Electric BMW 650cs Scarver

BMW 650cs Scarver

Another electric motorcycle conversion....
Late in 2012 I bought a damaged BMW 650cs Scarver very cheaply.
I sold the engine on eBay - actually I offered a partial refund on an exchange engine as I wanted the gearbox.
When the buyer dropped off his non-working engine (it had a holed piston) I removed and sold the clutch, starter motor and crank. I then set to work - surgery time! -I amputated the gearbox from the rest of the crank-case housing using a hacksaw, then a file. Butchery my pal calls it...

I figured retaining the original gearbox would solve a few things: The electric motor was too wide to allow me to position the motor shaft where it needed to be. Using the original gearbox gave me easy mounting as the bolt-holes were original of course - perfect pulley alignment and, oh yeah - some gears to play with. Note: no clutch needed.


I had learned a few things from my electric GPz:
Things to Avoid:
--- Lead acid batteries - lead is a heavy metal!
--- Chain drive - while efficient, can be messy, requires lube and is noisy
--- Tapping one battery for 12v - this unbalances the pack

Desired items:
--- NIMH or Lithium batteries - relatively light
--- Belt & pulley final drive - the Scarver is belt drive
--- A 72v to 12v DC-to-DC converter - share the load

One criticism you will see mentioned on the web is that with belt drive, you have to disassemble the swing-arm to change the belt - actually, that is not required with this bike (being designed with a single-sided swing-arm) it just slips right on. Well done BMW.

Components:
--- Controller: Alltrax 72 Volt 300 Amp (the Alltrax is rated at 72 volts but has a 90 volt cut-off limit.)
--- Gears: original 5-speed constant mesh gearbox
--- --- Gearbox Ratio's 2.750 / 1.750 / 1.310 / 1.050 / 0.840 : 1
--- --- Final Drive 2.94 : 1
I am going to need roughly a 2:1 reduction on the Motor to gearbox input shaft too...
If it was 1:1 then I'd expect these speeds:
1st Gear 51.71 MPH
2nd Gear 81.26 MPH
3rd Gear 108.55 MPH
4th Gear 135.43 MPH
5th Gear 169.29 MPH
But I just don't have the power for that - gearing too tall I am afraid.

With a 2:1 reduction in place I get the much more realistic:
1st Gear 25.85 MPH
2nd Gear 40.63 MPH
3rd Gear 54.27 MPH
4th Gear 67.71 MPH
5th Gear 84.64 MPH
That is what the calcs say, I'll see what reality has to say about this later!

--- Batteries: I have decided on 6 x 12 volt 40Ahr Yttrium LiFeYPO4 Batteries.
Giving me a modest 72v pack.
--- Capacity (Ah) 40
--- Max discharge current (A) 400
--- Optimal discharge current (A) 20
--- Max charging current (A) 40
--- Optimal charging current (A) 20
12v 40Ah
12v 40Ah Battery.

6 x 9kg batteries weigh 54 kg, being roughly 120lb.

--- --- I would actually prefer Aluminium/Air primary cells but they are not available yet.
--- Charger: LiPo/Lithium 72V/10A - 230V AC Input Charger. Charge voltage is 3.55V per cell. So is set at 81.65v
--- Motor: Advanced DC AC4-4002 6.7" 72 volt (Originally used on the Tropica)
--- --- Motor Spec:
--- --- Advanced DC AC4-4002 6.7" 72 volt
--- --- 10"x 6.7"
--- --- Series wound
--- --- 47 Lbs
--- --- 20 HP (Nom 6.5, peak 27)
--- --- should be kept below 5700-5800 RPM

To be continued...!
Bike left Side
Electric Scarver - Bike left Side.

Click the image to see a larger picture.