RFQ 2 ea. main bevel gear and matching pinion bevel gear - Page 3
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  1. #41
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    Quote Originally Posted by Milland View Post
    ...For the main gear, a tough, hard plastic like PEEK might work for you, ideally with a fill material like glass or carbon fiber (but you'd NEED hard metal pinions with a fill).

    StackPath

    Replacing Metal with PEEK Polymers to Improve Gear Reliability, Performance and Efficiency

    ...
    I'll check out PEEK polymers. I was thinking of making the main bevel gear out of glass-filled nylon, but don't know if/how it could be machined.

    The most popular propellers for alcohol/castor oil fuel model aircraft engines are made of glass-filled nylon by Master Airscrew but they're injection molded. Cost prohibitive until I win the lottery.

    Classic Series | Master Airscrew

  2. #42
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    Quote Originally Posted by saucerdesigner View Post
    I'm not an engineer either and very inexperienced at machining, obviously, and not sure I understand how a reduction gearbox would help in my case. The main gear diameter and RPM cannot be changed as the lift to be produced is predicated on those values. The main gear is a ring bevel gear supported by bearings at multiple points around the periphery.
    Thanks for the suggestions though.
    You missed the part about "lower tooth speed will help it live", so you doo the reduction in stages, not all at once, with a planetary gear, not all at the bevel.

    You really, really need to seek out a gear expert.

  3. #43
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    Quote Originally Posted by digger doug View Post
    snip - You really, really need to seek out a gear expert.
    Agreed. I'll seek out a gear expert before requesting a quote again. Suggestions on a gear expert are welcome.
    The main gear has to turn at 6K RPM (at full throttle). There is no option for further reduction. Are you suggesting I use the planetary reduction to reduce from 5 to 1 in stages (adds weight, complexity and losses)? Forgive me but I don't see how that will lower the tooth speed of the main bevel gear.
    Last edited by saucerdesigner; 04-16-2021 at 08:09 PM.

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    Quote Originally Posted by saucerdesigner View Post
    Agreed. I'll seek a gear expert out before requesting a quote again. Suggestions on a gear expert are welcome.
    The main gear has to turn at 6K RPM (at full throttle). There is no option for further reduction. Are you suggesting I use the planetary reduction to reduce from 5 to 1 in stages (adds weight, complexity and losses)? Forgive me but I don't see how that will lower the tooth speed of the main bevel gear.
    I think I'm with DD now, free advice on PM has sort of reached its limit.

    If you're set on a specific size and pitch of prop so you need that RPM at the blade, the idea of the staged reduction is so the surface speed at the final drive is reduced, with larger-section teeth to handle the loads and reduce deflection.

    So roughly a 2.5-1 reduction with the planetary box, then a 2-1 at the final drive to go from 30K to 6K. Remember, the worry expressed by others was about the surface speed of the meshing teeth, with a smaller main gear (from 12"+ to ~4") you cut that speed at the teeth, while still maintaining the desired 6K RPM.

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    Quote Originally Posted by Milland View Post
    with a smaller main gear (from 12"+ to ~4") you cut that speed at the teeth, while still maintaining the desired 6K RPM.
    Someone actually sells off-the-shelf ground tooth spiral bevels in 1:1, 2:1, and I think 3:1 ratios. Can't remember who but they are out there.

    You also need to know what the load is before you go off half-cocked choosing materials ?

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    Quote Originally Posted by EmanuelGoldstein View Post
    Someone actually sells off-the-shelf ground tooth spiral bevels in 1:1, 2:1, and I think 3:1 ratios. Can't remember who but they are out there.
    But, but, but - don't you want the non-repeating tooth mesh?

    You also need to know what the load is before you go off half-cocked choosing materials ?
    Last time I went off full-cocked, the ladies all fainted, the cattle got pregnant, and storks went on strike due to overwork.

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    Quote Originally Posted by saucerdesigner View Post
    Agreed. I'll seek a gear expert out before requesting a quote again. Suggestions on a gear expert are welcome.
    The main gear has to turn at 6K RPM (at full throttle). There is no option for further reduction. Are you suggesting I use the planetary reduction to reduce from 5 to 1 in stages (adds weight, complexity and losses)? Forgive me but I don't see how that will lower the tooth speed of the main bevel gear.
    Your still not understanding. It's not the speed of the teeth, it's the mesh, you know the "rolling action" that is from properly made gears. And bevel gears are compromise in that department, hence the speed limits.

    We can only devote so much to teaching you.

    There are many books on gear design.

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    Quote Originally Posted by Milland View Post
    But, but, but - don't you want the non-repeating tooth mesh?
    Not particularly. Especially not with ground, carburized teeth. Unless this thing weighs 3 lbs total, not a chance in hell his aluminum/delrin gearset will hold up.

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    If my math is correct the load on the main gear at design point is estimated at:
    hp:1.7
    torque [lb force-ft]:1.5
    power absorbed [Watt]:1282.4

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    Quote Originally Posted by Milland View Post
    I think I'm with DD now, free advice on PM has sort of reached its limit.

    If you're set on a specific size and pitch of prop so you need that RPM at the blade, the idea of the staged reduction is so the surface speed at the final drive is reduced, with larger-section teeth to handle the loads and reduce deflection.

    So roughly a 2.5-1 reduction with the planetary box, then a 2-1 at the final drive to go from 30K to 6K. Remember, the worry expressed by others was about the surface speed of the meshing teeth, with a smaller main gear (from 12"+ to ~4") you cut that speed at the teeth, while still maintaining the desired 6K RPM.
    Thank you for the explanation. So if I understand, since the main gear has to stay at 12"+, after the 2.5-1 reduction the mating pinion will be 6"+.
    Very much appreciated. Sorry to be such a pain.
    SD


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