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Discussion Starter #1 (Edited)
Background: I'm building an EV system for a prototype vehicle designed for slow speed (no more than 20mph). Though I should note these vehicles weigh up to 3 tonne. I've started to put together a ~90V battery pack and will be using a Hyper 9 motor to power it with.

I've worked out to get these heavy vehicles to move up the inclines and at speed/acceleration we need I'm going to need a 8:1 gear ratio gearbox - obviously this is far higher than a usual car box so will need a custom solution.

I've tried to contact several gearbox manufacturers in the UK but no one seems interested. Would anyone know of a supplier or know of anyone who has had a custom gearbox made for an EV project?
 

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Would it be feasible to use a Leaf gearbox?
Another alternative is to put a 4WD gearbox with reduction in the transfer case in there. That'll give you 8:1
But your post could do with some details about what you're feeding the output of the gearbox into. 20mph is what you would expect for dumpers, wheel loaders and tractors. Are you removing an existing gearbox?
I'm planning an electric tractor, and considering how to get from a fast-spinning motor down to 1750 rpm which is nominal input to the tractor gearbox. So far my best ideas have been leaf motor direct to massey clutch, software limiting to 2250RPM, or using another gearbox. wonder if anyone has adapted a leaf motor to a different transaxle
 

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Discussion Starter #3 (Edited)
These prototype vehicles are made from the ground up so not adapting anything.

I have looked at the leaf box since it is so close to my ratio but my 8:1 calculation was with using a 3.74:1 diff, so the real ratio I need between motor output shaft and axle shaft is 29.92.

Using the leaf motor would mean having to change the packaging space I've been given which may be difficult. If I was to use one any idea if I need to give it power or feed it some communication signal to make it work?
 

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A Hyper9 at 90V is likely to feel pretty dissapointing. You'd be better off with a higher voltage pack if you at all can.
 

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Discussion Starter #5
I don't have the space to make a larger pack for higher voltage. I've had some figures from a UK supplier of Hyper 9s and worked out wheel torque values when run through my diff and a yet to be sourced gearbox - in theory it should work.

The two performance profiles I care about are 0-20mph within 10 seconds & 0-2mph on a 30 degree angle within 5 seconds. A 3 tonne vehicle with 0.8m diameter tyres requires ~6500Nm wheel torque, ~40kW power to do this. I think a hyper 9 is capable of this.
 

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I've tried to contact several gearbox manufacturers in the UK but no one seems interested. Would anyone know of a supplier or know of anyone who has had a custom gearbox made for an EV project?
Almost every automotive transmission manufacturer has done some EV gearboxes, even if some of them are only proposed products for which they have not yet found a buyer. The are typically transaxles, not just transmissions, because few vehicles designed as an EV (rather than converted from an engine-driven vehicle) use a separate reduction box and final drive - a mass-production car wouldn't.

The overall ratio of the single-speed transaxles in modern production EVs is routinely around 8:1 (that's almost exactly the Nissan Leaf ratio, for instance), but that's including the final drive. They are geared to allow 10,000+ rpm motors to drive the car up to 150 km/h; you're looking for a slower motor but driving a much slower vehicle.

The UK is probably the best source of specialty automotive gearboxes in the world (from racing suppliers) - if you can't get a single new gearbox from someone there, it's not going to be easier elsewhere. I suspect that part of the problem is that 8:1 is an extreme ratio for a single reduction stage.
 

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I don't have the space to make a larger pack for higher voltage.
Unless you have a fixed and large cell size, with no cells in parallel, you could likely build a higher-voltage pack of the same size... if you needed to. Pack mass and volume depend on energy capacity and power capability; configuration determines the balance between voltage and current within that.

The HyPer9 is actually intended for your application (low-speed industrial vehicles), as a modern replacement for traditional "forklift" motors, so it seems like a reasonable choice.
 

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Using the leaf motor would mean having to change the packaging space I've been given which may be difficult.
A typical production EV transaxle could be used as a transmission (connected to a separate final drive unit), by replacing the differential with a spool and using one output (which normally goes to one wheel) as the output to the final drive.

One challenge in doing this is that most designs are laid out like a typical transverse engine and transaxle: the motor is transverse, ahead of (or in a Tesla Model S or X, behind) the axle line, with the two stages of gearing and an intermediate shaft spanning the distance from motor shaft to axle shafts. If you turn that 90 degrees for a longitudinal motor and output, the motor centreline (shaft) is offset substantially (about 20 cm) to one side from the output. With conventional shaft rotations, and the motor/transmission ahead of the final drive, the motor ends up offset toward the left side of the vehicle.

The notable exceptions to this motor offset are the GM designs - Chevrolet Spark EV and Bolt - which have a hollow motor shaft with one axle output running through it, so the motor is right on the axle line. The Spark has a uselessly low reduction ratio, but the Bolt has an overall ratio (motor to axles) of 7.05:1. The Bolt motor is far more powerful than required (150 kW), but it might be suitable at reduced voltage (it can put out 360 Nm, up to a speed determined by available voltage). It might also be possible to adapt another motor (such as the HyPer9) to the Bolt transaxle, using it as a transmission by replacing the diff with a spool; however, the motor and transaxle casings are likely integrated (the motor case is one side of the gear case), making it impractical to remove the motor case and thus impractical to use the transaxle separately from the motor.
 

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For an obscure option, which is based on production parts which are presumably long out of production and thus unsuitable for a new commercial vehicle, there's the motor and transaxle of the Ford Ranger EV. This is a Siemens induction motor (like the many Azure Dynamics units), with a hollow shaft, bolted to a coaxial transaxle containing a two-stage planetary reduction gearbox and differential. As with other EV transaxles it would be used by locking out the differential with a spool, and using only the output which doesn't go through the motor (the vehicle's right hand side in the stock installation). I don't know the gear ratio, but to be suitable for the Ranger it must have been close to the desired 8:1. It could even be used with the motor, assuming you can find an aftermarket inverter matched to this particular Siemens motor.

If using this gearbox without the motor, one challenge would be that the first gear of the transmission section is actually integral with the motor shaft, so if used with a different motor a replacement for that gear would be needed, mounted to the desired motor's shaft.
 

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One last note...
There are single-ratio gearboxes intended to be mounted to the output of an electric motor and used to drive the rear axle of an electric truck. While this seems ideal, they always have a modest reduction ratio (about 2:1 or less) to be suitable for highway speed. An aftermarket example which is still available to be purchased in individual quantities by a consumer is the ev-TorqueBox; that one is even available packaged with various motors including the HyPer9.

Perhaps the makers of the ev-TorqueBox would consider a custom unit with a different ratio (I don't see the stock gear ratio listed in their current website, but it was less than 2:1), but they would presumable still be limited by the single planetary gearset design to a something less than the desired ratio.
 

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Discussion Starter #11
Unless you have a fixed and large cell size, with no cells in parallel, you could likely build a higher-voltage pack of the same size...
True I could put the 8 modules I am going to use in series to make a 350V pack but would a hyper 9 still operate at that voltage? Obviously I could get a 350V motor but this will be larger and heavier I think? Also surely I would need a beefier fuses/contactors/charger/controller which will take up more packaging space?

The main reason I am more inclined to a lower voltage solution is these prototype vehicles will be in a workshop environment and they are nervous about having high voltage systems on vehicles where employees may only have basic knowledge of EV electrical safety. The nominal voltage of the pack I plan to build is 87V which I can justify to my seniors. Initially they were pushing for a <50V system which was just impossible.
 

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Discussion Starter #12
Perhaps the makers of the ev-TorqueBox would consider a custom unit with a different ratio
thanks for this, I've had a look at their website and sent them an email maybe they'll be able to help out.


A typical production EV transaxle could be used as a transmission (connected to a separate final drive unit), by replacing the differential with a spool
Is just connecting one side of the differential not an option, it would HAVE to be replaced with a spool? I wouldn't really mind about having to mount he motor off centreline of the vehicle.

To be honest though the solution I come up with needs to reproduceable, if I use a production part it needs to be available from the manufacturer for years to come. Using gearboxes from the Leaf/Bolt/Spark may not be a good long term solution anyhow
 

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Is just connecting one side of the differential not an option, it would HAVE to be replaced with a spool? I wouldn't really mind about having to mount he motor off centreline of the vehicle.
If you don't change the internals, the side you don't connect to anything will spin freely and the side you did connect won't spin at all.
 

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Background: I'm building an EV system for a prototype vehicle designed for slow speed (no more than 20mph). Though I should note these vehicles weigh up to 3 tonne. I've started to put together a ~90V battery pack and will be using a Hyper 9 motor to power it with.

I've worked out to get these heavy vehicles to move up the inclines and at speed/acceleration we need I'm going to need a 8:1 gear ratio gearbox - obviously this is far higher than a usual car box so will need a custom solution.

I've tried to contact several gearbox manufacturers in the UK but no one seems interested. Would anyone know of a supplier or know of anyone who has had a custom gearbox made for an EV project?

You are starting from the wrong place

3 tons and 20 mph is Forklift and Baggage cart territory

Why faff about with parts that are intended for different problems

You want Forklift bits - or even a complete forklift chassis
 

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Is just connecting one side of the differential not an option, it would HAVE to be replaced with a spool? I wouldn't really mind about having to mount he motor off centreline of the vehicle.
It needs something done, because...
If you don't change the internals, the side you don't connect to anything will spin freely and the side you did connect won't spin at all.
The alternative to a spool is to weld the differential gears together, which is a common technique in classes of oval track racing where budgets are very low and/or spools are not permitted. I wouldn't plan on that as a production solution.
 

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Discussion Starter #17
You are starting from the wrong place

3 tons and 20 mph is Forklift and Baggage cart territory

Why faff about with parts that are intended for different problems

You want Forklift bits - or even a complete forklift chassis
Yeah but where can I get the parts from?My company needs to be able to buy the components reliably for the next couple of years so can't utilise whatever is being sold on eBay second hand at one given time. I tried to find a UK supplier a couple months ago but had no such luck finding any parties interested.
 

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Obvious suggestion that brian will find fault with: find a transmission that has a ratio you like, buy replacement shafts, bearings & gears, build a container that will hold all of that out of 1/2" aluminium. Easily within reach of a home hobbiest, using home tools. Need to be able to weld, however.

It's not rocket science, I would know.
 

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Obvious suggestion that brian will find fault with: find a transmission that has a ratio you like, buy replacement shafts, bearings & gears, build a container that will hold all of that out of 1/2" aluminium. Easily within reach of a home hobbiest, using home tools. Need to be able to weld, however.
My first reaction was "nope, I see no problem with that". :)

If you want to become your own gearbox manufacturer without the ability to machine gears, gearsets are available from various sources to upgrade OEM or aftermarket transmissions, and a straightforward layshaft design with (as remy_martian suggested) a substantial but feasible reduction at each of the two stages would work... as long as you can get enough reduction ratio for both stages. It can even be simple because all of the shifting hardware is omitted.
 
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