# Using motorcycle transmission, a good thing?



## elevatorguy (Jul 26, 2007)

I am looking hard at a 1988 BMW R100RT to convert to electric. Would retaining the transmission be a good choice? I think my motor mounting would be easier than mating to the drive shaft as I can use a clutch center and make an adapter.
Anyone ever done a BMW bike? I either convert this or find a unknown rolling chassis.


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## frodus (Apr 12, 2008)

Not many people retain the transmission, but it all depends. Is it shaft driven with a fixed ratio? Is the transmission separate from the engine? In many cases they're built into the same housing. It's extra weight and volume that can be better used for battery space.

There's performance gains (better acceleration) but not much as far as speeed, as that's limited by HP of the motor.

What kind of motor are you thinking? Range? Top speed? Budget?


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## RIPPERTON (Jan 26, 2010)

careful with BM's
first figure out what happens if you remove the motor.
does the bike fall into 2 pieces ?
An 1100 that I looked at was too hard to convert because there was no frame left after you took the motor away and keeping the gearbox was impossible too.
you can convert earlier BM's that had full cradle frames.


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## RIPPERTON (Jan 26, 2010)

ok if its like this then it wont be too much trouble.
Im with Travis, the gearbox takes up too much room better spent on batteries or a bigger motor.
Just secure the front end of the drive shaft with a bearing and belt drive it.


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## Woodsmith (Jun 5, 2008)

elevatorguy said:


> I am looking hard at a 1988 BMW R100RT to convert to electric. Would retaining the transmission be a good choice? I think my motor mounting would be easier than mating to the drive shaft as I can use a clutch center and make an adapter.
> Anyone ever done a BMW bike? I either convert this or find a unknown rolling chassis.


Is it a single sided swing arm?

That could be rather difficult to not use the gearbox as the swing arm is pivoted from it. You could remove all the gears from inside it and cut away some of the housing so that the swing am is still attached to the frame via the remains of the box.

If you retain the whole transmission then the front of the trans would be a bit difficult to mate to a motor. The front of the trans housing extends further then the bolt face and so a shaped spacer would be needed.

Here is mine when I was trying to use it for a reverse trike.

With a 9" motor on top.









With a 9" motor in front.









With a 12" motor in front.









The insides of the box.

















I decided against using it in the end and switched to a Honda VFR750 swing single sided swing arm with an 11" motor.









And then I decided to make my own swing arm that pivots on the motor axis.


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## elevatorguy (Jul 26, 2007)

frodus said:


> Not many people retain the transmission, but it all depends. Is it shaft driven with a fixed ratio? Is the transmission separate from the engine? In many cases they're built into the same housing. It's extra weight and volume that can be better used for battery space.
> 
> There's performance gains (better acceleration) but not much as far as speeed, as that's limited by HP of the motor.
> 
> ...


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## frodus (Apr 12, 2008)

60HP is ~22.35kw. I realize this is peak. At 72V, that's 310A on the battery side (keep that in mind so you pick cells that can source over 310A). For 100miles and ~125wh/mile (high estimate but I always overdesign to avoid disapointment) for a bike like that, you're looking at a minimum of 10-12kWh of energy storage. at 72V, that's ~175Ah batteries. I think they sell 180Ah prismatic batteries.... but they're huge. I realize there's only 24 of them, but still, they're quite large for a motorcycle. Consider 96V or higher and use smaller batteries for higher voltage, lower current to get the same power. At 96V, the Ah requirement drops to 130Ah.

Lets say you use 180Ah prismatic, they're 240-265 online... 24 of those, $5760 just in batteries. Then add a decent motor and controller for at least $2k, a charger, contactor, cables, BMS (if you choose to use one, not getting into that argument with certain people on this forum), DC-DC... you're looking at ~10k for a medium performance vehicle (read that as "not 60hp") and that's all assuming you can fit 180Ah cells on the bike. 

You could use lithium polymer out of RC vehicles, but I'd really suggest a BMS that monitors temperature and voltage.... having that kind of power under you and not using a BMS is a risk that I for one, would not take.

100mile range is quite a tall order, even with a car that has room. Why do you NEED that range? Is this for longer trips or for commuting? Can you charge at work?

60hp peak is possible, but the prices go up for everything. 

Consider NOT using the transmission and use that extra space for the batteries. If you limit the space you have, it'll limit your range. There's only a couple, out of quite a few bikes that ever used a transmission. Sure the performance is better, but range, weight and complexity suffer.... as well as a little efficiency.


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## elevatorguy (Jul 26, 2007)

The empulse by brammo got 100miles so I thought why not? I did some math last night and understand my goals are too lofty, should have done my homework first . I want fun to ride, not an electric scooter, typical outing after work are 50-100+ miles on the ICE bikes so that is the number I chose.
The gearbox is not that big and would greatly simplify the coupling to the motor, has the speedo drive, and would be quiet (not a fan of the chain drive). It weighs 25 pounds and is about 8-10 inches deep.
I am looking at some other donors now as well, but the BMW is having some issues, has bags I could put batteries in, has new tires and I already own it.
Also have never seen one converted.
I am new to Lithium and was looking at http://elitepowersolutions.com/products/index.php because I really don't want to risk big money on my learning curve about batteries.
I wanted to get opinions on people that have built e motorcycles and avoid costly rework, I have done some conversions that worked well but all lead acid batteries.


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## frodus (Apr 12, 2008)

100 miles and 18-20grand  You can have fun, but you're going to pay for range/fuel up front rather than pay as you go, like with an ICE. It's possible, but If you can settle for a lower mileage to fit your budget, then it will be a fun project... the issue is, when you aim high and get the bare minimum, you might be disapointed. 

If you decide to go with Elite, I'm a reseller for their systems... so let me know.


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## elevatorguy (Jul 26, 2007)

frodus said:


> 100 miles and 18-20grand  You can have fun, but you're going to pay for range/fuel up front rather than pay as you go, like with an ICE. It's possible, but If you can settle for a lower mileage to fit your budget, then it will be a fun project... the issue is, when you aim high and get the bare minimum, you might be disapointed.
> 
> If you decide to go with Elite, I'm a reseller for their systems... so let me know.


If I was goind to spend 20k I would buy the Brammo  I can go with less range, that is why I am ditching my truck project, expense vs range.
I will go fun over range but will probably need 50 or so, looks like that number is easier to achieve with the bike.
I am just now getting back to EV projects after a lengthy break, things have changed some in hardware.
I will let you know on the battery systems, thanks for the heads up


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## MikeB (Jan 2, 2012)

I like how you think so far.
I have an 1992 R100 R in the garage I have been thinking of electrifing. I live 2 miles from work up a mean hill and gears are good for that. Lets say 20 miles max riden easy and quicker than stock for fun. Anybody have an idea of the most bang for the buck battery ? I can solder and machine stuff as necessary. 
Thanks,


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