# Inline drives



## major (Apr 4, 2008)

Hawks said:


> Hi guys, sorry if this is located somewhere else too, I tried looking around but couldn't find anything. If this belongs somewhere else or is already discussed elsewhere, then please just give me a kick in the right direction.
> 
> Anyway, I was wondering the possibility of doing an inline drive motor in the back axle rather than hooking it to the transmission. Some pros I could think of would be:
> -Less friction, greater efficiency
> ...


It is a bad idea which has been discussed numerous times. Recently near the end of this thread: http://www.diyelectriccar.com/forums/showthread.php/15-car-hub-motor-799-52336.html


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## Hawks (Dec 12, 2012)

Major, I would like you to read this page

I personally think it is hysterical that you would go and call it a "bad idea" when it has barely even been attempted, and certainly not perfected. I'm surprised you are even interested in EVs with that attitude, because most people I know dismiss EVs as bad ideas


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## mizlplix (May 1, 2011)

Actually, he is generally correct. 

The idea that a regular EV motor can be just bolted up and get both the low RPM torque and the high RPM needed to have any decent road speed, IS bad.

It needs a lot of money, very light weight car, a gearbox not easily available, a high rpm motor not easily available and flat terrain.

(and your comments are a little harsh)

Miz

PS: My car is direct drive...I know what I am talking about. It requires perfect gearing, motor torque curve and flat terrain if you want any sort of range, something a Noob is not likely to hit right the first time.


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## major (Apr 4, 2008)

Hawks said:


> Major, I would like you to read this page
> 
> I personally think it is hysterical that you would go and call it a "bad idea" when it has barely even been attempted, and certainly not perfected. I'm surprised you are even interested in EVs with that attitude, because most people I know dismiss EVs as bad ideas


Kool  Running the motor(s) at wheel (axle) speed is a bad idea. Direct drive, like Miz mentions, still has a reasonable reduction and works well for electric motors. 

I'm glad you're amused with my response. Let us know how those inline motors work out for you.


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## Hawks (Dec 12, 2012)

So everything not practical at this given moment is a bad idea?

If we just dismissed everything that didn't work out on the first try, we wouldn't even have electric vehicles! From what I have read from you, major, on other threads, I see nothing inherently flawed about inline drive, just that current motors are really not capable of handling it, and there are no solutions yet to solve that issue. Not too many years ago, EVs were impractical because there were no capable batteries, but that problem has been well addressed.

mizlplix, if that was aimed at me, what was harsh about my comments?


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## major (Apr 4, 2008)

Hawks said:


> So everything not practical at this given moment is a bad idea?


Maybe not everything. But impractical does pretty much define bad idea. Bad idea = impractical. In my book, but I tend not to sugarcoat stuff. 

So you figure out a way to make a motor work at wheel speed as well as a gear reduced motor and prove me wrong. Go ahead, make my day. After that, I'll change my mind and won't call it a bad idea any longer.

But right now, it is a bad idea


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## Siwastaja (Aug 1, 2012)

I think many people on this forum have their feet strongly on ground. They want to see results instead of talk. They want to use parts that you can buy now. It may look pessimistic, but in the end, it is the right way. I guess it can motivate, too, to prove them wrong.

Most people here are oriented towards the idea that as many people as possible could make simple EV conversions as easily as possible, using off-the-shelf products. This is why DC motors are generally preferred here over technically superior AC motors, too; traditional DC motors and controllers just are more easily available for DIYers, and many people have hands-on experience on them. This is an important point.

I believe that direct wheel drive and even hub motors WILL have real future in them, but they need some more engineering. Everyone wants this to be proven true.

Electronic 4WD will be the big thing in the future, that's for sure. Whether it will be direct wheel drive low-rpm hub motors, low-rpm drives at CV joints, or a high-rpm drive with integrated reduction gearing, is to be seen. I vote the last one. Note that a fixed reduction gearing is much simpler compared to a transmission or a differential. 

Electric 4WD is superior in all regards; it gives _really_ good driving characteristics compared to any mechanical limited-slip differential, and without the energy consumption drawback of the mechanical solutions. Although there are 4 motors and controllers, they are all identical and relatively small. Electronics like to be divided in small modules and copied over and over again. Four 20 kW drives are not much more "complex" than one 80 kW drive. Note that the number of sold units is very important when determining price. If every customer buys 4 small controllers instead of 1 large, the _total_ price of the 4 controllers will be near the price of 1 large.

But this is only talk. It is not a viable solution for anyone who wants to convert their car now. We have a lot of engineering work to do to improve the concepts and make them products.


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## subcooledheatpump (Mar 5, 2012)

If you do want to convert a vehicle right now though, the closest you can probably get is going right from a motor to a drive shaft on a rear wheel drive vehicle. That has been done plenty of times. No transmission so no clutches to wear or gear changes that interrupt torque. 

I have some ideas myself about a system, similar to what Siwastaja mentioned, a 4 wheel drive system with a motor, and a shaft for each wheel. Then each wheel would have its own planetary reduction system built in that transfers power between the shaft and the wheel.

I've also thought about a locomotive style system, a wheel with a shaft and a gear attached, then having an electric motor with another gear mesh with the gear on the shaft. Grease the gears then install a dust cover. no more oil or oil seals to deal with


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## Hawks (Dec 12, 2012)

Well, I have done a fantastic job of steering this thread to the ground, what a poor way to introduce myself here.

I do have an additional tech kind of question here, my probable conversion car is a small mid-80s Toyota Pickup, and a design goal would be to get the engine out of the way of the front and cab to allow for maximum room for batteries and such. If an inline drive system is not practical, is there any other way to mount the engine in the back?


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## Siwastaja (Aug 1, 2012)

Hawks said:


> I do have an additional tech kind of question here, my probable conversion car is a small mid-80s Toyota Pickup, and a design goal would be to get the engine out of the way of the front and cab to allow for maximum room for batteries and such. If an inline drive system is not practical, is there any other way to mount the engine in the back?


If it is a RWD, a good idea would be to direct drive to the rear differential. You see, the diff _has_ a reduction gearing in it. We are doing exactly this in our conversion of a Mitsubishi L200 pickup. It _may_ be possible to directly replace the transmission with the motor, if it physically fits. In this case, you would have the engine compartment free for batteries and stuff. Put the batteries as low as possible, and you will have an extra dry compartment for luggage etc.

In case of pickup, you also have a lots of room below the bed; at least the space left behind by the exhaust, muffler and fuel tank. Put some of the batteries near the rear wheels so that you have enough traction in slippery conditions.


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## Electroddy (Dec 29, 2009)

Hawks said:


> I do have an additional tech kind of question here, my probable conversion car is a small mid-80s Toyota Pickup, and a design goal would be to get the engine out of the way of the front and cab to allow for maximum room for batteries and such. If an inline drive system is not practical, is there any other way to mount the engine in the back?



Look for an early Taylor Dunn golf car. They have a narrowed Ford 9" rear end. The motor is mounted on top of the housing, and uses a silent chain drive as the first reduction. A Toyota truck has plenty of room to duplicate the layout.


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## major (Apr 4, 2008)

Hawks said:


> I do have an additional tech kind of question here, my probable conversion car is a small mid-80s Toyota Pickup, and a design goal would be to get the engine out of the way of the front and cab to allow for maximum room for batteries and such. If an inline drive system is not practical, is there any other way to mount the engine in the back?


Hi Hawks,

Please call it a motor if you are referring to the electromechanical device. And engines for those smelly things we wish to replace 

You can mount the motor anywhere you want. I'd advise not to mount it to the axle itself. The axle is unsprung...that's why it rides like a truck. Adding mass to the axle makes it worse. But you can shorten the drive shaft and move the motor closer to the rear. Study the geometry of the driveshaft so you don't end up with vibration. I have even seen one guy mount the motor to the rear of the axle.

If you go direct drive (that is eliminate the transmission), see if you can get a rear end with a high ratio (numerically). Otherwise you'll need a larger motor or higher current limit to get acceptable launch acceleration and hill climb. And then beware of motor heat at long slow speed use. You may have to use forced ventilation.

Personally I like direct drive. But it is often much easier for newbie converters to use the existing manual tranny. And that works very well. In a pickup truck, it would seem you have plenty of space under the bed for battery and that puts the weight to the rear where you'd want it.

Good luck,

major


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## Duncan (Dec 8, 2008)

Hi Hawks

The problem with direct drive is - achievable torque is roughly proportional to weight

this is a (very) crude approximation

The minimum torque needed at the (rear) wheels is ~ tire radius x 20% (any less and hills become impossible) of vehicle weight

so for a 2000lb car with 1ft radius = 400lbft

motors able to produce 200lbft (because there are two - one on each wheel) weigh over 400lbs - each

Now direct drive to the differential means that you can use the torque multiplication in the diff - mine is 4.1 : 1

Now to get 400ftlbs wheels = 100ftlbs motor
A motor able to produce 100ftlbs weighs ~ 200lbs 

So one 200lb motor + one 50lb diff = 250lbs

or two 400lb motors = 800lbs


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