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Old 08-14-2010, 04:26 PM   #21 (permalink)
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honestly chains are a PITA. On my FZR it seemed like every 1k~3k miles I had to re-wax it and then adjust the rear wheel to keep the tension just right. I swapped it for a bike w/ a driveshaft and love it.

Since you aren't shying away from machine work, and the chain setup isn't even started yet, my vote is for driveshaft. There are plenty of touring bikes you could snag one from.
With any luck you could stack the motors directly on, or use a few gears w/ solid mounting plate.

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Old 08-15-2010, 08:52 AM   #22 (permalink)
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Appreciate the vote of confidence but this is a budget conversion both in terms of money in time so i'll live with a chain. I do have an option on a bmw k75 for version 2 which is shaft drive

So I need a little advice on the sprockets. The bike's stock ratio is 2.87:1 with a 15 tooth on the engine and 43 tooth on the rear. So i've done some maths and came up with the following.
Wheel diameter : 600mm (approx)
so one turn = 1.885m
so for 1kph the wheel would turn at 8.83rpm

speed_________wheel rpm_______Motor rpm (2.87)_______Motor rpm (3.58)
50kph (30mph) = 441---------------1265-----------------------1578
100kph(60mph) = 883---------------2534-----------------------3161
145kph(90mph) = 1280--------------3673-----------------------4582

I can achieve a 3.58 ratio by keeping the stock rear sprocket and going to a 12 tooth on the motor. Bearing in mind its a twin motor setup I'm guessing i will have plenty of torque even with such a low ratio , still let the motor spin fast enough while holding them in the power band. Most bike conversion i've seen on the web have anything from 1:4 to 1:7 ratios but most are using agni or perm motors. Any advice much appreciated.
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Old 08-15-2010, 09:41 AM   #23 (permalink)
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One thing that I never understood about electric bike conversions... Why do people keep using big motors (in this case dual motors) instead of a gearbox?

In the fifties all bikes had the engine and gearbox separate, with a short, heavyduty chain between... Get one of those, bolt it to the right place in the frame and use a single one of those motors... With three or four gears available that single motor should be enough for some serious speed and strong enough for burnouts in first gear if you like... And while a screaming 4 pot ICE from a newer bike would rip that gearbox apart, I'm fairly sure it will handle that power without flinching...
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Old 08-15-2010, 11:11 AM   #24 (permalink)
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Well I happen to agree. Thing is that one of my aims for this project is to try out the dual motor system. If it works out great. If not i'll redesign. One option I am researching is a cvt from a snowmobile.
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Now, Cole, when you shift the gear and that little needle on the ammeter goes into the red and reads 2000 Amps, that's bad.
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Old 08-15-2010, 04:12 PM   #25 (permalink)
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sportbike gearboxes are built into the bottom end of the engine, to use it will involve a bit of work. They also are built for an engine with considerably less low-end torque and a slipper clutch. It might separate ok and all you'd have to make are some covers to hold the oil in, but IMO dumping the gears is one of my favorite advantages of going electric.

As far as the ratio question, my vote is for the higher one (3.58).

What helped me make this decision for the E30 was looking up the transmission gear ratios. It turned out that 4th gear was 1:1, so that helped me get a feel for how much torque I was dealing with comparing stock motor torque to electric motor specs. You most likely don't have torque data on those suckers, maybe the best best is to set the max rpm at the highest speed you'd ever have the balls to go on that bike and pick the ratio from there. If you pick something reasonable like 100mph you could probly get away with something ~5:1. If it turns out to be fast enough at a drag strip then you could always swap the sprocket out, chains are an advantage with this.
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Old 08-15-2010, 04:39 PM   #26 (permalink)
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Quote:
Originally Posted by Automcdonough View Post
sportbike gearboxes are built into the bottom end of the engine, to use it will involve a bit of work. They also are built for an engine with considerably less low-end torque and a slipper clutch. It might separate ok and all you'd have to make are some covers to hold the oil in, but IMO dumping the gears is one of my favorite advantages of going electric.

As far as the ratio question, my vote is for the higher one (3.58).

What helped me make this decision for the E30 was looking up the transmission gear ratios. It turned out that 4th gear was 1:1, so that helped me get a feel for how much torque I was dealing with comparing stock motor torque to electric motor specs. You most likely don't have torque data on those suckers, maybe the best best is to set the max rpm at the highest speed you'd ever have the balls to go on that bike and pick the ratio from there. If you pick something reasonable like 100mph you could probly get away with something ~5:1. If it turns out to be fast enough at a drag strip then you could always swap the sprocket out, chains are an advantage with this.
Why make it complicated using a gearbox that needs to have a housing built? Like I said there are plenty of gearboxes with separate housings, and jackbauer obviously have found yet another option...

Dumping the gears have definete advantages, agreed... But given a choice of a large heavy motor on a bike, or a smaller, lighter engine with a gearbox (that's likely to be heavy, but decidely less heavy than the larger or second motor) my choice is simple... Gearbox it is... On a car it's an entirely different matter...
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Old 08-15-2010, 05:11 PM   #27 (permalink)
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Yeh i'm gonna go for the 3.58. Firstly it sorta "feels" right to have the motors doing about 3krpm at 60mph and second it greatly simplifies (read cheap) sourcing sprockets and chain.
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Now, Cole, when you shift the gear and that little needle on the ammeter goes into the red and reads 2000 Amps, that's bad.
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Old 08-16-2010, 01:52 AM   #28 (permalink)
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Quote:
Originally Posted by jackbauer View Post
The bike's stock ratio is 2.87:1 with a 15 tooth on the engine and 43 tooth on the rear.
I can achieve a 3.58 ratio by keeping the stock rear sprocket and going to a 12 tooth on the motor.
A smaller front sprocket will make the chain rub on the swingarm - some bikes will have a piece of rubber on the front end of the swingarm to keep this from happening as the suspension works.
12 is tiny.

I'd rather go up some teeth on the rear, than going down more than 1 on the front.


Don't run a new chain over worn sprockets for very long - it'll wear out the chain faster.
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Old 08-16-2010, 01:58 AM   #29 (permalink)
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Quote:
Originally Posted by Tweety View Post
Why do people keep using big motors (in this case dual motors) instead of a gearbox?
Torque maybe ?
Having a gearbox means having a clutch, so the clutch must be capable of handling the high torque of the electric motor(s).
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Old 08-16-2010, 03:21 AM   #30 (permalink)
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Not sure i understand why a smaller drive sprocket would cause the chain to hit the arm. A larger one yes. Anyway I have an option on a 50t driven sprocket so i could use a 14t drive to get almost the same 3.58:1 ratio which is only one tooth less than stock:
Honda CBR600 FM-FT 1991-1996 50T Talon Rear Sprocket on eBay (end time 16-Aug-10 12:09:26 BST)

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Now, Cole, when you shift the gear and that little needle on the ammeter goes into the red and reads 2000 Amps, that's bad.
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