I have been intensively working on this since September. The bike is a Mongoose FS with the rear suspension tied down (wound the rear spring to limit travel and KEEP the motor drive chain on).
Using a 250 watt scooter motor,chain and sprocket to a jackshaft made out of a freewheel mx rear hub. From there, a bike sprocket welded on the other side of the jackshaft, driving a 42 tooth bike (standard?) chain ring adapted to a China girl rag joint.
Works OK, around 14 to one sprocket ratios and 13 mph speed with 24v batterys feeding it.
The following is WITHOUT the 24volt battery pack and instead uses an engine driving an alternator w/ a small 12v feeding the field circiut.
The alternator I am using is a Ford, external regulator style (NOT using the reg. at all). It has the power output directly connected to the scooter motor wires, with only a switch on the handlebar to shut it off and on.
Scooter motor speed is controlled by throttle position of the gas engine and the on/off switch. Later I will add a 2nd switch to the throttle control to kill big power at idle.
I am using a 12volt batt. to put current into the field circuit. Later, I want to add a snowmobile regulator (try to anyway) and a diode to charge the battery off the big output of the alt during use.
One of the tests I did was to remove the alternator and drive a 450w scooter motor as a generator. This did NOT work, the bike did move at a snail's pace, yes, it did generate current, but not much.
2weedwacker motors were tried. In a geared- down mode, one labored to just spin the alt. (probably a tired engine). The other, labored to spin both alt and drive motor with out load in direct drive - bike laying down- not ridden.
Here is what worked but the engine is too heavy for the rack mount- the HF 79cc is a sweetheart engine. With one to one ratio, spinning the alternator, I registered 50 volts at full engine rpm (3600).
This was enough to launch the bike with just a bit less inital thrust, than when it ran off batterys (not having the big reserve of amps), but still acceptably quick, and once getting up to speed, had to dial back to near idle to keep from overspeeding the scooter motor and maintain level speed (around 13-15 mph).
Having seen the alternator powering the bike, I swapped engines. To a 50cc Tehumseh snowthrower engine.(looking for light wt.)
This was a slug, it barely propelled the bike off idle and took forever at ful lthrottle to get up to speed. It is rated at 3 hp - maybe wound tight? But no torque.
The HF was a big block with a blower compared to the 50cc.
Winter is bearing down on the E-bike project. We have had an exceptionally warm November, allowing me to get farther than normal on this project.
I plan on pulling the 6 hp Techumseh off the 24 inch red bike and put it on the back of the Mongoose. Even with that 10 pound engine, the bike will weigh over 85 pounds, BUT total wt. won't be excessive because I weigh 135#. I think the 6hp will have enough torque to replicate the performance of the HF engine and it is ten pounds lighter.
I am out to ride with the same speeds and mode as a normal bike. I just don't want to deal with batterys and controllers. A Milk crate will cover the engine on the rack.
I will be New York legal (with this bike at least).
Hope the info is useful.
Using a 250 watt scooter motor,chain and sprocket to a jackshaft made out of a freewheel mx rear hub. From there, a bike sprocket welded on the other side of the jackshaft, driving a 42 tooth bike (standard?) chain ring adapted to a China girl rag joint.
Works OK, around 14 to one sprocket ratios and 13 mph speed with 24v batterys feeding it.
The following is WITHOUT the 24volt battery pack and instead uses an engine driving an alternator w/ a small 12v feeding the field circiut.
The alternator I am using is a Ford, external regulator style (NOT using the reg. at all). It has the power output directly connected to the scooter motor wires, with only a switch on the handlebar to shut it off and on.
Scooter motor speed is controlled by throttle position of the gas engine and the on/off switch. Later I will add a 2nd switch to the throttle control to kill big power at idle.
I am using a 12volt batt. to put current into the field circuit. Later, I want to add a snowmobile regulator (try to anyway) and a diode to charge the battery off the big output of the alt during use.
One of the tests I did was to remove the alternator and drive a 450w scooter motor as a generator. This did NOT work, the bike did move at a snail's pace, yes, it did generate current, but not much.
2weedwacker motors were tried. In a geared- down mode, one labored to just spin the alt. (probably a tired engine). The other, labored to spin both alt and drive motor with out load in direct drive - bike laying down- not ridden.
Here is what worked but the engine is too heavy for the rack mount- the HF 79cc is a sweetheart engine. With one to one ratio, spinning the alternator, I registered 50 volts at full engine rpm (3600).
This was enough to launch the bike with just a bit less inital thrust, than when it ran off batterys (not having the big reserve of amps), but still acceptably quick, and once getting up to speed, had to dial back to near idle to keep from overspeeding the scooter motor and maintain level speed (around 13-15 mph).
Having seen the alternator powering the bike, I swapped engines. To a 50cc Tehumseh snowthrower engine.(looking for light wt.)
This was a slug, it barely propelled the bike off idle and took forever at ful lthrottle to get up to speed. It is rated at 3 hp - maybe wound tight? But no torque.
The HF was a big block with a blower compared to the 50cc.
Winter is bearing down on the E-bike project. We have had an exceptionally warm November, allowing me to get farther than normal on this project.
I plan on pulling the 6 hp Techumseh off the 24 inch red bike and put it on the back of the Mongoose. Even with that 10 pound engine, the bike will weigh over 85 pounds, BUT total wt. won't be excessive because I weigh 135#. I think the 6hp will have enough torque to replicate the performance of the HF engine and it is ten pounds lighter.
I am out to ride with the same speeds and mode as a normal bike. I just don't want to deal with batterys and controllers. A Milk crate will cover the engine on the rack.
I will be New York legal (with this bike at least).
Hope the info is useful.
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I was a little confused about your tecumsehs. You list the 49 as 3.5 hp and the 98 as 6. Wondering where you got those numbers. My 49 is rated as 2 and the 98 is 3.5. Might explain the bogging under power. 
