I want to engineer some way to use a std string trimmer motor (4-cycle) to drive a bicycle chain and sprocket. The geared-down driven sprocket could either then drive a large prop for "air-power", or drive the rear wheel, like the 80 CC PK conversion kits do. I don't have a machine shop or lathe, just basic power and hand tools. for the driver sprocket, I would like to use a std. sprocket from a rear derailleur.
I can't so far think of a good/easy way to connect a derailleur sprocket to a string trimmer output shaft. The output shaft pretty much does not exist...that is the problem. There is just a square hole
into which the square end of the flex shaft fits. Probably it needs some sort of adapter that would
bolt onto the output end of the engine, containing a bearing, in which is a square-shaped "key-
stock" shaft (to engage the engine) which changes to round, and on the other side of the bearing has a short round shaft of the proper size to fit the ID of the derailleur sprocket. This involves some complicated machining. If someone could put such an adapter into production, one could probably sell quite a few. (maybe such a sprocket adapter has already been developed?) The nice thing about this is that my 4-cycle weed wacker has an integral centrifugal clutch, so there is no need for any manual clutch on handlebars. You release the throttle...clutch disengages. Probably all the string trimmers are like this.
String trimmers are designed to produce a high RPM at cutter head, but very little torque, so a gear reduction is needed.
Any ideas/thoughts?
I can't so far think of a good/easy way to connect a derailleur sprocket to a string trimmer output shaft. The output shaft pretty much does not exist...that is the problem. There is just a square hole
into which the square end of the flex shaft fits. Probably it needs some sort of adapter that would
bolt onto the output end of the engine, containing a bearing, in which is a square-shaped "key-
stock" shaft (to engage the engine) which changes to round, and on the other side of the bearing has a short round shaft of the proper size to fit the ID of the derailleur sprocket. This involves some complicated machining. If someone could put such an adapter into production, one could probably sell quite a few. (maybe such a sprocket adapter has already been developed?) The nice thing about this is that my 4-cycle weed wacker has an integral centrifugal clutch, so there is no need for any manual clutch on handlebars. You release the throttle...clutch disengages. Probably all the string trimmers are like this.
String trimmers are designed to produce a high RPM at cutter head, but very little torque, so a gear reduction is needed.
Any ideas/thoughts?