Fat rear tired commuter/MTB with FD, jackshaft and Weedeater

Now that's interesting. What's the minimum roller diameter you can use? If I go to the trouble of vehicle approval here, I need to know that I can get a strimmer (weedeater) motor to give me most of it's power at a maximum 16mph. Above that speed, you run into much more regulation.
 
Small displacement direct drive FDs generally run something in the 1 to 1 1/8" size. These rollers in my experience are easy to break loose(spin) due to the power the engine applies directly. If I were going to build a really viable small cc FD, I would use a reduction(as in this thread) and run a large roller.
I just ran a 3" roller @2000 rpms on a 26" tire thru my calc. It indicates a top speed of 17mph. Simply reduce the engines rpms to get close to 2k rpms and you have it.
The bigger the roller(with in reason) the better.
 
These are numbers on my drive..

( I use that neat little app for calculating drive ratios to engine rpms/speed available in this forum.)

Ratio between the engine and roller pulleys : 3.2:1

Roller diameter : approx 2.9" which is an approximate measure rough as the roller is. It measures 3" if you wrap it with a tape measure and divide by pi.

I need to get an accurate speedometer so I can get some speed numbers, but it feels like the cruise is about 16~18 mph with engine in it's 'happy spot' torque and smoothness-wise.
 
The whole page was a great read! Thanks! Strangely the Lifan FD weighs about what the Anzani unit did in the low 20lb range. The advantage of the Anzani is the lower engine. The specs are right in line with what you are wanting to build LII.
Center the build around a 3" roller, its a very efficient size. I don't know what ccs your regs. will allow. 50cc would work well. Also the newer 4stroke weedies are a good choice if you are required to have engines in the 30cc range. If you can design the driven shaft to mimic an engines crankshaft ie an internally threaded 5/8 shaft. You can use the cheap and easy roller design which allows the less than a minute roller changes. This allows for experimentation to optimize ratios, speeds, and have rollers for different conditions. Only tools need for roller fabrication are hole saws, a drill bit for the shaft size, and a drill.(drill press is better).
 
Funny that I'm using a worn out holesaw for the roller on my bike's drive.

I rode my bike across a dewy grass field, I can say now that the drive will slip if encouraged with acceleration.

I'm guessing the engine is domestic. Although it's very high quality for a US made product if it is, very quiet mechanically and big sealed bearings on the nose of the output housing.
 
You must log in or register to reply here.
Back
Top