So, since I was concerned about over revving this small motor, I was going to change the trans output sprocket and the rear sprocket, but I got to looking at it and I was able to rotate the trans 90 degrees, notch out the motor support, and just use the crank/sprocket assembly that came with the kit on the drive side. I just bolted the 44 tooth sprocket from the back wheel to the crank sprocket. It was challenging to come up with a decent adjustable idler pulley setup, but now its all set. I took it for a short test ride and I don't think I will have to worry about speed anymore! I'm still waiting on my new clutch before I really give it a test. On the original clutch, one of the pads came unglued from the shoe, so I drilled it and countersunk a screw in it, but if that screw were to come out, it would destroy the drum, so no more testing until the new clutch comes in...
My latest mod
- Thread starter VMaxer
- Start date
The sprockets to the rear wheel are just like regular(on the right) so I have 21 gears, I just took the crank sprocket from the kit and used it on the left. Then I bolted the 44 tooth sprocket from the rear wheel to it. I re-shaped the original pedal crank arm on the right, so its offset just like the left. I did have to tack-weld the pedal on the left to prevent it backing out, since now I have right hand threads on the left side of the bike. You do have to be pedaling once the engine is engaged, but I got my new clutch in and just tested it out and it works fine. As soon as you let off the throttle, the clutch disengages and you can coast to the stop sign or wherever you need to stop. There is much less resistance pedaling now without the motor, not sure why, I guess all the extra chain going to the rear sprocket before added alot? Anyway, so far I'm pretty happy with it and in high gear I run out of horsepower before redlining witch is what I wanted...once my tachometer arrives, I will post what rpm I'm at when I run out of HP...
Ok, the problem with this setup is that with the current drive ratio, it does not matter what gear I'm in, in order to maintain at least 3000 engine rpms, I've really got to pedal 116 rpms. This means I'm going to eat clutches. Rather than fabricate a crank freewheel, I'm going to run another chain, this will always be in the highest gearset for me to pedal, but the engine will vary from the 2 other crank sprockets and all but the last 2 smallest sprockets on the rear tire. I should've known this setup was too easy!!! Now, if I didn't care about pedaling, none of this would be a factor and it would work great, but for right now, I like the option of being able to pedal home if something goes wrong. Anyway, this is sure a fun project!!!
I’ve never seen anyone connect directly to their bike’s sprockets, and keep the pedals working.
I’ve always thought the engine would spin the pedals out of control.
Your gear ratio must be VERY high.
That’s probably why your layout works, sort of.
Can you share what your gear ratio is?
I’m also trying to run my engine through the bottom bracket, and keep the working pedals.
Like you said, it’s not easy.
I’ve always thought the engine would spin the pedals out of control.
Your gear ratio must be VERY high.
That’s probably why your layout works, sort of.
Can you share what your gear ratio is?
I’m also trying to run my engine through the bottom bracket, and keep the working pedals.
Like you said, it’s not easy.
So, when I first tested this bike with everything set up like you normally would (sprocket attached to rear wheel) I was redlining the engine an not getting much speed. That's when I counted teeth on the transmission and found out I had a gear reduction of 5.86:1. That means that with an output sprocket of 10 teeth and a rear wheel sprocket of 44, my total reduction was 25.77:1!!! Calculating that out, it works out to 7000 rpm for 21mph!!! I posted a thread about it and someone said I got a transmission more suited for use on a 2-stroke. Then, the clutch pads came unglued and while I was waiting for the new clutch, I just figured if I went straight to the crank, I could shift gears and get the rpm down.
I rigged up some foot pegs for it right now, because with the current gear ratio, at 3000 rpm I have to be pedaling at 116. I only pedal to get it up to speed to save the clutch, then I put my feet back on the foot pegs. I really need the tachometer to arrive so that I can test this out properly. If it works OK, I can reduce my gears all the way down to 46.86:1. That would mean pedaling at 85 rpm with the engine at 4000. This engine reaches max torque at 4500, so for cruising, that's what I'd like to stay at. As of right now, I wouldn't recommend this for anyone else. At redline (7000) those pedals are going to be going 270 rpm, my footpegs are located above the rear axle, well out of harms way, but still...
I rigged up some foot pegs for it right now, because with the current gear ratio, at 3000 rpm I have to be pedaling at 116. I only pedal to get it up to speed to save the clutch, then I put my feet back on the foot pegs. I really need the tachometer to arrive so that I can test this out properly. If it works OK, I can reduce my gears all the way down to 46.86:1. That would mean pedaling at 85 rpm with the engine at 4000. This engine reaches max torque at 4500, so for cruising, that's what I'd like to stay at. As of right now, I wouldn't recommend this for anyone else. At redline (7000) those pedals are going to be going 270 rpm, my footpegs are located above the rear axle, well out of harms way, but still...
Sidewinder Jerry
Well-Known Member
Let's start with first things first you don't have 21 gears to select from. What you have is 21 gearing combinations; several of these are redundant ratios. A 21 speed bike is a term used by people who don't understand cycling drive systems. What you actually have is a 3x7 drive system. The correct way to shift it is 1(1-4), 2(2-5), 3(4-7) for 12 non redundant ratios; this would be the shift pattern for human power. For a motorized assist going through the bicycle drive system, I suggest this shift pattern 1(1-3), 2(3-5), 3(5-7) for 9 non redundant ratios.
Since the rear wheel uses a freewheel instead of a cassette, at least get a cro-molly axle. Freewheel axles are prone to bending. My personal advice would be to get a cassette hub and a double walled rim for the rear wheel. You could incorporate the extra gear but personally don't recommend going below a 13t sprocket.
Using a techometer you can then select a gear where max throttle allows the bike to stay at max horsepower rpm. This way by being able to select the next higher or lower ratio you can stay at max horsepower rpm thus equaling max average speed. Think of it like this on a pedal only multi drive system if a gear is too easy or too hard to comfortably maintain a cadence (crank rpm) of 70-90 it means you're in the wrong gear.
I'm all for innovation and creativity. However pedals that spin while under engine power is an accident waiting to happen. This is why shift kits were created in the first place. A possible soulation would be to attach the crank arms to outside of left and right freewheels then connect inside of the freewheels to the botom bracket spindle. This way the engine can power the rear wheel without the pedals spinning.
By doing what I'm suggesting you won't have to put a right side crank arm on the left side.
Since the rear wheel uses a freewheel instead of a cassette, at least get a cro-molly axle. Freewheel axles are prone to bending. My personal advice would be to get a cassette hub and a double walled rim for the rear wheel. You could incorporate the extra gear but personally don't recommend going below a 13t sprocket.
Using a techometer you can then select a gear where max throttle allows the bike to stay at max horsepower rpm. This way by being able to select the next higher or lower ratio you can stay at max horsepower rpm thus equaling max average speed. Think of it like this on a pedal only multi drive system if a gear is too easy or too hard to comfortably maintain a cadence (crank rpm) of 70-90 it means you're in the wrong gear.
I'm all for innovation and creativity. However pedals that spin while under engine power is an accident waiting to happen. This is why shift kits were created in the first place. A possible soulation would be to attach the crank arms to outside of left and right freewheels then connect inside of the freewheels to the botom bracket spindle. This way the engine can power the rear wheel without the pedals spinning.
By doing what I'm suggesting you won't have to put a right side crank arm on the left side.
How do you plan to keep the crank arms 180 degrees apart from each other? If they're both on freewheels with nothing else connecting them, they'll be able to spin independently of each other and just flop around all willy-nilly, which is no good.
Sidewinder Jerry
Well-Known Member
Good point.
Seems the only logical solution is how a standard shift kit works where the spindle is only driven by human power. Staton Inc does make a double freewheel shift kit capable of putting 3 chainrings on it. Then all you'd need to do is jackshaft to the right side.
A 3x7 drive system will allow you to really widen the ratio range more so than a 1x7 drive system could.
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Although I'd only build a motorized bike with multi speeds, I don't like to shift often.
On my last bike, I found myself shifting three times.
Start off in 1st, shift to 3rd, then 5th and cruise in 7th(15:1 final drive).
I'm not into max hp in city traffic.
Even max torque is unnecessary in stop-and-go traffic.
It's too noticeable, high rpm on city streets.
If needed, downshift to the appropriate gear to accelerate or climb hills.
It's a pleasant ride at 30-35mph, not having to wind it up all the time.
To each his own.
Sidewinder Jerry
Well-Known Member
Although I'd only build a motorized bike with multi speeds, I don't like to shift often.
On my last bike, I found myself shifting three times.
Start off in 1st, shift to 3rd, then 5th and cruise in 7th(15:1 final drive).
I'm not into max hp in city traffic.
Even max torque is unnecessary in stop-and-go traffic.
It's too noticeable, high rpm on city streets.
If needed, downshift to the appropriate gear to accelerate or climb hills.
It's a pleasant ride at 30-35mph, not having to wind it up all the time.
To each his own.
I'm 250 lbs and have 30% grade hills to contend with. At my size and small cc engines (50cc or less) along with frequent steep hills my average speed is only around 18 mph. Yes I may hit 50+ down hill but when having to enter a 20%+ grade hill at a slow speed then my speed is only around 8 mph.
I don't really plan on using that many gears, just a low one to start out on to save the clutch and then an acceptable gear for cruising at 25-30...I'm just having fun with it for now, but I plan on fabricating a jackshaft for it sometime. Once I work out some of the bugs, I will use what I learn to build a better one on a bike with a steel frame. This bicycle has an aluminum frame and I'm not sure how well it will hold up. I've heard they develop cracks around the welds over time when you put a motor on them...
