starter motors...

[mike5721947]

well im wanting to convert a starter motor for a metal 12 project (electric bike) and am wanting to figure out the rpm and torque of most starters are running at. im wondering mostly for trying to find sprokets to use for this i need to figure out the torque the motor will produce and the speed it can reach (SAFELY )

if i remember correctly the starter motor has to run at almost 10,000 rpm (to over come the gear reduction of the flywheel) to get the motor to turn over.
im thinking of using a GM starter as i can find one for a cheap price. but i can use any one as i can always go though the junkyards (get one from a ford powerstroke desiel )

[TheSilentChamber]

I cant help you out on specs, but I know every thing I'v seen like it (barstool racers) used gear reduction starters becaues they can run longer without overheating. Your typical starter is designed to run for a very short time. Most (all that I know of) GM starters are direct drive, not gear reduction. Your forien cars are the ones that use this type, honda and mitsubishi I know do on most all of there cars after the late 80's. Just an idea.

[mike5721947]

well the only thing im not liking about the reduction motors are the complexity, and the reduction in the speed. (the direct starters have to spin faster (and are normally powering larger engines)

but is there a way to modify the starter to run cooler? (heatsinks, air intakes, fans?

but if the reduction starter is what i need do you know of a part # or anything? (a specific vehicle that has a large one)

[curtis73]

Aside from parasitic losses, a gear reduction starter can just be geared back up without consequence. Many hi-torque V8 performance starters are capable of producing 150ft-lbs or more after a 4.4:1 reduction, so the motor itself should be capable of 35ft-lbs or so. Many of them are advertised around 1.5-1.9 hp.

I'm not sure if you could supply enough airflow to the starter motor since its a sealed unit, and a heatsink would only be partially effective. Also keep in mind that those above ratings are at about a 250-amp draw. That will drain a 50-lb car battery in less than a minute of going up hill. The starter motor itself (aside from overheating troubles) is designed to run in 30-second spurts with several minutes in between to recover. Running one continuously will cause internal wiring, connections, brushes, etc to just fry.

I think its feasible, but maybe with a less potent motor. Maybe one that's not designed for 3-second bursts at full power.

[mike5721947]

well im thinking of sidestepping a bit, but again i dont know the RPM or torque the motor would produce (5hp briggs motor)

im thinking of wedging this into a *massaged* bmx frame.


ok i admit it, its going to be alot more then massaged.

[mike5721947]

ok well i found some info for the briggs 3.5HP motors. the max RPM is 3300, and the torque # is 4.6FT/LBS

im 155LBS and the bikes probly going to be 100LBS about.

so what gearing should i need with 22" tires (20"bmx rim with tires)

i know i can get a 60T rear sprocket and a 15T clutch bell. (4:1 ratio)

but im thinking i need alot more torque.

(that electric motors looking mighty nice now) but it needs gearing help to (my calculations it needs 10:1