# Couple Motor Directly to Differential?



## sharp21 (Mar 11, 2008)

Is that possible & what would the pro's & cons be?

I realize that you would need careful gear selection... Or potentially you could use an over/under gear splitter?

A buddy of mine builds killer golf carts with a transaxle, which is what got me thinking about something like this for a T style hot rod.

S.


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## Woodsmith (Jun 5, 2008)

You would need to carefully consider the gear ratios available and the speed range that you require.

Other things to consider would be reversing. A high speed, high voltage motor would more then likely have advanced brush timing and so may not reverse well.

Also, is the diff on a live axle or is it an independent suspension set up?
If you mount the motor on a live axle then it will be additional unsprung mass and the motor and its mounting to the axle will be subject to a lot of road shock and vibration.
An independent suspension set up would lend itself much more easily.

I came across a race diff that had quick swappable gear ratios and a reversing gear so the diff could be run in either configuration. With hindsight the maker would have been useful but I neglected to check as I didn't need one and it was too costly for my possible requirements.


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## poprock (Apr 29, 2010)

Woodsmith said:


> You would need to carefully consider the gear ratios available and the speed range that you require.
> 
> Other things to consider would be reversing. A high speed, high voltage motor would more then likely have advanced brush timing and so may not reverse well.
> 
> ...


 Hi; Poprock here; I have done this with a 89 L series Subaru sportswagon with a 3.7:1 diff. The sub has the diff mounted to the body and I made a short tailshaft and mounted the motor where the rear tailshaft was. Ratio is way too high; needs a 4.4:1 from a Brumby ute? I have left the FWD fully operational; it will take off slowly on level ground, but on a slope I start off with FWD. 40kmh is all it will do on level ground. The motor is the 36V forklift I had in my Hillman Hunter;which Woodsmith would remember. I put it back to original and sold it to a keen restorer. The sub is using 3 contactors with 4 6v forklift batteries on #1, switching to 2 12v forklift batteries on#2 and adding two 12v car batteries on #3. Very few cars today would have a lower diff ratio than 4:1 so the gearbox method is better for a small motor like mine.


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## sharp21 (Mar 11, 2008)

My buddy builds golf carts & the motors couple right to the axle, which is why I was asking.

I suppose a rear engine transaxle from a fiero or VW would work as well. I've been thinking about a Model T style EV. Has anyone here built something like that?
S.


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## Woodsmith (Jun 5, 2008)

One of the things with golf buggys is that they have much smaller and lighter axles and run slower. They also don't need the same road holding and handling that a road vehicle would need.

Have a look at Toddshotrods thread. He is building a T hotrod. Someone else mentioned a wanting to do a T conversion but seems to have gone quiet.

It may be easier to just have a propshaft between the motor and a live axle so that the motor can be mounted to the chassis frame where the transmission would normally be. This is the thinking behind the Transwarp9 motor from Netgain.


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## nimblemotors (Oct 1, 2010)

A fixed-gear ratio is a problem for a freeway capable EV.
Zero to 70mph is too broad a range for a single gear to be effective, unless you have an overly powerful motor to accelerate from a stop with,
or put up with poor performance. A 2-speed trans is ideal, and having reverse is also quite useful for a DC motor. A common manual 4-5sp transmission isn't really that heavy. 
The 4-speed out of my MG midget is only 50lbs.


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## Crash (Oct 20, 2009)

This is something I'd like to do at some point. In C5 Corvettes, the transmission is in the back linked directly to the differential. So I'd love to go direct drive with the motor bolted directly to the diff. The motor could use the stock transmission mounts plus some reinforced mounts. That would leave lots of room under the hood for batteries and other important electronics.


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## toddshotrods (Feb 10, 2009)

Woodsmith said:


> ...Have a look at Toddshotrods thread. He is building a T hotrod...


Huh? Someone call me? 

If you want to build a conventional "Fad T" or traditional style Model T, using a driveshaft from the motor to a solid rear end is the way to go. T's are very lightweight, because there's not much there, so you'll have an easier time running direct drive than most. With the right size motor and the right batteries, accelerating from a stop shouldn't be a problem - even with it geared for highway speeds.


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## nimblemotors (Oct 1, 2010)

the c5 has the trans integrated with the diff, costly to machine a coupling. If you're going that way, the c4 has a std rear diff, must easier to couple to that. 

Interesting to mention the corvette, because the C4 with the 4+3 transmission was a 4-speed with an electrically activated planetary overdrive attached to the back. I had an 84, and my plan was the use just the overdrive with electric motor, so it'd have a two-speed setup.
Didn't have room for the vette when I moved, so project was never done.


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## sunworksco (Sep 8, 2008)

You can couple direct with a 9-1 gear ratio Speedway Engineering differential.
New Venturi EV using this side-winder design.
Sweet !!
Regards,
John


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## Crash (Oct 20, 2009)

nimblemotors said:


> the c5 has the trans integrated with the diff, costly to machine a coupling. If you're going that way, the c4 has a std rear diff, must easier to couple to that.
> 
> Interesting to mention the corvette, because the C4 with the 4+3 transmission was a 4-speed with an electrically activated planetary overdrive attached to the back. I had an 84, and my plan was the use just the overdrive with electric motor, so it'd have a two-speed setup.
> Didn't have room for the vette when I moved, so project was never done.


Yeah, a coupler would be expensive to make, however it would be far more efficient and simple in the long run. Since the car is already setup to handle torque at the differential location, it'd just be a matter of designing the right input/output shaft. I believe that the output shaft on the Corvette's transmission is a 29 spline (I could be wrong on the number) that mates directly to the differential, rather than the differential having it's own input shaft. If that's the case, it's a matter of having the correct output spline on the motor and mating the motor to the diff with an adapter plate. The adapter plate would have to be very specially engineered because the stock transmission seals the diff fluid in the diff.

It can be done, and if done correctly, would yield far better results than using a transmission. (Efficiency wise)


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## Bags (Jun 20, 2010)

I just bought it, I didn't build it, but FWIW: 

My car has direct drive plus a Gear Vendors overdrive. If I recall correctly, overdrive is 0.76:1. 5.11 rear end. Typically go from 0-40mph in direct drive, then click in the overdrive. Electrically operated by foot switch. Haven't taken it past 70mph yet. ;-) Still a little porky for autocross, but at least I didn't come in last. Very pleasant system for daily driving.


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## JRP3 (Mar 7, 2008)




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## JRP3 (Mar 7, 2008)

Bags said:


> I just bought it, I didn't build it, but FWIW:
> 
> My car has direct drive plus a Gear Vendors overdrive. If I recall correctly, overdrive is 0.76:1. 5.11 rear end. Typically go from 0-40mph in direct drive, then click in the overdrive. Electrically operated by foot switch. Haven't taken it past 70mph yet. ;-) Still a little porky for autocross, but at least I didn't come in last. Very pleasant system for daily driving.


That sounds like a really cool setup. 0-60?

Never mind, I found it, 5.9! Nice. http://www.evalbum.com/120


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## Bags (Jun 20, 2010)

Yes, that evalbum page and time was the previous owner. Not sure if that 0-60 time was with the previous 144v battery setup or the current 156v setup. Haven't timed it myself yet. Also holds the NEDRA record at 144v.


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