Gears vs. sprockets. What should I use?

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In summary, the conversation discusses the design of a small Mil-spec power generation system, with a focus on the energy transfer drive. The options considered are using two aluminum gears in a gearbox or small sprockets with a stainless steel roller chain. Other factors such as efficiency, power output, and mounting options are also mentioned. The use of planetary gears and RC servo gearing as alternatives are also suggested.
  • #1
MachX
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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.
 
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  • #2
I wonder if you can tailor the diameter of the generator section to suit your rpm range rather than use any transmission.
 
  • #3
MachX said:
... 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.
 
  • #4
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.
 
  • #5
@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.
 
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  • #6
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.
 
  • #7
Pkruse said:
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! :cry: I guess I will keep designing and see where I get.

Thanks for input everyone
 
  • #8
MachX said:
... 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.
 
  • #9
pantaz said:
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!
 
  • #10
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...
 

What is the difference between gears and sprockets?

Gears and sprockets are both mechanical devices used to transfer rotational motion from one axis to another. The main difference between them is their shape and function. Gears have teeth that mesh together and transfer motion in a parallel manner, while sprockets have teeth that mesh with a chain and transfer motion in a perpendicular manner.

Which is better for my application, gears or sprockets?

The answer to this question depends on your specific application and needs. Gears are better suited for high precision and heavy load applications, while sprockets are better for lighter loads and situations where a chain is needed for power transmission. It is important to consider factors such as speed, torque, and space constraints when deciding between gears and sprockets.

Do gears and sprockets have different efficiency levels?

Yes, gears and sprockets have different efficiency levels. Gears have a higher efficiency, typically around 98%, due to their smoother and more direct transfer of motion. Sprockets have an efficiency of around 95%, as some energy is lost due to the chain needing to bend around the teeth. However, this difference in efficiency may not be significant enough to impact your decision between gears and sprockets.

Are there any limitations to using gears or sprockets?

Both gears and sprockets have their own limitations. Gears may not be suitable for applications with large speed variations, as they require precision alignment to function properly. Sprockets may not be suitable for high precision applications, as the chain can stretch and wear over time. It is important to carefully consider your application and its requirements when choosing between gears and sprockets.

Can gears and sprockets be used together?

Yes, gears and sprockets can be used together in some cases. This is known as a gear and chain drive system, where gears and sprockets work together to transfer motion. However, this requires careful planning and matching of gear and sprocket sizes to ensure proper functionality and efficiency.

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