Gears vs. sprockets. What should I use?

[MachX]

Hello All,

I am designing a small Mil-spec power generation system and I wanted to ask opinions on which energy transfer drive I should use. I am currently calculating speed and torque reductions so I have not reached a final ratio yet. My design will most likely take low rpm and increase it to a higher rpm at the generator. I've been looking at using two aluminum gears mounted on bearings in a housing (gearbox) or very small sprockets with a stainless steel roller chain. Which system is more efficient? If I were to use the chain drive would the losses due to friction and mass normally be much higher? If the generator is mounted below the power source vertically, will the normal force on the side of the chain moving in the direction of gravity, cause the climbing side of the chain to become more weightless as far as work required to pull it upward? Any opinions appreciated.

 

[HowlerMonkey]

I wonder if you can tailor the diameter of the generator section to suit your rpm range rather than use any transmission.

 

[pantaz]

... I've been looking at using two aluminum gears mounted on bearings in a housing (gearbox) or very small sprockets with a stainless steel roller chain.

How much power are you generating, and for how long? I wouldn't expect a very favorable MTBF with aluminum gears/sprockets.

 

[Pkruse]

I've seen chains used to transmit as much as 700 HP at 900 rpm. The choice is often bases on space available. Also, higher speed applications tend to work better with gears.

 

[MachX]

@HowlerMonkey

I have thought about this, The generator I am looking to use might actually be very close to the output of the power source in rpm. I guess the other problem is how to mount it.

@pantaz

Not much at all, 12-15vdc - 1A. the goal is a system to charge any modern USB powered device.

@Pkruse

True, For this design I don't expect it would exceed 900rpm, but I am still trying to figure out the motor to know for sure. It might even be as low as 200rpm. In this case a chain might work and help with orientation. In another design I have uses a turbine at 30,000 rpm. For that one I will definitely need gears and maybe ceramic bearings.

If I were to use follower gears in a line, to space the generator farther away from my power source for mounting purposes, would this be less efficient than a chain? For example 3 gears in-between main and reduction to space power output shaft away from generator shaft. I think this might be too complicated for what its worth being that each gear needs its own shaft and bearings. I have thought about belts, but I kinda want to overbuild this thing just because...and the chain seems more Mil-SpeC, where rubber can dry rot.

 

[Pkruse]

I've seen belts transmit 600 HP at 3600 rpm. They make planetary gears to step down a turbine, sometimes in two or three stages. Any of these can be high efficiency. I've seen a turbine planetary with more than 99%. But that was a rather special design that took 15 years to develop.

 

[MachX]

I've seen belts transmit 600 HP at 3600 rpm. They make planetary gears to step down a turbine, sometimes in two or three stages. Any of these can be high efficiency. I've seen a turbine planetary with more than 99%. But that was a rather special design that took 15 years to develop.

Im hoping I can get the turbine to work with a 2 gear system. Although planetary gears are awesome, I doubt I could find any that small. The turbine I have is small and produces fairly low torque. The designer rated it 25W at 30,000 rpm. Hopefully with a gear reduction I can increase the torque output about 4 times and slow the rpm to meet generator speed. The only other thing is the bearings. It has standard bearings being exposed to steam, so I thought about getting fully ceramic bearings, however they are $160.00 for two 3/16" bearings which is painful! I guess I will keep designing and see where I get.

Thanks for input everyone

 

[pantaz]

... Although planetary gears are awesome, I doubt I could find any that small. ...

I found a nice planetary set inside an old cordless drill. Should be strong enough for at least a working prototype.

 

[MachX]

I found a nice planetary set inside an old cordless drill. Should be strong enough for at least a working prototype.

I diddint think of that. I will definitely look into it!

 

[RocketSci5KN]

I'd look into the gearing in some of the high torque RC servo's - you can operate them backwards to convert low speed to higher speeds...