I'm quite fond of all of the commercially available electric motocross options, but not enamored with the fact that most of them start at price levels of $7,000 and above. They're mostly aimed at obtaining a near 250cc level of performance, but for my daily use I won't be needing more than 50cc. I don't need to go above 35mph and I don't intend to launch myself over 15-foot jumps.
So for the past week I've been poking around at various options and determined that I can obtain the following for under $1,000.
Top Speed: 35mph
Range: 20-30 miles
Weight: 180-220 lb
Motor: 60v 1kw 1.8hp 3700rpm
Battery pack: 60v 20ah
Build Cost: <$1,000
Rough Design Concept
I intend to make it road-worthy, even though it will be operating within a DMV loophole that prevents it from needing a license plate or insurance. So it will include lights, turn signals, and horn, albeit custom-made ones.
It's finally above freezing for the first time in a month. A toasty 54F. It's so "warm" I was able to work the ice out of the garden hose.
Parts everywhere. The parts on the far right won't be needed (fuel tank, exhaust, muffler, engine brackets).
Frame is pretty filthy.
I can only get is so clean with dish soap, water, and a brush.
I'll have to clean it further by sand-blasting it. But for now it's clean enough to start cutting and welding.
After measuring the frame some more and shopping around for materials I decided to start the CAD work all over again. The first two designs were too cramped or involved fairly expensive materials.
This latest design will be easily made with less than $60 worth of steel (L-channel and 1" square tube) and some sheets of polycarbonate (which I buy as scrap). All while allowing for a wider range of sprocket sizes.
And it will only require me to cut out and replace the small downtube that held the engine and skid plate, rather than having to alter the main fork of the frame.
I've found a set of Dual Sport tires to replace the current knobby tires.
Front Rim: 1.4x19
Rear Rim: 1.6x16
Stock Front Tire: 70/100-19
Stock Rear Tire: 90/100-16
Replacement Front Tire: 2.75-19
Replacement Rear Tire: 3.00-16
It looks like my final gear ratio setup is determined. I will have to double check the diameter of the replacement tire before I order any sprockets though.
Max Motor Speed @ 60V: 3750 RPM
Motor to Trans: 1.7:1 (10t to 17t)
Trans to Wheel: 4:1 (12t to 48t)
Max speed: 35.5mph
I also ordered a ton of parts from TNC Scooters, and major components from eBay.
Money spent so far: $507
Haven't done much except measure the motor, then research/shop for sprockets and chain.
As I remembered correctly, permanent magnet motors are definitely not free-spinning when unpowered, so I had to do some thinking about how to add an overrunning clutch cheaply. I'm going to be buying a bike hub that I can cut apart to build my own.
Starting work on the battery rack and frame.
And I lathed some aluminum collimators for the high power headlight LEDs. The wide angle will be angled further downward than the narrow one.
Feb. 24th 2009
I've been really sick for the past week and a half.
Yesterday I cut the end off of the bike hub, lathed it down, and made a bushing to weld into the end of it. I then made an adapter to bolt onto the freewheel.
Once the hub end is welded to its bushing I can bolt the assembly together and the overrunning clutch will be done.