Belt Pull Force Calculation
Belt Pull Force Calculation
(OP)
I'm trying to confirm what values I would use to calculate belt pull for a generator driven by a timing belt with a 2-stroke engine. The engine has a propeller on one end and the pulley for the generator on the other. All of the resources I have found for calculating belt pull use the full motor HP and torque values at a given rpm. I was told that I should only be using the torque required to overcome the magnetic and drag forces in the generator assembly to calculate the belt pull. Is this correct?
My goal with these calculations is to determine the correct bearing size in the generator for the load. The bearing life will be drastically different using the engine torque vs the generator torque, which is much less.
Thank you.
Casey
My goal with these calculations is to determine the correct bearing size in the generator for the load. The bearing life will be drastically different using the engine torque vs the generator torque, which is much less.
Thank you.
Casey





RE: Belt Pull Force Calculation
RE: Belt Pull Force Calculation
RE: Belt Pull Force Calculation
if the belt was driving the motor, or was the onl thing driven by the motor, then you'd use motor torque. but most of the motor torque is driving the propeller, yes? like the belt drives in your car, they're only transfering the power to drive the accessory, yes?
RE: Belt Pull Force Calculation
You are correct. Most of the torque would be driving the propeller. So for an accessory like a generator or alternator, the only power transmitted through the belt is the power required to turn the accessory?
RE: Belt Pull Force Calculation
RE: Belt Pull Force Calculation
RE: Belt Pull Force Calculation
RE: Belt Pull Force Calculation
RE: Belt Pull Force Calculation
RE: Belt Pull Force Calculation
This is not a safety-ractor that we apply, but a factor by which we multiply the force computed from power, speed and radius (F=P/2/pi/f/R in SI units) to estimate the actual force on the bearing while the machine is under load. Any safety factor we envision would be above and beyond this.
You can also calculate a static (Non-running) force from the belt tensioning procedure. If you apply a force F to move the belt a distance D perpendicular to the belt, then the static tension is
T = F * (CtoC/D)/4 where CtoC is sheave center to center distance. (simple geometry problem). Multiply this by 2 to get the force on the bearings in static condition in the static state immediately after tensioning.
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(2B)+(2B)' ?
RE: Belt Pull Force Calculation
But what about gunning the engine and accelerating the mass this propeller is working against? Certainly that would increase the load on the shaft and propeller sub assembly. So you would need to determine the belt size and performance against the maximum output of the engine, no?
So then the belt is sized against the engine, the propeller system is checked against such input torque performance.
That would be one way of looking at the problem. The system can only handle the maximum engine output, then add your safety factor to acknowledge worst case.
Regards,
Cockroach