# High RPM Gearboxes



## flashburn (Jun 28, 2011)

So with Tesla and AC propulsion both ditching transmissions and going with single gearboxes and high RPM engines, I'm wondering how feasible this is for the hobbyist. Something that can run at 15k rpm without disintegrating for example.

Can we buy the same gearboxes they use? Is there a place to source a custom gearbox? Are they easy to DIY if you can draw up a plan and get time on a CNC mill?

Is it even necessary for good performance or is going with a bigger ratio going to give you similar performance?

Are they double helical gears?


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## Woodsmith (Jun 5, 2008)

That is a very open question. Depends on what motor you have, what pack and what vehicle.

How about a motor bike gearbox?


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## piotrsko (Dec 9, 2007)

gear boxes are available, if you look hard enough. 15 k rpm isn't a problem either: Pratt Pt-6 turbines used in GS configurations, possibly surplus.

15K IS a problem for a big high torque motor however.


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## flashburn (Jun 28, 2011)

piotrsko said:


> gear boxes are available, if you look hard enough. 15 k rpm isn't a problem either: Pratt Pt-6 turbines used in GS configurations, possibly surplus.
> 
> 15K IS a problem for a big high torque motor however.


Well, like I said tesla and AC propulsion seem to use motors that achieve high RPM. The roadster hits 14k rpm and the t-zero motor is 13k rpm right? They seem to me like they're able to produce decent torque.


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## major (Apr 4, 2008)

flashburn said:


> Can we buy the same gearboxes they use? Is there a place to source a custom gearbox? Are they easy to DIY if you can draw up a plan and get time on a CNC mill?


Hi flash,

I doubt you can buy the gearbox Tesla uses; unless you purchase a service replacement at the high price and even that may not be available except to authorized dealers. It is likely Tesla worked with and paid for the development and tooling for that box and it is proprietary.

Sure you can get a custom gearbox, just like Tesla. But you can't afford that 

I don't know where you think you can get a high speed motor and controller which would need such a gearbox anyway. But, here is my experience on the subject. I worked with a group who developed a high speed (12 kRPM) induction motor. We used a planetary first stage reduction. This was incorporated in the drive end head (DEH) of the motor and could be configured as a 2:1 or 3:1 reducer. This is called a close coupled gear head. After that, the shaft speed is 2 or 3 times lower and conventional gearboxes or pumps can be used. 

We had to design the DEH as the housing for the planet gear set and also the input and output shafts. This is not a trivial task, but could be done by a DIYer. Machining those parts can be done at many shops without excessive cost. We did not get into the actual gear design but rather used a planet set from a GM truck transmission. We worked with a transmission shop and modified that standard planet set for the higher speed in areas like bearings and lubrication.

I can't get into much detail about those projects, except to say that approach worked pretty well for us. That was grant funded or private contract research. So the cost wasn't coming from my pocket  It would not be cheap, but depending on your skills, possible.



> Is it even necessary for good performance or is going with a bigger ratio going to give you similar performance?


The motivation for us was to reduce the motor mass for the power requirements. Running the motor at a higher speed means less torque needed for that required power. And torque is the factor which pretty much defines the motor size (mass). Considering the motor and close coupled gear head, I think we saved about 40% compared to a motor without the gear. Please don't quote me on that figure; it was a while back 

Food for thought,

major


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## flashburn (Jun 28, 2011)

Thanks Maj.!



major said:


> Hi flash,
> 
> I don't know where you think you can get a high speed motor and controller which would need such a gearbox anyway.


Can I not buy AC propulsion's t-zero motor? It seems on their site you can.
I've seen a couple of motors intended for motorcycle use as well with high rpm capacity.



> The motivation for us was to reduce the motor mass for the power requirements. Running the motor at a higher speed means less torque needed for that required power. And torque is the factor which pretty much defines the motor size (mass). Considering the motor and close coupled gear head, I think we saved about 40% compared to a motor without the gear. Please don't quote me on that figure; it was a while back
> 
> Food for thought,
> 
> major


Right, so with teslas 8.127 reduction you are essentially multiplying your torque by 8 until your motor runs out of steam. Just like ICE's multiply their torque with their transmissions so the torque to the ground in first gear is much greater than torque at the engine.

Essentially, I would like to be able to consider a setup similar to tesla's and AC propulsion's for the exact same reasons that *they* decided to go that route. If doing this requires similar motors, gearboxes, controllers and batteries then I'd like to see if those are available.
Since I've already seen similar motors and batteries I was inquiring about similar single speed gearboxes.


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## WarpedOne (Jun 26, 2009)

Azure Dynamics sells AC motors that go up to 12 000 rpm. They also offer suitable reduction gearboxes with 12:1 or 10:1 ratios.

Link to PDF.


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## mizlplix (May 1, 2011)

The gears in your pic are called "herring bone" design. They were said to be the ultimate for slow speed and high torque......about 1901.

A decent high speed affordable gearbox that is efficient and not a power waster would be a Jericho. It is a spur cut, dog ring design.

The trick is the spur gearing. They do not load the gearset axially to keep them quiet. Also shifting with dog rings allows a no clutch shift. You shift with the pedal down. Just jamb it into the next gear for an up shift. Down shifting is a little harder. You have to blip the throttle when putting it into a lower gear.

If i had one, i would have put it in my latest project to try.

A used one goes for $3500 or so. Miz


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## major (Apr 4, 2008)

flashburn said:


> Can I not buy AC propulsion's t-zero motor?


I've heard you have to be institutionalized  That is part of a company or university, not an average joe to get their attention.


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## flashburn (Jun 28, 2011)

mizlplix said:


> The trick is the spur gearing. They do not load the gearset axially to keep them quiet. Also shifting with dog rings allows a no clutch shift. You shift with the pedal down. Just jamb it into the next gear for an up shift. Down shifting is a little harder. You have to blip the throttle when putting it into a lower gear.
> 
> If i had one, i would have put it in my latest project to try.
> 
> A used one goes for $3500 or so. Miz


Shifting? Where I'm going, we don't need shifting.

We talkin' bout single-gear gearboxes.


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