Like many others I decided to quit waiting for a decent electric road bike at a reasonable price, so I built one out of a spare bike I bought off eBay for about $700. I based mine on a '82 Yamaha turbo because 1) I have the ICE version (hence the spare), 2) I like that it is fully faired so it looks 'normal' and 3) it's a shaft drive and one of my main goal was to make it as maintenance free as possible. Shaft drives weigh a lot more and are not as efficient as chain drives, but they are maintenance free. Here is a picture of the finished product. Like Stryker (who built the 72 volt version) I live close to work so distance was not an issue, but speed and performance were, as I have over 3 miles of a rather steep curvy road to go home on. One big thing to consider when doing this is the finished product. Like Stryker I am using AGM sealed lead-acid batteries because of convenience. But since I like the final product so much my goal has always been to upgrade it to some Li-Ion or Ni-MHyd batteries as soon as the become commercially available. It would shave 100 lbs off and give me twice the range, so it's an investment worth making.
Step 1: First, find a donor bike
I have an 1982 Yamaha Turbo. It looks like this. I also had a spare-parts bike (that I bought off eBay for ~$700). It was, for the most part, complete but in pieces.
I decided that I was probably not going to use the spare-parts bike for anything so I stripped it.
Step 2: Strip it and start finding spots for everything
This is what it looks like gutted. I placed the motor in first and located the controller (the electronic carb for the motor). I am using 12-volt, maintenance-free wheelchair batteries; less range but more charges (& maintenance free). I stuck one of the batteries where the original 12-volt battery would normally go.
It is an Advance DC 6.7" 72 volt DC motor (You can run a 72-volt DC motor at 96 volts, you just have to be careful in your rpm-ratio calculations not to over speed it!)
I used a Curtis 72 to 120 VDC, 300 amp Controller (36,000 watts of power available)
Step 3: Connecting the Motor to the Drive shaft
Since the 1982 Turbo is a shaft drive, I had to put a jackshaft and belt drive to turn the drive shaft already on the bike. You really should use a conventional chain-driven bike for conversion. The motor goes in sideways and the drive sprocket just goes right on the motor shaft; much easier (but I already had this bike). Since the drive-shaft to rear wheel was about 2.8:1 ration, I used a 2:1 ratio on the jack-shaft to get an overall ratio of ~6:1. This ratio will be good for mid range power and overall speed, but DC motors have such high-torque at the low end, it will be a bit overpowering for the drive shaft. I turned the controller down to min current and min acceleration.
The only "engineering" part is figuring out where to attach all of the brackets & supports for all of the other components; I used only existing holes on the frame already. It's strictly trial & error.
Step 4: Where to put those batteries!
4 of the 8 batteries went on the sides (replaced the mufflers). I hung them with Uni-Strut channels from where the old side-handles used to be). I'm starting off with the cheapest sealed AGMA lead-acid batteries I could buy. If I like the results I will upgrade them to some high-end lead-acid batteries. When the price is right I'll go NiMh or Li-Io.
Step 5: Putting on the DC/DC converter & Throttle
The rest of the batteries were put on some aluminum angles located above the motor. The DC/DC converter hangs on those angles too. (The DC/DC converter takes the 96 volts used for traction and converts it to 13 volts to run the lights & such. It is the '12 volt' battery for the bike). I just wired the output of the converter to the Main fuse on the fuse box.
The motorcycle's twist grip moves a 0 - 5000 ohm pot-box that tells the controller how fast you want to go & how hard you want to accelerate. It behaves just like a normal throttle.
Step 6: Where to hang the Charger
The charger is designed to be mounted on-board and runs on 110 volts AC (household current). You can get them to run on 220, (and it would charge in 3 hours instead of 6) but it makes it hard to find a place to plug in if you want to 'opportunity charge' at work (or at someone else's house!).
Step 7: Last step
The only other 'major' component is the Main Contactor. It's an electronic 'throw-switch' that connects all of that battery power to the Controller. It is key-switch activated and runs on 12 volts. (I wired it into the Ignition fuse.) I also have it wired in series with the kickstand switch so that after you turn the key-switch you can only drive away with the kickstand up.
Step 8: A snazzy paint job & we are done!
After the snazzy paint job I covered the two sets of saddlebag batteries with half of an ABS tub that Vicki & I found at Lowe's. (Improvising being the key word here!) I put an 'Emergency' Disconnect up on the fairing (just in case something shorted out). It's the bright red knob below the left handle bar grip. I also put a 'Charging Complete' light on the fairing under the throttle grip.
It took me about 2 months of spare time to put it together (and I live on a farm so there is not a lot of spare time available). (Who needs TV anyway? It's over rated!)
Anyhoo, here are the 'specs':
-70mph top speed
-15-20 miles range (I don't baby it at all, so I usually see 15 miles/charge)
-Single speed (including the wheels there are only 6 moving parts)
-Cost to charge: 15 cents
-Can out-accelerate most 4-cyl cars.
-Maintenance: Check the pressure or change the tires every few years.
-Fun Factor: Off the gage.