# Direct to wheel drive



## MalcolmB (Jun 10, 2008)

The main problems with that approach are

a) finding a motor that will deliver sufficient torque and a sufficient range of rpm.

b) compromised handling since the motors add to the unsprung weight.

c) compromised motor reliability, since all road shocks are transmitted directly to the motors.

The simplest way to eliminate these problems is to couple the motors to the inboard ends of the driveshafts via some form of gear reduction, like this: http://www.rimac-automobili.com/concept_one/propulsion-system-8


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## Bertzie (Oct 13, 2011)

Due to the design of the vehicle in question, mounting the motors within the suspension would be essentially impossible without the use of several 90 degree turns, which would greatly reduce efficiency and power. Each wheel will be mounted on the end of an S-shaped arm to allow for independent control of its height. 

A couple websites promise that the TransWarP 9 motor would provide adequate torque at 1000amperes. (The site claims 237ft lbs, which with two motors would give me 474).

Would it be possible to create some sort of independent suspension just for the motor on the arm, to reduce motor wear?

(I apologize for the crudity of the drawing)


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## gor (Nov 25, 2009)

no 90 dgr turns


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## Bertzie (Oct 13, 2011)

How much torque you reckon one of those chains can take?


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## lutach (May 31, 2011)

Bertzie said:


> Did a forum search for this, but turned up nil, so I figured I'd start a thread.
> 
> Most direct drive threads seem to assume a single motor to axle to drive wheels. Now what I'm thinking is, two motors coupled directly to the drive wheels. What I'm figuring would be the best rout would be to use a spline on the motor directly to the wheel hub assembly. Would that work? And has anyone done that, or have any experience with it? I know the Jaguar C-X75 concept uses individual wheel drive motors, but I don't think they'd be too keen on giving me their secrets.


The Jaguar C-X75 will not use the 4 motor layout as it was stated, the production version will only use 2 motors and an I.C.E. engine hooked up to a generator. The only vehicle that I know that has successfully done this is the Eliica.


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## MalcolmB (Jun 10, 2008)

Bertzie said:


> How much torque you reckon one of those chains can take?


Torque capacity is not generally the limiting factor when choosing chain drive. The Killacycle drag bike uses 630 motorcycle chain to transmit 500 hp and accelerate at almost 3G.

The main consideration is how quickly the chain will stretch or wear.

If you could tell us a little more about your particular application we might be able to offer more suggestions


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## Bertzie (Oct 13, 2011)

MalcolmB said:


> Torque capacity is not generally the limiting factor when choosing chain drive. The Killacycle drag bike uses 630 motorcycle chain to transmit 500 hp and accelerate at almost 3G.
> 
> The main consideration is how quickly the chain will stretch or wear.
> 
> If you could tell us a little more about your particular application we might be able to offer more suggestions



Well, to put it simply, I want to build a replica of the Light Runner from Tron: Legacy. The problem I see with the Killacycle comparison is this. While it puts out a tremendous amount of torque, the bike itself only weighs 650lbs. And while I don't know the exact size, I am 100% certain the tires I'll be using for this project are MUCH larger. (If I remember correctly, the Killacycle has 10x27 drive wheel. The wheels I plan on using are 18x32) Thankfully since I'm essentially broke right now, I have lots of time to engineer the crap out of this.


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## Bertzie (Oct 13, 2011)

Upon reflection, I realized something. I could just use double, (or even triple) drive chains. The Killacycle moves 650lbs at 2,000ft lbs of torque. Using 3 chains per drive wheel, I could (theorectically) move 3900lbs at 12,000ft lbs of torque. It would also give me the ability to gear the RPMs down by 2-3:1, which would be much easier on the motors.

What do you guys think of that idea?


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## MalcolmB (Jun 10, 2008)

Interesting project.

Yes you can use duplex or triplex chain. I'm using duplex chains on my Mini as the limited space meant I had to use chain with a smaller pitch than usual.

With a little modification to the design of those swingarms you could house the chains inside them, so they're hidden and protected. I'm curious though, those wheels are obviously going to be heavy, but where does the rest of the 3900 lbs come from? If you could reduce your total weight it would make things a lot easier.


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## Bertzie (Oct 13, 2011)

MalcolmB said:


> Interesting project.
> 
> Yes you can use duplex or triplex chain. I'm using duplex chains on my Mini as the limited space meant I had to use chain with a smaller pitch than usual.
> 
> With a little modification to the design of those swingarms you could house the chains inside them, so they're hidden and protected. I'm curious though, those wheels are obviously going to be heavy, but where does the rest of the 3900 lbs come from? If you could reduce your total weight it would make things a lot easier.


I'm making an assumption that I'll be using every pound. This way, when it comes to practical application, I'll have more applied performance. I'd rather too much power than too little. I'd ideally like to find some way to put a generator on board for a hybrid vehicle, but for this phase of design I'm sticking to just electric propulsion. 

The motors I'm hoping to use are 2 TransWarP 9, (or something similar) due to their spline connections, which I'm familiar with. Don't know too much about key shafts. Also, the TransWarp series doesn't require a transmission, though I'm not sure what they qualify as a transmission. Each motor is rated for a vehicle of 1800lbs. Combine that gives me 3600lbs to work with.

The motors each weigh 150, so that's 300lbs right there. Each tire+wheel is 100lbs, so that's 400lbs. About 1,000 for a battery pack, (Though if I can swing the generator idea eventually that would be much smaller) So working right now that's 1700lbs. Basing on what I've got now, that'll leave me 1900 for the rest of the vehicle, plus passangers. (And I'm a big guy with big friends, so figure 1400 for the vehicle, plus 500 for passangers).


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## major (Apr 4, 2008)

Bertzie said:


> ....though I'm not sure what they qualify as a transmission. Each motor is rated for a vehicle of 1800lbs.....


Typically, the context around here is: Transmission = device between motor and wheels capable of multiple ratios. Direct Drive = a fixed ratio between motor and wheels.

And motors are seldom, if ever, rated for vehicle weight. Don't know why or where that comes from. Many guys use the 9" motors in EV cars way over 1800 lbs.


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## Bertzie (Oct 13, 2011)

http://www.evsource.com/tls_transwarp9.php

Those are just recommended numbers of course. I'd really really really really like to avoid using a multi-ratio transmission. Mainly because those are complicated.

Edit: It's the Trans WarP 9 that's rated for 1800lbs. The regular WarP 9 is rated for 3600.


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## major (Apr 4, 2008)

Bertzie said:


> It's the Trans WarP 9 that's rated for 1800lbs. The regular WarP 9 is rated for 3600.


It's the same motor, just different mechanicals (shaft, etc).


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## dougingraham (Jul 26, 2011)

Bertzie said:


> http://www.evsource.com/tls_transwarp9.php
> 
> Those are just recommended numbers of course. I'd really really really really like to avoid using a multi-ratio transmission. Mainly because those are complicated.
> 
> Edit: It's the Trans WarP 9 that's rated for 1800lbs. The regular WarP 9 is rated for 3600.


These are the same motor, just the shaft that is different. The reason for the different weight suggestions is if you dont have a transmission your acceleration will be sluggish at the higher weight and the Trans WarP are intended to connect directly to a drive shaft.

In a direct drive situation the motor red line will limit the top speed in association with the final drive ratio. An example of this would be a calculation I did a couple of days ago when my batteries arrived. One of the guys said lets put your motor and batteries on a go cart. I said what is the wheel diameter? They are about 8 inches in diameter and if you direct drive the wheel the RPM limit of the WarP 9 motors is 5500 RPM. An 8 inch wheel at 5500 RPM advances about 25 inches per turn. That is 137500 inches in a minute and 8250000 inches in an hour. Convert this to miles and you get 130 mph give or take a little bit.

It seems to me that if you don't want a transmission for simplicity you still will need a reduction because you want to be able to run the motor up to red line in order to take advantage of the full range. The question is how fast do you need to go and you have to be reasonable here. If 90mph is reasonable then the second question is what diameter are your tires. This will be driven by the looks of the vehicle you are trying to reproduce. Lets say that those are 3ft diameter tires and you want to be able to go 90mph at redline. This means the car will move forward 113 inches per revolution. 90mph is 95040 inches per minute and thus 841 wheel RPM with 3 ft diameter tires. To attain this with 5500RPM is a reduction ratio of 6.54. The good thing about reducing the RPM is that you are multiplying the torque by the same amount.

Have fun working the numbers!


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## Bertzie (Oct 13, 2011)

dougingraham said:


> These are the same motor, just the shaft that is different. The reason for the different weight suggestions is if you dont have a transmission your acceleration will be sluggish at the higher weight and the Trans WarP are intended to connect directly to a drive shaft.
> 
> In a direct drive situation the motor red line will limit the top speed in association with the final drive ratio. An example of this would be a calculation I did a couple of days ago when my batteries arrived. One of the guys said lets put your motor and batteries on a go cart. I said what is the wheel diameter? They are about 8 inches in diameter and if you direct drive the wheel the RPM limit of the WarP 9 motors is 5500 RPM. An 8 inch wheel at 5500 RPM advances about 25 inches per turn. That is 137500 inches in a minute and 8250000 inches in an hour. Convert this to miles and you get 130 mph give or take a little bit.
> 
> ...


Actually, you just worked the numbers for me. (Well, close enough, my tires are going to be 32", not 36"). The TransWarp 9, (according to this site http://www.evsource.com/tls_transwarp9.php ) has a continuous opperating RPM of 3500, with a redline of 5500. Running at 3500 rpm, with a gear ratio 6:1 with 32" tires will give me a speed of 111.1mph. And if the torque is right from that site, at 300amps, (which, if I use their WarP-Drive controller, should be no problem) with the 6:1 ratio, will give me 355.8ft lbs of torque. (And since I intend on using two motors, that'll be 711.6ft lbs of torque over all.

And this might be a useful tool for other builders, http://wahiduddin.net/calc/calc_speed_rpm.htm You put in the motor RPM, transmission/differential ratios, and wheel size. Pops out the MPH.

Sneaky edit: How hard/expensive is it to change the shaft from keyway to spline? Would it cost more than the $400 more that the TransWarP costs over the regular WarP 9?


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## Coulomb (Apr 22, 2009)

Bertzie said:


> ... if I use their WarP-Drive controller, should be no problem) with the 6:1 ratio, will give me 355.8ft lbs of torque. (And since I intend on using two motors, that'll be 711.6ft lbs of torque over all.


Something to consider: most sedans have about a 12:1 ratio in first gear (3:1 transmission, 4:1 diff, give or take). So 80 ft.lbs from the motor (say) becomes 960 ft.lbs, which is useful for climbing gutters and the like. Will 700 ft.lbs be enough at the low end?

This is the trade-off you always get with direct drive: will you have enough speed at the top end, and enough torque at the low end? Because you can't change the ratio to trade one for the other. So you typically end up with a larger motor than you otherwise would need.

It can still be better overall; the larger motor is offset by the weight, space, and losses of the transmission. A higher voltage system (e.g. 156 V or more) is advantageous with direct drive, since you can get higher RPM from the motor at the top end, so you can use a higher ratio diff (shorter?) and get more torque at the bottom end for the same top speed, or just have more room to juggle the top speed verses bottom torque compromise.


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## Bertzie (Oct 13, 2011)

Coulomb said:


> Something to consider: most sedans have about a 12:1 ratio in first gear (3:1 transmission, 4:1 diff, give or take). So 80 ft.lbs from the motor (say) becomes 960 ft.lbs, which is useful for climbing gutters and the like. Will 700 ft.lbs be enough at the low end?
> 
> This is the trade-off you always get with direct drive: will you have enough speed at the top end, and enough torque at the low end? Because you can't change the ratio to trade one for the other. So you typically end up with a larger motor than you otherwise would need.
> 
> It can still be better overall; the larger motor is offset by the weight, space, and losses of the transmission. A higher voltage system (e.g. 156 V or more) is advantageous with direct drive, since you can get higher RPM from the motor at the top end, so you can use a higher ratio diff (shorter?) and get more torque at the bottom end for the same top speed, or just have more room to juggle the top speed verses bottom torque compromise.


Well, that 700ft lbs was at 300 amps. The controller I'm looking at is rated upto 1000. At 1000 amps, the motor is rated for 237ft lbs. At a 6:1 ratio, that's 1422ft lbs per wheel, 2844ft lbs total. Now, if my understanding of the system is correct, (And lord willing it might be) I should only need that torque when accelerating and climbing hills, after which it should drop back down, correct?


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## major (Apr 4, 2008)

Bertzie said:


> .....Running at 3500 rpm, with a gear ratio 6:1 with 32" tires will give me a speed of 111.1mph.....


Looks like you're off by a factor of 2.



> Sneaky edit: How hard/expensive is it to change the shaft from keyway to spline? Would it cost more than the $400 more that the TransWarP costs over the regular WarP 9?


You might explore other options before doing a hack job on the motor shaft to save a couple hundred $. Maybe use a taper-lock? But from what I see you have not yet defined what the motor couples to.


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## Coulomb (Apr 22, 2009)

Bertzie said:


> At 1000 amps, the motor is rated for 237ft lbs. At a 6:1 ratio, that's 1422ft lbs per wheel, 2844ft lbs total.


Ok, that should do it  But 6:1 seems too short for decent top speed.



> Now, if my understanding of the system is correct, (And lord willing it might be) I should only need that torque when accelerating and climbing hills, after which it should drop back down, correct?


Yes, sure. It's nice to have at all times, but the motor would quickly overheat. Note that 1000 A to two motors (2000 A from the pack) will demand a lot from the pack, too; it won't be able to supply this power for long.


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## Bertzie (Oct 13, 2011)

major said:


> Looks like you're off by a factor of 2.


I didn't do the math. This thing did. http://wahiduddin.net/calc/calc_speed_rpm.htm Engine speed of 3500rpm, transmission ratio 6:1, differential ratio 1:1, wheel size 32 inches. If you have different math, please share it.



major said:


> You might explore other options before doing a hack job on the motor shaft to save a couple hundred $. Maybe use a taper-lock? But from what I see you have not yet defined what the motor couples to.


Well, it really depends on the cost difference, and whether or not it'd be worth it. The WarP 9 is $1800. The TransWarP 9 is $2200. I have no intention on just slapping it together halfheartedly.

With the current incarnation, the motor would turn a drive shaft with sprockets that turn chains that turn other drive shafts that turn the wheels. The only real difference at this point is how the motors would connect to the sprocket drive shaft. And between the motors, the TW9 would be spline to yoke to shaft, where as the WP9 is keyway to yoke to shaft. To my knowledge, splines are stronger. But if the efforts and finances to add a spline shaft to the WP9 are too excessive, (which at this point it sounds like they would be) I'll just use the TW9, since it's already set up with a spline.


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## Bertzie (Oct 13, 2011)

Coulomb said:


> Ok, that should do it  But 6:1 seems too short for decent top speed.


I'd be happy with 85-90mph top speed. I don't intend on using this for drag racing or anything. Just having a really freaking sweet vehicle. 



Coulomb said:


> Yes, sure. It's nice to have at all times, but the motor would quickly overheat. Note that 1000 A to two motors (2000 A from the pack) will demand a lot from the pack, too; it won't be able to supply this power for long.


Doesn't need to be for too long. Pretty flat area around here. Probably never really need max torque. (Because really, who needs 2800ft lbs of torque?)


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## major (Apr 4, 2008)

Bertzie said:


> I didn't do the math. This thing did. http://wahiduddin.net/calc/calc_speed_rpm.htm Engine speed of 3500rpm, transmission ratio 6:1, differential ratio 1:1, wheel size 32 inches. If you have different math, please share it.


I don't see an input for wheel size. Just "Loaded Tire Radius".


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## Bertzie (Oct 13, 2011)

Craaaaaaaaaaaaaaaaaaaaaaap! I thought that was diameter >.<

Now I gotta redo my maths.


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## Bertzie (Oct 13, 2011)

Okay, new maths. 3500rpm, 4:1 ratio, 32"diameter, (16" radius) speed would be 83.3, 

Would be 948ft lbs of torque per wheel, 1896ft lbs total. Still pretty respectable.


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## Anaerin (Feb 4, 2009)

Bertzie said:


> Okay, new maths. 3500rpm, 4:1 ratio, 32"diameter, (16" radius) speed would be 83.3,
> 
> Would be 948ft lbs of torque per wheel, 1896ft lbs total. Still pretty respectable.


I've got a tyre size to speed converter that actually uses the tyre code. 

http://evthoughts.blogspot.com/2009/05/testing-idea.html

So, using a "P175/35 R16" tyre, with 3500RPM motor rpm and a 4:1 reduction (4:1 at the differential, 1:1 to simulate direct-drive at the gearbox) get a total speed of 87kph or 54mph. It seems that, using those definitions, the tyres I picked are too small, but you get the idea.

For reference, the way I calculate the size is:

R16 is the rim diameter (in inches)
175 is the width of the tyre (in mm)
35 is the ratio of tyre width to thickness (in percent)

So, in this case, The wheel size (in meters) is:

(((16*25.4) + ((175 * (35/100)) * 2)) * 3.14159265) / 1000 = 1.661588352585

So the speed is: 

(((3500/4) * 60) / 1000) * 1.661588352585 = 87.2333885107125 Km/h


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## Bertzie (Oct 13, 2011)

The manufacturers website lists the tire size as this. 33x21.50R-15LT Gives a circumference of approximately 100.8"


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## Coulomb (Apr 22, 2009)

Bertzie said:


> The manufacturers website lists the tire size as this. 33x21.50R-15LT Gives a circumference of approximately 100.8"


You talk about a 32" wheel, which I assume is the rim diameter. That's huge, about twice most car wheel diameters.

With infinitely thin tires, that's 100.5" circumference. Are you also forgetting the tire width?

If they really are this large, then remember that you are reducing the force seen by the vehicle. It's like an extra 0.5:1 post-final diff ratio (making the overall effective ratio taller). So the 1900 ft.lbs of torque connected to a 32" wheel has the same force (and hence acceleration) as 950 ft.lbs with a 16" wheel. Larger wheels give you more speed and less torque than smaller wheels.


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## Bertzie (Oct 13, 2011)

Coulomb said:


> You talk about a 32" wheel, which I assume is the rim diameter. That's huge, about twice most car wheel diameters.
> 
> With infinitely thin tires, that's 100.5" circumference. Are you also forgetting the tire width?
> 
> If they really are this large, then remember that you are reducing the force seen by the vehicle. It's like an extra 0.5:1 post-final diff ratio (making the overall effective ratio taller). So the 1900 ft.lbs of torque connected to a 32" wheel has the same force (and hence acceleration) as 950 ft.lbs with a 16" wheel. Larger wheels give you more speed and less torque than smaller wheels.


 god no. That's 32" total tire diameter.


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## Anaerin (Feb 4, 2009)

Okay, so using "P546/41 R15" tyres (converted from 33x21.50R15 into metric using http://xepoch.com/mud/tire.cgi?h=33&wi=21.5&rr=15), I get a top speed of 137km/h (or 85mph)


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## Bertzie (Oct 13, 2011)

Still more than adequate for my driving needs.


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