curve of the ICE.

I received an email from someone at Factory five about the specific dimensions of the chassis and body, but they are unable to produce it at this time as the car is still in development. However, they mentioned that the large area in the front where I had envisioned placing the electric engine has fiberglass channels running through it and up throught the bonnet (for downforce) which will mean bonnet modification will be needed.

[dreamer]

Originally Posted by LSB

Thanks again for input, lots of food for thought. I recently saw the movie "Revenge of the Electric Car" Which shows exactly how they use their batteries, including the active and passive safety measures.

One of the passive attributes of their model S battery pack is that it sits under the floorpan of the car In a similar setup to that which you described. They use 18650 form factor which are of similar height to the A123's. The battery unit acts as part of the rigid structure which theoretically increases strength.

The Tesla S can get away with 18650 cells arrayed vertically because they are actually sitting inside that stressed frame - so the 4" thickness is not hanging below the car and cutting into the ground clearance. I'd hate to scrape the battery box going over a speed bump ;-) You may be able to do that with the 818 since you are talking about a tubular frame based kit car. I generally think in terms of a bolt-on battery pack belly pan because it would work well in a conversion of a unibody car.

As far as the torque issues, you are talking about an unusual configuration and my suggestion for a transaxle didn't fully take into account.

You have torque from the ICE to the rear wheels, so ANY additional torque to the front wheels is better than none. By using a shorter 2.5x diff, you'd be adding 600 lb-ft to the 3000 lb-ft the ICE is putting to the rear wheels, which is only a 20% increase in torque but is consistent from 0 RPM -- and keeps the DC motor from exceeding its limits even at 150mph. And even though you can't get full torque to the ground, you are not relying entirely on the electric to launch, and at speed you do get all of the 200hp addition which is a 50% boost over your 400hp ICE.

For an all-electric vehicle, the diff alone would be sedate, I think, but for a hybrid where launching is not entirely dependent on the DC motor, maybe the diff vs. transaxle choice is not so clear. The diff would be less complex and more battery efficient, and as long as maximizing torque at launch isn't critical a lower ratio can make high speed survivable.

You could even go with a pair of these AC motors

http://www.evparts.com/products/stre...ors/mt5615.htm

belted together (there is a Fiero somewhere in the "garage" that's done this, although still using a transaxle). They have a 6500rpm redline, and produce 110 lb-ft each but only 67hp. You could use a 3.0 diff and not destroy them at 150mph. They'd get you no more torque, but they WOULD allow regen. They'd also cost $10K vs. $5K for DC.

[toddshotrods]

Originally Posted by dreamer

...for a hybrid where launching is not entirely dependent on the DC motor, maybe the diff vs. transaxle choice is not so clear. The diff would be less complex and more battery efficient, and as long as maximizing torque at launch isn't critical a lower ratio can make high speed survivable...

That's my route. Schism is using chain drives, for the aesthetic, but it is essentially a single ratio reduction; like you would have with a conventional diff. I'm gearing it for the top speed planned (which isn't going to be ridiculously high in an open-door runabout). I'm not concerned with launch because I'm using an 11" motor, which is way overkill for the size and weight of the vehicle. It should easily be capable of providing more torque than the front wheels can make use of, even with relatively high (low numerical) gearing. The point is just to add some forward momentum while the rear wheels search for traction (turbo ICE planned).

If you've ever driven a high horsepower FWD ICE car, you'll know that successfully applying massive amounts of power is a futile exercise, unless it's a purpose built Sport Compact drag car. I drove a friend's turbo Civic (approx 450hp) - any aggressive throttle pedal application below 55mph and the front tires spin wildly, sending the ICE into full boost, then bumping off the rev limiter. With a 16 x 7 inch radial tire, and an electric motor, you'll have the same experience, as the motor will be "on boost" from 0.

There's another component to this: your car might actually work better with highway gears anyway, as the electric motors will work harder and longer to overcome the nearer to stalled condition. With lower (higher numerical) gears, the torque would probably fall off sooner as the motor increased rapidly in RPMs. If you've ever watched any of White Zombie's runs, and remember the effect when he swapped in higher gears (I think first to something like 3.70, and then to 3.50?) it started pulling harder and harder.