Quote:
Originally Posted by Don Rotolo
OK, that changes things a bit - I was thinking you had to overcome 400 oz-in of friction and THEN 350 oz-in of torque on top of that.
The motor you selected might work, but not at 2000 RPM. To start an engine of that type (at least, those that I worked with many moons ago) needed about 500-700 RPM to start, but (as you said) only for a second or three.
Looking at the photo, see how the motor gear is about 10 teeth, going to a bigger gear of about 40, which is stacked with another 10 tooth, going again to a 40? Just what you need.
For the $25 it'll cost to make it happen, I'd say try it.
If you can include some kind of clutch to disengage and engage the starter at will, you might consider a flywheel. A jet engine starter - thinking of it, a helicopter too - first spools up to speed with a flywheel, then uses the stored energy to turn the engine, effectively multiplying the torque considerably at the very first stage, where you need it the most. For this case, a 4 ounce 2" diameter flywheel on the fastest shaft will store considerable energy, almost enough to start the engine on its own. The motor will take a second or 2 to spin that baby up.
Don
|
Thanks for the reply Don.
The starter shaft has a one-way bearing on it, so it completely disengages from the nitro engine once it is started. If I have gears resting against it, it would just sit there idle.
As far as the gear ratio itself goes, how does that work out? The 10 to 40 connection makes a 4:1 ratio. Then with another 10 tooth gear on the same shaft as the 40 tooth gear, connecting to a 40 tooth gear, is another 4:1 ratio. So do you simply add those up and come up with an 8:1 as the final drive?
Also, what should I connect the last 40 tooth gear too (meaning, what size gear should be on the starter shaft)? Another 40 tooth gear so it makes it a 1:1 at that connection?
One other thing of note; the motor specified shows a stall amp of near 92 amps. That means I need a battery that can supply 92 amps burst discharge - or it will never reach the implied stall torque we have been using as a baseline?