# Sprockets, gearing and motor



## soon2bEV (Mar 14, 2011)

Now that I am past the fear of spark I have a new dilemma. 
The motor is 48v, 1000w, rated for 3krpm and 26a. Battery pack is 
4 12v 50ah MK Gel. Sprocket on the motor is 11 tooth and drive is 21 tooth. roughly 2:1, right?
Tires are 26", highly inflated and weight with me on is about 500 lbs. 140 in batts, about 80 or 90 lbs or less bike weight, then me, 210-220 or so.
I can get the bike moving, motors making sound, but I am not getting up to a good enough speed and then I pop the 35a breaker.
I am pretty sure the current gearing is too steep for the motor. Anyone know of any places that sell custom sprockets? Will I be able to work it out or is my motor too small for all the weight?
I was thinking a 6 or 7 tooth on the motor and maybe 30 tooth on the drive if it fits. Any enlightenment would be of great service.
thank you


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## MalcolmB (Jun 10, 2008)

26" bicycle wheels will roughly give you 15-20 mph at 250 rpm, so your gearing is far too steep, as you suspected, and this is overloading your motor and tripping the breaker. Your motor should be up to the task but you really need a reduction ratio of 10:1 or higher, which may require a two-stage reduction.

Try taking a look at 219 kart sprockets and chain. They come in a wide selection of sizes, and the small pitch may allow you to get sufficient reduction in a single stage, if you have enough clearance for the driven sprocket.


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## soon2bEV (Mar 14, 2011)

Rookie mistake I'm sure.. Mistakes and failure are the beauty in learning, it was nice to hear the brrrrr of the motor wanting to work at least. 
I can flip the motor, cut a hole in the side of the box. The motor can hang over just out of the box to attach to a sprocket the non drive rear wheel and attach a 100 tooth sprocket to that wheel since it rolls freely from the drive wheel. 10 tooth drive motor to 100 tooth wheel drive #25 chain..
I couldn't find any small size sprockets in 219, all I could find was for go cart sizes. I need a 10mm double d cut inside diameter and finding something that will work on my Worksman rear axle is even less likely. They make Great bikes, super slow to get parts from though.

Let me know if you know of anyplace I can get sprockets like what I need.
I have been searching the web for sprockets for weeks now having the inkling the gearing was too steep, but I had to try.

the rear axle is 5/8" with a key notch.


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## MalcolmB (Jun 10, 2008)

Totally agree about mistakes being the root of all learning 

Sounds like it'll be easier sticking with the #25 chain. There are some small sprockets here you might find useful: http://www.electricscooterparts.com/sprockets.html#8mm


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## soon2bEV (Mar 14, 2011)

thank you. 
That's where I got the bike sprocket for my motor and breaker for the batt pack. Whats nice about their website is they have technical info on the parts they carry. Also, their close so I have had a quick shipping time, since their in the same state. I would've bought the motor and controller from them had I found them sooner. The motor came with a 10 tooth #25 sprocket to start, I thought I'd be cheeky and make it so I could just use what I had. You know how it is, patience, it's a constant practice. Not to mention the creativity involved when not following a kit or plan other than what I put together. Keeps the brain thinking
I'm going to see if their are any good mini bike kart places locally since I really need to see more than just measurements on a web page. I know a 100 tooth will be about 8.5" or so, but attaching it to the wheel, and the 3 bolt patten on the hub and only 1" clearance to play with between the hub and outer axle....
I'll let you know what I can work out.
Cheers
-Daniel


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## soon2bEV (Mar 14, 2011)

First thing, if anyone notices my inability to use the proper spelling for their, they're and there, I apologize. It bugs me too, but I just get going and the fingers don't always listen. 
So, I have a 96 tooth 5/8" ID sprocket on order. I could get smaller rims/tires for the bike. Here again Worksman bike parts take a while to get, still waiting for a sprocket I probably don't need anymore. I ordered it 3 weeks ago now.. Are there any companies that make rims that are hollow in the center like so many adult trikes have?
Or do you think I can get away with 10 tooth to 96 tooth, now being able to pedal with the new plan. I had to move the drive sprocket off the pedal path to the motor path.


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## soon2bEV (Mar 14, 2011)

Oh, also, I somehow had myself convinced I was running on 26" tires.. They are actually 24"...
will the smaller tires and 96 tooth drive gear be acceptable for the gearing ratio being closer to above 10:1
The radians math is difficult to do without a TI-88 at hand. I Used to have a couple, but too many house moves, they get broken
thanks
D


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## MalcolmB (Jun 10, 2008)

The smaller wheels mean you travel slower for a given rpm, so that makes your gearing easier. You should be just fine with the 10/96 sprockets you've ordered – they should give you a working setup which you can fine-tune if needed once you find out what hill-climbing ability and top speed they give you.


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