# opel calibra direct drive



## santar (Mar 8, 2011)

Hi people,
this is me first post here, im not naturally english speaker. So pleasse apologize some mistakes and pleasse try to understand me😕.
I'm planing to convert my calibra 4wd to rwd with ac 75 motor direct on rear diff which is now 3.7 ratio. What do you think about this? Will be the ac75 enough powerfull to drive the car about 140 kmh? Or have i to change the pinion and ring to other ratio?
Thanks for replies


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## dougingraham (Jul 26, 2011)

If we assume a 2 ft diameter tire (61 cm) with a 3.7:1 final drive and no transmission we would expect to see peak power at 4500 RPM which equates to a vehicle speed of 140kph (86.8 mph). I don't see any reason to think it would not reach that speed when using the 144V 500 amp Curtis controller if equipped with a battery that can do 144V and 500 amps.


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## santar (Mar 8, 2011)

Thanks for your reply. I have the 96 volt controller, it makes any difference in the max speed and acceleration?
Is here somebody with the experience direct drive by ac 75?


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## dougingraham (Jul 26, 2011)

The voltage will determine the torque band so yes it will make a difference in the max speed. The current limit will determine the torque.

Direct drive is a tricky business for a conversion. The car will feel sluggish off the line but about the time you would have been in third gear it will feel great.

With 96 volt 650A controller your power peak occurs at about 2500 RPM at 79 HP and with the 144 volt 500A controller it occurs at about 4500 RPM at 92 HP.

If you have the high current version of the controller you will see reasonable accelleration up to that 2500 RPM point and it will still be better than the high voltage controller up to about 3200 RPM and above that RPM the high voltage setup is more powerful. When driving you will feel like someone pulled your foot off the throttle when you reach that 2500 RPM with the low voltage controller. Max power at 4500 RPM with the low voltage controller is maybe 52 HP so you might not ever even get there and if you do it could take a long time to make it.

My calculations show that it would be usable with direct drive on the high voltage controller and not great on the 96 volt one. But if you are expecting Tesla performance you wont be getting anything like that.


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## santar (Mar 8, 2011)

Thank you very much for your replies dougingraham looks that you are very experienced.
Can you also pleasse count the 0-100kmh for me? The final weight will be some 1400 kg and the drag coef. will be about 0.22.


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## santar (Mar 8, 2011)

I have foud this nice calculator
http://evthoughts.blogspot.sk/2011/10/vehicle-speed-calculator-mark-2now-with.html?m=1
and it looks that 0-100 will be some 10 s.
I think good enough for daily driving. Maybe in future will ad some smaller motors on each half axe.


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## dougingraham (Jul 26, 2011)

santar said:


> Thank you very much for your replies dougingraham looks that you are very experienced.
> Can you also pleasse count the 0-100kmh for me? The final weight will be some 1400 kg and the drag coef. will be about 0.22.


I am only experienced in the sense that I have converted one car and I am in the planning stage on a second. I know a little bit about the physics, the electrical engineering and the mechanical engineering that goes into this. 

I have written a single reduction ratio acceleration simulator that does not include air drag or rolling resistance yet. The model is overly optimistic and shows a 0-100kph time of about 15 seconds for a vehicle with your mass and an AC-75 power train on a 96 volt 650 amp controller. You should reach 140kph in about 22 seconds. The same setup on the 144 volt 500 amp controller shows a 0-100kph time of about 20 seconds. You reach 140kph at 28 seconds in this case. And while this is worse I believe the road feel would be better. Different final drive ratios change these things quite a lot. Unfortunately changing this is somewhat involved on most cars. Changing to a 5.5:1 ratio gives 14 seconds for the 0-100kph on the 144 volt controller and 0-140kph time of 21 seconds. The low voltage controller does 12 seconds for 0-100kph and 22 seconds for 0-140kph. Keep in mind that these times are going to be optimistic. Assumptions were HPEVS dyno plot data, 61cm diameter tires, vehicle mass with driver of 1454 kg.

I have not personally used an AC-75. I have ridden in a couple of direct drive cars and if you have a light enough vehicle with enough torque and a wide enough torque band with the right gearing you can get an excellent result. I am not sure that with a car of this mass with this motor/controller combo you will be happy without a gearbox. It is all about expectations. If you keep the gearbox the car is a lot quicker at the bottom end.

Best Wishes!


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## santossrg (Jan 6, 2016)

dougingraham said:


> If we assume a 2 ft diameter tire (61 cm) with a 3.7:1 final drive and no transmission we would expect to see peak power at 4500 RPM which equates to a vehicle speed of 140kph (86.8 mph). I don't see any reason to think it would not reach that speed when using the 144V 500 amp Curtis controller if equipped with a battery that can do 144V and 500 amps.


And what is the rated torque of an AC-75?

Can this motor handle the vehicle weight in an 10% incline plan?

Best Regards.


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## dougingraham (Jul 26, 2011)

santossrg said:


> And what is the rated torque of an AC-75?
> 
> Can this motor handle the vehicle weight in an 10% incline plan?


In the flat portion of the curve the AC-75 was 183 lb-ft at close to zero rpm dropping down to 168 lb-ft at 2500 rpm at 650 motor amps. See the dyno chart here. AC-75 Power Graphs

But this discussion is moot now since HPEVS has discontinued the AC-7X series motors. I believe that since they were sealed motors they could not get rid of the excess heat over the long term. The most practical approach is one of the Siemens or UQM motors and eventually a Nissan Leaf or Tesla power train from a salvage vehicle. As for the HPEVS stuff it is all ultimately power limited by the Curtis Controller to somewhere between 80 and 90 HP per controller. This is more than adequate for a 2 seat sports car in normal city driving conditions. And the dual AC-35 is around 160 HP.

For your 10% incline question... 183 ft-lb * 3.7 final drive gives 677 lb ft at the face of a 24 inch diameter tire. So it looks like a 10% grade should be possible.


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