# Any ideas for gearbox or other solution for direct drive motors?



## Daanii (Sep 3, 2009)

We are building a low-speed (maximum of 35 miles per hour) Ford Ranger conversion. We took out the rear axle and put in an independent rear suspension from a Ford Thunderbird. Then we got some custom-made half axles, each of which fits into a wheel on the outboard end and onto an electric motor shaft (7/8 inch, keyed) on the inboard end. 

We use two electric motors, one for each wheel. They are ME-0708 motors, which we run at 48 Volts. The motors are rated at 4.8 kilowatts continuous, and 15 kilowatts for one minute. We have no gearbox between the motor shafts and the wheels. 

To test, we took the Ford Ranger down to the bare chassis, with no cab or bed, and added about 600 pounds of lead-acid batteries, motors, and the like. Since we took out the engine, transmission, and differential, I think we now have about 2,000 pounds total, or less, even with the weight we added back in. 

In our test, the motors could get the chassis moving on level ground, but seemed to stall going up a slight incline. We did not have any current limit set on the controllers (we have an Alltrax AXE 4834 for each motor), and saw a wisp of smoke come from one of the motors before we could shut it off. 

With direct drive, I suspect we do not have enough torque, even with the two motors, for the weight. One option would be to put in a 5:1 gearbox for each motor, but I'm not sure we have enough space to fit it. Nor can I find anything really suitable. 

Any ideas? Is a gearbox the best solution? Could anything else be causing the problem, other than not enough torque?


----------



## Woodsmith (Jun 5, 2008)

I could suggest replacing the original axle back in the frame and using the gear reduction in that. Then use a single, much bigger, motor. You would probably still need to add a 2:1 or 3:1 reduction gear between the motor and gearbox.

I suspect that as you are running at such a low voltage the current will be high. Also as the motors are expected to run at wheel speed the low speed will also mean high current in the motor.

All this add up to a lot of heat in the motor as it is effectively running at, or near, stall.

My cargo trike is being designed to use a direct drive 11" fork lift motor with around a 6:1 reduction to a 25" diameter wheel. I am expecting high current like this but hoping the big motor will dissipate the heat with some forced air cooling.
I expect to keep the motor below 3500rpm. However, I could reduce the gearing even further and use a smaller, higher speed motor. But I don't have one to hand.
I plan to set up at 72v but to later run at 144v, or more.


----------



## Ivansgarage (Sep 3, 2011)

Daanii said:


> We are building a low-speed (maximum of 35 miles per hour) Ford Ranger conversion. We took out the rear axle and put in an independent rear suspension from a Ford Thunderbird. Then we got some custom-made half axles, each of which fits into a wheel on the outboard end and onto an electric motor shaft (7/8 inch, keyed) on the inboard end.
> 
> We use two electric motors, one for each wheel. They are ME-0708 motors, which we run at 48 Volts. The motors are rated at 4.8 kilowatts continuous, and 15 kilowatts for one minute. We have no gearbox between the motor shafts and the wheels.
> 
> ...


Here is some good reading on direct drive, mizlplixs roadster.
http://ivanbennett.com/forum/index.php?topic=6.0


----------



## Daanii (Sep 3, 2009)

Woodsmith said:


> I could suggest replacing the original axle back in the frame and using the gear reduction in that. Then use a single, much bigger, motor.


I should have mentioned that we _*need*_ to have a separate motor for each of the rear wheels. That's why we took the solid axle out. We need to figure out how to make the separate motors work.


----------



## Woodsmith (Jun 5, 2008)

Daanii said:


> I should have mentioned that we _*need*_ to have a separate motor for each of the rear wheels. That's why we took the solid axle out. We need to figure out how to make the separate motors work.


Why the *need*?

It means you need to double up on everything. A gearbox will take up space and add weight.

What you could do is to make up a pair of enclosed chain/belt drives that off sets the motors from the line of the drive shaft.
The drive could be designed fairly flat, in the vertical plane, and the two of them could be placed in the centre of the axle line with the motors outboard.

That gives you the longest drive shafts and also means the motors can be placed out of the way of each other giving more space to add forced cooling.


----------



## piotrsko (Dec 9, 2007)

FWIW: my ranger at 5900 lbs fighting trim uses about 25 hp through a 8.167:1 ratio to climb a 3 % hill at 25 mph. I have a 11.436:1 option that reduces current by about 20% for the same hill. Motor is rated at 75 lbft torque. YMMV.


----------



## major (Apr 4, 2008)

Daanii said:


> We use two electric motors, one for each wheel. They are ME-0708 motors, which we run at 48 Volts. The motors are rated at 4.8 kilowatts continuous, and 15 kilowatts for one minute. We have no gearbox between the motor shafts and the wheels.
> <snip>
> Any ideas? Is a gearbox the best solution? Could anything else be causing the problem, other than not enough torque?


Hi Daanii,

You should have seen this coming. The torque constant for that motor is 0.13Nm/A. You say you have no current limit set, so default is 400A, I think. So at current limit, each motor produces 52 Nm. That is 38 lb.ft. Two motors and 12 inch rolling radius gives you a force of 76 pounds pushing the truck. That would seem barely enough to overcome the friction and certainly insufficient to overcome a small pebble against a tire.

I am surprised those brushed PM motors got the vehicle moving at all. They won't last long. With that little of force, it will take quite a long time to accelerate even to a modest speed. That time will be spent with the motors at full current limit, 400A, and they'll start smokin' quickly as you've seen.

You've made two serious mistakes here in my opinion. First is the absence of gear reduction. Secondly, the use of those PM brushed motors. They (even 2 and probably even 4) will not be up to the task of a full size EV even at low performance expectations. 

Regards,

major


----------



## Daanii (Sep 3, 2009)

major said:


> You've made two serious mistakes here in my opinion. First is the absence of gear reduction. Secondly, the use of those PM brushed motors. They (even 2 and probably even 4) will not be up to the task of a full size EV even at low performance expectations.


Major, thanks for your comments. We definitely did make a mistake with this, and should have seen it coming. We took the Burt Rutan approach: try it out and fix what doesn't work. That approach has its drawbacks, and we will need to chalk this mistake up to experience. 

What we would like to do is get the car rolling with these motors. That will give us a working car to test all the other parts as well. But it sounds like even a 5 to 1 gear reduction would not work well. I guess we'll have to go back to the drawing board.


----------



## Daanii (Sep 3, 2009)

piotrsko said:


> FWIW: my ranger at 5900 lbs fighting trim uses about 25 hp through a 8.167:1 ratio to climb a 3 % hill at 25 mph. I have a 11.436:1 option that reduces current by about 20% for the same hill. Motor is rated at 75 lbft torque. YMMV.


Thanks for the information. That's very helpful.

EDITED TO ADD: Could I ask what motor you use?


----------



## Daanii (Sep 3, 2009)

Woodsmith said:


> Why the *need*?


That's a fair question. We are building a "proof-of-concept" car with seven functional modules. Each module will have a publicly defined function and publicly defined interfaces, but will be a "black box" to the other module designers. That is, what the module does is specified, but how it does it is not. 

To that end, we have designed each of our motor/wheel modules to be separate. Any mechanical connection between them would violate the design rules we put into place. We could change the design rules if we absolutely have to, so I guess it is a "want" instead of a "need." But we would like to get the car rolling with independent wheels. 

With this modular approach, we can assemble the seven modules in less than an hour, have a working car, and then disassemble it again in less than an hour. Any one module can be easily upgraded without affecting the other modules. 

Once we have this proof-of-concept car working, and have learned from our many mistakes, we will move on to build something closer to a prototype.


----------



## Woodsmith (Jun 5, 2008)

Ahhh, that clarifies things.

Now, you can either go all 'technical' and design/build epicyclic gearboxes in the hubs or axle frame for each motor to drive, or you can go 'basic' and rig up a simple chain/belt drive system as I had described above.

The basic set up would be more adaptable as you can change the ratio easily until you find something that works with your motors to allow them to move the vehicle.

Also it would allow you to change your motors to ones that will achieve the performance you were after. I guess that would be important as your 'black box' needs to perform to your desired parameters to allow the development of the other 'modules'.


----------



## Duncan (Dec 8, 2008)

Daanii said:


> We took the Burt Rutan approach: try it out and fix what doesn't work. .


As a fan of Bert Rutan's work I would emphatically deny that he EVER made something without at least a thought about actuality

He would never have tried something that a few moments thought would have revealed to be ludicrous


----------



## Daanii (Sep 3, 2009)

Duncan said:


> As a fan of Bert Rutan's work I would emphatically deny that he EVER made something without at least a thought about actuality
> 
> He would never have tried something that a few moments thought would have revealed to be ludicrous


I take your point, and it's a valid one. But we did not try something that a few moments' thought would have revealed to be ludicrous. We spent a lot of time on this, contacted the motor manufacturer, talked with other people, and came up with our design. 

As it turned out, it didn't work. In hindsight, we made a mistake that was stupid and will be difficult to fix. But we did, and are doing, the best we can, with the knowledge that we have. You can learn from books. But you learn more by doing. 

Though I may be wrong, I think that is Burt Rutan's philosophy. I don't know much about Burt Rutan, but I have read about him. Although not directly quoting him, the authors of the book A Perfect Mess interviewed Burt Rutan and summarized his philosophy as this:

"The way to build a better aircraft wasn't to sit around perfecting a design, it was to get something up in the air and see what happens, then try to fix whatever goes wrong."


----------



## major (Apr 4, 2008)

Daanii said:


> We...contacted the motor manufacturer...


Motenergy blessed using the motors without gear reduction 

Hey, not meaning to rag on you, if fact, I commend you for sharing on this board. You learn from your mistakes, but also allow other to learn as well. Thanks.


----------



## Brute Force (Aug 28, 2010)

Burt Rutan's philosophy works great if you have Burt Rutan's bank account.

Seriously though, this project was doomed before it began if you're not interested in reading relevant books on the subject before trying your ideas.


----------



## mizlplix (May 1, 2011)

If you have to make those motors work, then My vote is with Woody.

Put an inboard carrier bearing to hold the half-shafts and use a toothed belt drive for each. 

If cost is a problem, use chains for your "concept" vehicle and go with belts on the prototype. Those drives are scalable and will transmit huge HP and torque.

In reality those two small motors are just not up to the task. 



Miz


----------



## Daanii (Sep 3, 2009)

Brute Force said:


> Seriously though, this project was doomed before it began if you're not interested in reading relevant books on the subject before trying your ideas.


Any suggestions on relevant books? _Build Your Own Electric Vehicle_ by Seth Leitman and Bob Brant gets into the topic of required torque a little. But they do not talk about direct drive setups at all. I could not find anything like the clear analysis Major gave in his earlier post in this thread. Any book that discusses that kind of thing I would love to read. 

The motors' maker, Motenergy, steered me to a guy who built a nice conversion using two similar motors directly driving his conversion. He used 3:1 reduction, and recommended 4:1 reduction. That's the only person I found who has done something like this, or written about it.


----------



## Daanii (Sep 3, 2009)

mizlplix said:


> If you have to make those motors work, then My vote is with Woody.
> 
> Put an inboard carrier bearing to hold the half-shafts and use a toothed belt drive for each.
> 
> ...


We do want to make these motors work as one possible module. We will probably also get some bigger motors to use as another possible module. The idea is that we will be able to swap out the wheel/motor modules in 15 to 20 minutes. So if these two small motors are not up to a task, we can swap in bigger ones. That's the concept we are trying to prove. 

It does sound like some sprockets and a belt will be the way to go. Another person who shared his experience took that approach. I would prefer to find a gearbox, but have not had any luck finding anything suitable. If anyone has any suggestions, that would be very helpful.


----------



## Woodsmith (Jun 5, 2008)

If you are set on a gearbox then you may have to look at industrial suppliers to get exactly what you want.
http://ondrivesus.com/gearboxes.htm for example.
If you can specify the speed, torque and ratio then you can see what a supplier has in stock.
There would also be different keyed shaft input and output, both male and female.

An angle drive box, wormdrive, would allow for a compact motor set up but depending on ratio it may be non reversible. That might or might not be a problem for you at this stage.


----------



## Brute Force (Aug 28, 2010)

> _Build Your Own Electric Vehicle_ by Seth Leitman and Bob Brant gets into the topic of required torque a little.


Chapter 6 covers the topic pretty extensively. Gives formulas, describes concepts, provides examples. Very well presented, good resource when put to use.

The belt/pulley idea will work, but will be $$$. Problem is the availability of a suitable large diameter pulley. The motor pulley will be on off the shelf item for less than $100. The large diameter pulley will more than likely need to be custom made as the stock units I found were SOLID cast iron (ridiculously heavy).


----------



## Brute Force (Aug 28, 2010)

Your motors turn at 3360 rpm @ 48v unloaded. You want your vehicle to be able to go 35 mph. Using the formulas at the top of pg. 156, somewhere around 7:1 reduction would give you the best possible chance of hitting your target with these motors. Once you get over 4:1, practical issues of pulley diameter limit their usefulness, unless you use multiple stages.

Direct drive is just a single speed transmission. The tables on pages 157 and 156 are spot on for your application, you just pick one gear ratio and ignore the others. Or use the chart to pick a ratio you you think might suit your needs better.

Or you could also spend 15-20 minutes swapping out your small motor modules for the ones with large motors.

For what it's worth, the concept does work, you just haven't scaled it properly yet.


----------



## PStechPaul (May 1, 2012)

When I was looking into a similar system, I found some sources of planetary drives. I got a quote from this company for a reduction drive suitable for direct drive, but I think the price was in the thousand dollar range:
http://products.matexgears.com/view...rs-torque-range-301-11-478-in--lbs-?forward=1

You might look at these. They are planetary gears from an automatic transmission, but look like they might work, he has at least two, and the price is good:
http://www.ebay.com/itm/5-Pinion-Re...-Transmission-Planet-Gear-Gears-/170992950873

Or these, maybe, for $35 each:
http://www.ebay.com/itm/GM-700R4-4L60E-TRANSMISSION-REAR-PLANETARY-GEAR-2671-/350185541678

These might work, for $170 each. 7:1 reduction will translate 3600 RPM to 514 RPM which is 37 MPH with a 24" diameter tire. For a 2200 lb vehicle at 37 MPH up a 5% grade, the wheel torque will be about 163 lb-ft. So only 80 lb-ft per wheel, and 12 lb-ft for each motor. 
http://www.ebay.com/itm/Wittenstein...atio-7-1-Planetary-Gear-Reducer-/181089620351

I found the spec sheet (auf Deutsch) and it looks like these may handle 14 Nm torque and 4000 RPM, but I'm not sure:
http://www-alt.alphagetriebe.de/pdf/alpha_gk_05_lpd0712.pdf

You can use my http://enginuitysystems.com/EVCalculator.htm to simplify the calculations.


----------



## Woodsmith (Jun 5, 2008)

Brute Force said:


> The belt/pulley idea will work, but will be $$$. Problem is the availability of a suitable large diameter pulley. The motor pulley will be on off the shelf item for less than $100. The large diameter pulley will more than likely need to be custom made as the stock units I found were SOLID cast iron (ridiculously heavy).


Could use a two stage setup with two belts and four pulleys in each reduction box. That reduces the size needed for the large pulleys.
Large aluminium toothed belt pulleys are used on some motorbike rear wheels, that could be a good place to start for the parts.


----------



## Duncan (Dec 8, 2008)

Hi Guys
You are not talking about much torque here, how about simple V belts? light easily available, cheap


----------



## Woodsmith (Jun 5, 2008)

Duncan said:


> Hi Guys
> You are not talking about much torque here, how about simple V belts? light easily available, cheap


I think when Daanii finds out that there is still not enough torque the motor size will go up.


----------



## PStechPaul (May 1, 2012)

Woodsmith said:


> I think when Daanii finds out that there is still not enough torque the motor size will go up.


Actually the motors will provide about 9.5 lb-ft (13 Nm) each, and through an 8:1 reduction drive the total torque will be 162 lb-ft continuous. That's enough for a 2200 lb vehicle to go up a 5% grade at 31 MPH (50 k/h), using 13 HP (10kW), which is within the continuous rating of these motors.


----------



## subcooledheatpump (Mar 5, 2012)

Call me a skeptic, a critic, or a naysayer... but 9.5 ftlbs at the motor? really?

In a Ford ranger? Sure, it probably would work without any extra weight but are you really going to drive around just a frame without any body panels? Even if it is a concept car, just exactly what concept are you trying to prove? I get the idea of the modular powertrain, but I'm still not sure why you started so small


----------



## Daanii (Sep 3, 2009)

Thanks very much to everyone for all the ideas and information. I've got three or four approaches now to look into, and should be able to find something that will work well. Plus, I have learned a lot. Again, thanks. 

Let me also explain a little more about our project by responding to the last comment in this thread, which reads:



subcooledheatpump said:


> Call me a skeptic, a critic, or a naysayer... but 9.5 ftlbs at the motor? really?
> 
> In a Ford ranger? Sure, it probably would work without any extra weight but are you really going to drive around just a frame without any body panels? Even if it is a concept car, just exactly what concept are you trying to prove? I get the idea of the modular powertrain, but I'm still not sure why you started so small


Those are good points. Particularly this question: just exactly what concept are you trying to prove? 

We are trying to prove that an electric car can be designed, built and used with a modular architecture. That is, with largely independent "black box" functional modules connected together with carefully defined interfaces whose specifications are made public. 

There are no modular cars on the market today. It's too hard to make a gasoline car modular. Carmakers talk about modular cars, but they are talking about assemblies, not functional modules. 

Think about computers, for example. A desktop computer typically has, at a minimum, the following modules: 

case
power supply
processor
motherboard
memory
hard drive
optical drive
monitor
keyboard/mouse
operating system
application programs
With the desktop computer's modular architecture, you can buy different modules and connect them together with a minimum of fuss. Then you can upgrade modules separately to improve your computer. For example, I built a computer 10 years ago that I have upgraded over the years. It was a good computer 10 years ago, and it is a good computer today. But that's only because over the 10 years I have replaced every module except the case at least once. Now it's hard to call it the same computer. It's like the Ship of Theseus. 

Try to do that with a car. You can't. Cars are not made that way. We want to prove the concept that an electric car can be made that way. Our modular car has the following modules:

car operating system
driver control unit
motor controllers
wheel/motors
car body
car chassis
power supply
To prove the concept, we want to be able to assemble our car from the various modules in less than an hour, and then be able to disassemble it in another hour. To do that, it made sense to use some lower-power motors, to make the wheel/motor modules lighter and more compact. (Since we used the rear end from a Ford Thunderbird, we need to fit the motors and half axles in an odd spot where the differential used to be. That constraint does not come with the concept, it's just an implementation detail.) We don't need to prove the concept that bigger motors would give us better performance. So the small motors will work for us, as long as they work at some level of performance (which they don't now). 

It may not sound like a big difference, but I think an electric car with a modular architecture can change cars and change carmaking.


----------



## Daanii (Sep 3, 2009)

Brute Force said:


> For what it's worth, the concept does work, you just haven't scaled it properly yet.
> 
> View attachment 15778


Brute Force, the setup you showed in your picture looks great! Is that yours? Can you tell me more about how the motors are connected to the pulleys? Did you design and build the gearbox yourself, or buy it made?


----------



## PStechPaul (May 1, 2012)

That is a beautiful bit of engineering. It is just awesome to look at!


----------



## Brute Force (Aug 28, 2010)

Thanks for the compliments! One of these days it might actually be finished. 

The motor pulleys are COTS Gates Polychain GT pulleys with taper locks. The driven pulleys were custom fabricated by RCD Engineering. Gives me 4.11:1, which works well for my motors and my application. The motor pulley is 34 teeth, the smallest recommended radius for the belt. And the driven pulley is 140 teeth, the largest that can physically fit in the chassis. I spent countless hours designing it and $$$ getting parts fabricated. I'm satisfied with the results, but don't really recommend going this route if you have time or budget constraints. This was mostly a labor of love...


----------

