- Blog entry posted in 'Uncategorised', August 04, 2011.
After mulling the requirements and several ideas around in my head, I figured out a way that I could make it work.
The current plan is to build a rack to mount on the back of the bike, to which the motor will be attached. I decided to make the rear wheel pulley-driven, rather than chain-driven as I had originally thought. I will be using the V-pulleys from an old Volkswagen Beetle engine, with the smaller pulley on the motor shaft, and the larger welded directly to the rear wheel. Just in case you don't know what a VW engine looks like, here's a photo showing the pulleys that I will be using:
You can see in the photo the two pulleys right on the front of the engine. Those are the pulleys I plan to use. If this pulley arrangement does not produce enough torque, I will simply find a smaller pulley for the motor. Easy enough.
I still had a problem with moving pedals, though. If I had the pulley connected directly to the wheel with the sprockets on it, they would still spin. Before deciding what to do, I decided to test my motor, to see which way the shaft turned when the case was connected to ground and the power wire connected to positive. The motor shaft turned the wrong way for what I was planning anyway. Then I realized that if I welded the large pulley to the opposite side of the rear wheel from the sprocket stack, the motor would be turning the right way AND it would allow the "ratchet" mechanism to work. When the motor is spinning, the ratchet works and the pedals do not move. Perfect!
I had hoped to give a good sketch rendering of the entire layout, but I'm afraid I'm really bad at drawing. All I can give is this MS Paint silhouette drawing of my plan:
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I'll post it later with all the labels and everything. I hope this is sufficient for now :D
My next entry will describe the power and control system for the motorized bike.
ElectroMaster, August 04, 2011
Good location for the motor. The sketch is easily understandable. What is an acceptable speed that you are aiming for?
DerStrom8, August 04, 2011
I am hoping for between 5 and 20 miles per hour (8km/h to 32km/h). By law it must be under 20 mph, or else I'd have to register it. I'm glad you can understand the MS Paint rendering. I will explain all the little odds and ends on it as the blog progresses :D Thanks for the comment!
Resistanceisbutyl, August 05, 2011
Just a thought, it should be easy enough to add a small DIP switch governor to the motor speed controller, to limit the top end to a "certain" amount during testing/demonstration, if you see where I am going with this.
DerStrom8, August 05, 2011
[QUOTE=Resistanceisbutyl;bt444]Just a thought, it should be easy enough to add a small DIP switch governor to the motor speed controller, to limit the top end to a "certain" amount during testing/demonstration, if you see where I am going with this.[/QUOTE] I have decided not to use a PWM speed controller for this particular project. There were several reasons for this decision, and I will explain them in a future entry. Otherwise, I would certainly take it into consideration ;) I don't think anyone will be clocking me on a bicycle, anyway :D
alec_t, August 14, 2011
Interesting project. If you have problems with the pulley system there is another approach: direct drive from a ribbed roller on the motor shaft to the wheel tyre. That system was used on a motor ( 49cc IC engine) - assisted bicycle I had in my youth. The engine was mounted on a pivoted arm over the back wheel and the roller was forced down onto the tyre by a spring. It could be raised away from the tyre by a lever on the handlebars, via a cable; a simple but effective 'clutch '. Surprisingly, there was little extra tyre wear associated with this drive system, despite having to bump-start the engine by pedalling to ~ 5mph then engaging the 'clutch' !
DerStrom8, August 14, 2011
Thanks for the suggestion alec_t. I had thought briefly about direct drive, but I was not sure about it. I figured pulleys would be the best way, but If they don't work out, I'll certainly look into it. :)
Birdman Adam, August 15, 2011
The drawing helps me visualize! BTW - is there anything wrong with reversing the motor connections to suit your setup?
DerStrom8, August 15, 2011
[QUOTE=Birdman Adam;bt452]The drawing helps me visualize! BTW - is there anything wrong with reversing the motor connections to suit your setup?[/QUOTE] Actually, yes. Because the starter motor is from a car, the case is grounded. If I swapped connections, I would have to make my entire bike positive grounded, which I did not really want to do. However, it worked out perfectly this way--the motor turns the right way to spin a pulley opposite the sprockets on the rear wheel. =D I think that's what I will end up doing.
