Making my own sprocket
Well, I've had some time lately to spend on my tadpole project. Electric tricycle, two wheels in front, pedal assist one man vehicle.
I've had it out on the street and got a couple of kilometers on it now. Still no brakes, but what the heck, I'm using the 'short out the motor' braking system, and it works fine at this initial stage of testing.
I haven't gotten it out of low gear yet, and it's giving me an estimated 20 to 25 kph. This is a guess based on my bicycle speedo and the rate at which the neighbor's houses go by kind of comparison. At any rate, I figure the rear sprocket should be about 1.5 times the diameter it is now. That will give me a lower low 'gear' ratio, and will allow me to get to about 40 kph in high gear, which is looking about right to me in terms of the power I have in the motor and the maximum speed I feel to be safe to go at in this contraption.
So here it is. I'm making a new sprocket from aluminum sheet, and I have a question regarding the radius or diameter of the gullets in the sprocket. I'm using bicycle chain which is 1/2 inch pitch, and the rollers on it are .304 average diameter, which is just under 5/16 inch. What might be the proper diameter to make these gullets? I plan to drill out a ring of holes in the al disc, then machine away the outer portion, leaving a bit more than half the holes' diameter on the disc. I will then shape the tips of the teeth as required for a good clean wrap of the chain around this sprocket. I guess I'll have to taper the teeth from each side a bit as well so the chain can engage well even if off-angle a small amount. The sprockets will be lined up perfectly, but I just want to allow for some mis-alignment by doing this.
Any suggestions? I could use a 5/16 drill bit for the ring of holes, and for this I would use a short drill bit so it stays on target. I could always grind a custom bit for the smaller diameter if that's what I should be drilling here. I will be using a jig on the mill to ensure equal spacing for the holes, and to get the root diameter just right. It's mainly the fit of the roller in each gullet I'm wondering about. Thanks for any advice or input on this. Or criticisms, if that's what I should be getting.
I probably could buy a suitable sprocket, but I'm not sure about getting it in aluminum, and I want to keep this as light as I can. I don't really want a steel disc 10 inches in diameter on my back wheel. I would rather make this myself anyway, and I'll get to use my homemade indexing jig. I'll also get to fit the sprocket very concentrically to the hub, since I will bore it to fit before I remove the blank from the jig. I also want to drill a series of decorative holes in this sprocket, and co-ordinate the bolt holes to my hub, so that's another reason for making it myself.
I'm getting pretty anxious to get this thing on the road with a proper speed control and brakes too. So far I've been using the 'touch the wire to the battery post and don't burn my fingers' method of getting a test drive or two in. Pics are coming-
I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-