# HPG AC motors direct drive?



## JRP3 (Mar 7, 2008)

Sounds like a bad idea.


----------



## frodus (Apr 12, 2008)

directly, not a great idea

Through a single speed gearbox? maybe, but you need a way to disconnect for high speed driving.


----------



## sholland (Jan 16, 2012)

So, you think reduction would be necessary...

Would I basically calculate the necessary ratio based on max motor rpm and max vehicle speed? Say 100mph, 23.1" tire diameter, 6000 motor rpm using this calculator comes up with ~4.11:1.

What is this motor like when not being run, e.g. 0% throttle? What kind of static drag would it present?


----------



## frodus (Apr 12, 2008)

reduction would be neccessarily IMHO

That's how I'd calculate the ratio, but I'd try to stay in the high torque area of the motor curve. At 6000RPM the torque is lower than it would be if you kept it around 3000RPM. Try to keep max HP RPM where you want to peak.

The motor itself has an inertial load, you could measure that weighing the rotor. The big thing here, is if you want regenerative braking, it would depend on what the controller is set to. if you set to 100% regen, it would really load down the vehicle, but it would charge the batteries.


----------



## sholland (Jan 16, 2012)

I only used 6000rpm as a 'max' speed that I anticipate the car will ever see. I don't normally drive at 100mph , and honestly, I don't expect that the electric motor alone would power the car when going that fast. Really, electric only at lower speeds would be great, with the ICE coming in when higher speeds and/or acceleration would be necessary.

Hmm, so 4.11:1 reduction means I'll need a differential, therefore a single motor would be best...

Any suggestions on the most space efficient differential solution? Ideally a transverse mount would best for my application...


----------



## sholland (Jan 16, 2012)

Basically, one of these would work, though I'd prefer a transverse mount of some kind.


----------



## frodus (Apr 12, 2008)

is there even room under the car in the back for that? I mean, you'll have to move the gas tank I'm sure, as it'll get in the way.... civics are FWD, so they wouldn't have any accomodations for a rear diff, would it?


----------



## sholland (Jan 16, 2012)

frodus said:


> is there even room under the car in the back for that? I mean, you'll have to move the gas tank I'm sure, as it'll get in the way.... civics are FWD, so they wouldn't have any accomodations for a rear diff, would it?


I have found several 4wd Civic conversions out there, typically more for racing, so drive shafts and a diff. Usually, an entire CR-V drivetrain and rear subframe is swapped in. Guys have incorporated either a race fuel cell relocated somewhere else, or a hump-shaped tank from a 4wd Civic available in another country.

I am thinking if I can find a transverse mount of some kind, it would be possible to keep the fuel tank where it is.


----------



## sholland (Jan 16, 2012)

The Team Industries EV30 is almost right... Not quite strong enough.


----------



## sholland (Jan 16, 2012)

Another option... http://www.benevelli.it/products.html


----------



## JRP3 (Mar 7, 2008)

My 2500lb Fiero with an AC 31 motor has pretty weak starting torque taking off from a stop in 3rd gear, which is an overall ratio of 4.875, 4.10 would be worse. 2nd gear, 6.843 ratio, is very usable from 0-65mph with a 6500 RPM max, and that's what I use for 99% of my driving.


----------



## sholland (Jan 16, 2012)

Hmm, so the problem that really needs to be solved is the gear reduction...


----------



## frodus (Apr 12, 2008)

and a means to disconnect if you need to go high speed.

up to 8000rpm should be ok on an AC20, and 6000 on an AC35/AC50, but over that, it could damage the motor.


----------



## JRP3 (Mar 7, 2008)

Actually I think HPEVs said their motors are good to 10K, there is just no power up there. I've pushed mine to 7500 with no issues, I think Tomofreno has done the same. 7500 made my first gear usable to almost 45mph, but didn't have enough power to raise my top speed in second gear much, I think I could hit 70 at 7500 on the flat, with a tail wind.


----------



## Bowser330 (Jun 15, 2008)

love this idea...thanks for starting a thread about it.

If it is possible for the AC50 to safely spin up to 8000rpm then a higher numerical ration would be a perfect...

the room/space is an issue on a FWD car design, the fuel cell relocation is a good idea.

how those are cool differentials, but no prices...I wonder if it would be cheaper to get the CRV parts and do it that way?

I would like to do the same thing with an AC-50, to a FWD car. I was told that the rpm of the electric motor would synchronize with the ICE wheels rpm, through the road. So as the ICE speed would increase so would the e-motors wheels and the corresponding voltage.

I was also thinking about an AC50(dual shaft) in the middle of a rwd car similar to how netgain used the EMIS. the AC-50 would be able to regen,and would use a lighter lithium pack, unfortunately the stock rear-end on my car is only 3.46 I think...so that would make for more midrange power as i understand it...


----------



## sholland (Jan 16, 2012)

I've been thinking about this for a long time... I may be a new poster to DIYElectric Car, but I've lurked for a long time. I design BMS systems in my day-time job, and I was originally thinking of converting my Civic to a full EV, but it just isn't practical for my needs. The car was used for autocross racing, and is pretty heavily modified (suspension, engine, transmission, etc.). I am now wanting to return it to full CA smog and daily driver status, and I am missing the boost the turbo once provided. My thought is that an electric motor on the rear wheels could be my new 'boost' as well as making it an efficient commuter too. Kinda the best of both worlds! 

The Honda CR-V rear diff may work, especially as it has an integrated multi-disc clutch, but it may not have the gear reduction that is necessary. Using it will of course mean relocating the fuel tank. 

Another option is to use a Toyota IFS (rear-facing) as higher ratios are readily available. Hopefully I could get away with keeping the fuel cell where it is, with the electric motor hanging out behind the rear axle line. There obviously isn't much room to hang out too far, so mounting the motor beside or above the diff would be necessary. I think something could be fab'ed up for that. The Toyota IFS would also give enough torque handling to allow for future upgrades to a full EV if wanted.

I'm still researching other possible differentials for use... The Ferrari FF PTU for the front wheels would be nice!


----------



## Bowser330 (Jun 15, 2008)

If you had a rear facing diff, could you cut away the space tire well to allow for room to mount the motor? 

Is it a requirement to mount the motor in a horizontal orientation? could the diff be tilted or turned and the motor be perpendicular to the shafts (vertical orientation)?


----------



## sholland (Jan 16, 2012)

Yes, that's the thought... There is some room to do rear-facing, either stacking the motor above the diff with a gear/chain drive or keeping the whole assembly as short as possible. Vertical might work too. The AC motors are pretty short.

A transverse input differential would be nice, like what's in golf carts, but they just can't support the continuous torque I would need.

Actually the clutches in the CR-V diff are starting to look really worth having. If only it could be rear facing too... Maybe it would support high-pinion mounting, e.g. upside-down. Not sure...


----------



## Bowser330 (Jun 15, 2008)

sholland said:


> Yes, that's the thought... There is some room to do rear-facing, either stacking the motor above the diff with a gear/chain drive or keeping the whole assembly as short as possible. Vertical might work too. The AC motors are pretty short.
> 
> A transverse input differential would be nice, like what's in golf carts, but they just can't support the continuous torque I would need.
> 
> Actually the clutches in the CR-V diff are starting to look really worth having. If only it could be rear facing too... Maybe it would support high-pinion mounting, e.g. upside-down. Not sure...


Sorry im just rambling here...trying to get all my ideas out of my head, haha.

- what about using a flatter motor, the Agni95 can peak 30hp and is a flat style axial flux type motor, it is a high rpm motor, so gearing is very necessary. http://www.electricmotorsport.com/store/ems_ev_parts_motors_agni_motors.php agni95 is ~24lbs

- what about using Direct Drive like you originally mentioned, using the motorcycle motors from http://www.ev-propulsion.com/motorcycle-hub-motors.html 30kw peak would be nice, i heard they are 60lbs though...

Check out what evpropulsion is working on: http://www.ev-propulsion.com/projects.html They took two of their direct drive motorcycle motors and installed them into a subframe setup that could be installed into a Miata. You can try to do something similar...maybe contact them for more details on that setup...


----------



## tomofreno (Mar 3, 2009)

JRP3 said:


> Actually I think HPEVs said their motors are good to 10K, there is just no power up there. I've pushed mine to 7500 with no issues, I think Tomofreno has done the same. 7500 made my first gear usable to almost 45mph, but didn't have enough power to raise my top speed in second gear much, I think I could hit 70 at 7500 on the flat, with a tail wind.


 Bill told me 8k max. I've had mine to 8.4k (280 Hz), but I've since set the max to 7.5k - more due to concern for the transmission.

The AC50 has a fair amount of power at 7k (compared to peak), but not much torque. Its mostly rpm, compared to below peak power where it is mostly torque, lower rpm.

It takes a bit less than 1100 ft-lb wheel torque to accelerate my 2260 lb car (edit: with flywheel and clutch) at 6 mph/sec. Acceleration, a = tractive effort/mass = F/m = T/mr, where T is wheel torque, r is dynamic wheel radius, so scales linearly with mass and wheel torque. Wheel torque = motor torque*g, where g is the overall gear ratio.


----------



## Bowser330 (Jun 15, 2008)

tomofreno said:


> Bill told me 8k max. I've had mine to 8.4k (280 Hz), but I've since set the max to 7.5k - more due to concern for the transmission.
> 
> The AC50 has a fair amount of power at 7k (compared to peak), but not much torque. Its mostly rpm, compared to below peak power where it is mostly torque, lower rpm.
> 
> It takes a bit less than 1100 ft-lb wheel torque to accelerate my 2260 lb car (edit: with flywheel and clutch) at 6 mph/sec. Acceleration, a = tractive effort/mass = F/m = T/mr, where T is wheel torque, r is dynamic wheel radius, so scales linearly with mass and wheel torque. Wheel torque = motor torque*g, where g is the overall gear ratio.


Would you mind completing the formula by using your car as the example?

Acceleration = wheel torque/(mass * radius)???


----------



## tomofreno (Mar 3, 2009)

Bowser330 said:


> Would you mind completing the formula by using your car as the example?
> 
> Acceleration = wheel torque/(mass * radius)???


Well, say you have 1000 ft-lb = 1356 N-m wheel torque, a 2060 lb or 1030kg vehicle, and dynamic tire radius of 10.37 inch or 0.26 m, then acceleration would be about 1356/(1030*0.26) = 5 m/sec squared, or 11 mph/sec ignoring drive train efficiency and inertia effects of rotating parts such as the flywheel. If these are included, 0.9 for efficiency and a 1.49 mass factor for inertial effects in 1st gear, then you get 11*0.9/1.49 = 6.75 mph/sec. Quite a difference isn't it. Edit: note that torque here is the net torque = difference in available wheel torque and required wheel torque (required to move the car at a given constant speed) which is increasing as the car accelerates.


----------



## sholland (Jan 16, 2012)

Let me try to apply my Civic's previous performance (with Turbo) to that equation, since what I'm trying replicate...

It had 230 ft-lbs at ~3500rpm, with 3.25:1 1st gear and 4.25:1 final drive. 23.1" (0.586m) tires, and ~2400 lbs. I guess wheel torque = 230 x 3.25 x 4.25 = 3177 ft-lbs = 4308 N-m. I'm guessing I'll add roughly 300 lbs to the car.

So 4308/(1350*0.293) = 10.89m/sec^2 or 24.36mph/sec (1 m/sec^2 = 2.23693629mph/sec)

Applying the various weighting factors you provided to get a more real world number... 24.36*0.9/1.49 = 14.71mph/sec

Yikes!!

Since I'm only trying to replace what is lost by removing the turbo (I'll still have the FWD ICE which is ~96ft-lb), I can expect 96*3.25*4.25 = 1326ft-lb or 1798N-m. Therefore 1798/(1350*0.293) = 4.54m/sec^2 or 10.17mph/sec.

The difference is what needs to come from the RWD electric motor... 14.71 - 10.17 = 4.54mph/sec and working backwards to get a real world 7.52mph/sec.

Does that all look right? My little car was pretty quick with that turbo in there... I also chose the peak torque and first gear, where there was often quite a bit of wheel spin. I really don't need to fully replicate that with my electric boost, but close would be nice, as I won't be spinning the front wheels nearly so much with good traction on the RWD propulsion.


----------



## tomofreno (Mar 3, 2009)

sholland said:


> Let me try to apply my Civic's previous performance (with Turbo) to that equation, since what I'm trying replicate...
> 
> It had 230 ft-lbs at ~3500rpm, with 3.25:1 1st gear and 4.25:1 final drive. 23.1" (0.586m) tires, and ~2400 lbs. I guess wheel torque = 230 x 3.25 x 4.25 = 3177 ft-lbs = 4308 N-m. I'm guessing I'll add roughly 300 lbs to the car.
> 
> ...


That is quite a bit of torque for that weight vehicle. You forgot to adjust your result for the 96 ft-lb motor for effects of drive train efficiency and inertia. The inertia factor I used is C sub i = 1 + 0.04 + 0.0025*g^2, where g is the overall gear ratio. It is given on page 99 of the second edition of Bob Brant's book, and is an approximate estimate of inertial effects using equivalent mass. For your car in first gear it would be about 1.52. Then for the 96 ft-lb motor you get about 6 mph/sec. So difference of 14.4 - 6 = 8.4 mph/sec. Edit: These are just estimates. For my car the calculation came out to 7 mph/sec in first up to around 20 mph and dropped to about 6 mph/sec at 25-30 mph. The data logging gps showed a steady 6 mph/sec up to a bit over 25 mph, where I shifted. So it agreed fairly well.


----------



## sholland (Jan 16, 2012)

tomofreno said:


> That is quite a bit of torque for that weight vehicle. You forgot to adjust your result for the 96 ft-lb motor for effects of drive train efficiency and inertia. The inertia factor I used is C sub i = 1 + 0.04 + 0.0025*g^2, where g is the overall gear ratio. It is given on page 99 of the second edition of Bob Brant's book, and is an approximate estimate of inertial effects using equivalent mass. For your car in first gear it would be about 1.52. Then for the 96 ft-lb motor you get about 6 mph/sec. So difference of 14.4 - 6 = 8.4 mph/sec.


Yeah, it was a blast to drive!!

Working backwards, I need would that mean 8.4mph/sec / 2.237 = 3.76m/sec^2, 3.76*1350*0.293 = 1487N-m or 1097ft-lb.

So, for an AC50 @115ft-lbs I would need ~9.54:1 gear reduction.

That would give me the boost I want, but only gets me to 60mph then the AC50 would have be disconnected or a 2nd gear would be needed.

Does that seem right?


----------



## tomofreno (Mar 3, 2009)

sholland said:


> Yeah, it was a blast to drive!!
> 
> Working backwards, I need would that mean 8.4mph/sec / 2.237 = 3.76m/sec^2, 3.76*1350*0.293 = 1487N-m or 1097ft-lb.
> 
> ...


 The AC50 is only 90 ft-lb peak, out to about 3000 rpm at 96V nominal, about 3900 - 4000 at 115V nominal. The AC31 is about 117 ft-lb peak, but only out to about 1800 rpm at 96V. I don't see how you could do it without at least 2 gears. Looks like 60 mph is about 880 wheel rpm on your car, so you would be limited to about 4.5:1 to maintain peak torque on the AC50 out to that speed if you use a 115V pack, which would only give you 405 ft-lb wheel torque. If you used 12:1 to get 1087 ft-lb wheel torque at peak motor torque, you would only have it out to about 25 mph or less. Sounds complex to get everything to work even if you find a motor with suitable torque.


----------



## sholland (Jan 16, 2012)

Hmm, I might still shoot for the 60mph option with 2 AC20's for a combined wheel torque of about 675ft-lb to maybe 40mph then tapering to 320ft-lb or so at 60mph. Still a respectable addition in thrust. 2 AC31's would of course be better, but the combined price is going to getting kinda high...

Those numbers of course would be to get a good hole-shot with combined ICE and electric power, while still offering reasonable acceleration of ~3mph/sec on electric alone to ~40mph.

The CR-V diff has a clutch which I can just have opened above 60mph. The CR-V diff is 2.529:1, so I still need additional reduction. I'll just have to get something fab'd up...


----------



## sholland (Jan 16, 2012)

I also just found a Nissan Rogue AWD rear differential that has an electrically actuated clutch and 5.173:1 ratio. Almost ideal...


----------

