RFQ 2 ea. main bevel gear and matching pinion bevel gear

[saucerdesigner]

Folks please don't waste any more time on this. I have discovered lots of errors in the Main Gear file and it looks like I'll have to generate it again from scratch. I apologize for the inconvenience.
SD

 

[Peter from Holland]

Perhaps get the manufactorer involved in the design

Peter

 

[saucerdesigner]

Thank you Peter. I'll try to keep things stateside for now.
SD

 

[EmGo]

Folks please don't waste any more time on this. I have discovered lots of errors in the Main Gear file ....

Doesn't really matter for a quote. It's always going to be expensive because bevel machines take time to set up.

1) A couple hours to figure all your settings
2) Four hours to set up for roughing
3) Build a holding mandrel
4) Rough first part, check it, if wrong adjust
5) Rough the teeth
6) Change over to finishing, two hours
7) Finish teeth on first part, then check, preferably in a rolling tester
8) Adjust to get the contact where you want it
9) Finish teeth on the remaining parts

Have to do this for both pinion and gear. As you can see, there's some time involved. For this number of parts, profiling in a mill probably makes better sense.

Also, by milling you could just as easily do spiral or skew bevel. Plastic teeth really want to have a contact ratio over two and they also like a full radius in the root.

 

[Dan from Oakland]

11" dia Delrin gear running at 6K RPM? 30K pinion? lube is going to be? That's quite an RC model. Pretty straight forward for a straight bevel gear pair, but the pitch line velocity will be over 18000 ft/min! Did I miss something?

 

[Milland]

EG, any thoughts on the wear aspect of Al against Delrin in an application like this? Especially at the design speed...

I'd wonder if a larger, courser pitch propeller meant for lower speeds might not work better, allowing more robust, lower RPM gearing.

 

[johansen]

I forget where but i was reading about a 6:1 helical gear for a helocopter. 1 inch wide 6inch diameter on the plastic driven gear. Something like 6 or 10 horsepower load.

The aluminum pinion and the plastic gear were both profile adjusted to account for the difference in stiffness.

 

[EmGo]

EG, any thoughts on the wear aspect of Al against Delrin in an application like this?

Nah, at the designed 18,000 ft/min pitch line velocity the delrin will melt down in about 15.7 seconds. That should be just enough to get this thing far enough off the ground to do some real damage when gravity takes over

 

[Milland]

So we're basically at put a dang motor out there with the prop and forget about gearing...

 

[DDoug]

11" dia Delrin gear running at 6K RPM? 30K pinion? lube is going to be? That's quite an RC model. Pretty straight forward for a straight bevel gear pair, but the pitch line velocity will be over 18000 ft/min! Did I miss something?

I don't think the Hughes 269c 2 place chopper has that big of a ring gear....
Hughes TH-55 Osage - Wikipedia

 

[DDoug]

Matched pair.....
DP-14 Multi Mission UAS - DPI UAV Systems

Might be direct coupling the Turbine engine output shaft to the pinion.

 

[Milland]

Matched pair.....
DP-14 Multi Mission UAS - DPI UAV Systems

Might be direct coupling the Turbine engine output shaft to the pinion.

A quick look at the video still makes me think direct coupling is unlikely. The orientation of exhaust and casing looks to be at right angles to the props, and besides, no small turbine is going to run slow enough for direct drive unless you define that as having reduction gears integrated into the turbine casing.

 

[DDoug]

A quick look at the video still makes me think direct coupling is unlikely. The orientation of exhaust and casing looks to be at right angles to the props, and besides, no small turbine is going to run slow enough for direct drive unless you define that as having reduction gears integrated into the turbine casing.

NO, not THAT one, I am thinking the OP is trying to doo direct reduction in one shot.

 

[saucerdesigner]

I have corrected the main bevel gear screw-up and now the inside diameter is as it should be. The old files have been removed.
I really appreciate the comments, especially regarding concerns about Delrin in contact with aluminum rubbing, a material suggestion, a call-out for tooth surface roughness, a question about lube and the concern about pitch-circle velocities.
The motors to be used in this twin-motor device are those powering a single-motor 450 size RC heli turning at the same RPM but what I had not considered is that the gears in those are much smaller, hence much lower pitch-circle velocities. I'm learning. At any rate the files are now up on the repository in a different folder. This time I'll be sharing the files without the option for editing them enabled. It's very likely that I inadvertently nudged the objects myself in the creation of them. Soon I'll again invite you all to submit a quote and I'll share a link.
Regards,
SD

 

[EmGo]

I really appreciate the comments, especially regarding concerns about Delrin in contact with aluminum rubbing, a material suggestion, a call-out for tooth surface roughness, a question about lube and the concern about pitch-circle velocities.

Delrin on aluminum is no big thing, but what is kind of a big thing is the way plastic gears behave. That's a whole 'nother specialty, because the material is so flexible and doesn't act like steel.

I'd be concerned about these even if they were carburized 8620 prperly lubricated (very light synthetic oil sprayed at the outgoing side of the mesh ...) straight bevels just aren't that good for this kind of thing. Then transferring the design straight across to a material that has specific and different requirements ....

What's the transmitted load, by the way ? You need to know that to figure the contact stress on the teeth. That's kind of an important number.

Maybe just get the cheapest price you can because when the teeth melt and the thing falls out of the sky, at least you won't have spent as much.

 

[saucerdesigner]

For what it's worth (not much), I never like using aluminum in a "rubbing" application, and against even Delrin you'll get some wear on both parts from use.

If you must use Al, use a harder alloy like 7075-T6, and have a surface finish callout on the teeth that limits how rough they are.

A couple of questions:

1. If you had to choose, what material would you use?
2. What do you think about using 7075-T6 Al for both the pinion and main bevel gear?

Thanks
SD

 

[DDoug]

A couple of questions:

1. If you had to choose, what material would you use?
2. What do you think about using 7075-T6 Al for both the pinion and main bevel gear?

Thanks
SD

I worked with a specialist gear engineer.

See if you can hire one for a few hours.

 

[Milland]

A couple of questions:

1. If you had to choose, what material would you use?
2. What do you think about using 7075-T6 Al for both the pinion and main bevel gear?

Thanks
SD

I generally think of 7075 Al as being pretty good for static strength, but try not to use it where there's any direct rubbing going on, and certainly not Al on Al. For most applications, identical materials rubbing is the quickest way to wear and particle generation.

For what you're doing, if we take cost out of the equation I'd be thinking something like hardened 440C or 17-4 H900 stainless for the pinion, with as close to a polished tooth face as I could get.

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

What occurred to me after thinking about your setup (but without checking the drawings, because reasons) is you need a stable relationship between the mating gear teeth, and as you apply load to them the teeth want to separate due to wedging forces.

So you need good brackets to support the gears and keep them in proper mesh, and a stiff material (like a reinforced plastic or a metal) for the large gear.

Not that it's ideal, but in some circumstances I could even see using the periphery of a ball bearing or two on the opposite side of the main gear to keep it from flexing away, or have the gear hub designed as stiff as possible (deep ribs), but that takes space and adds weight.

[Disclaimer - I am not an engineer, but am a reasonably accomplished mechanical designer with four patents and stuff I've made in space]

 

[Milland]

Another thought - you should forget the large gear set, and go find a suitable planetary reduction gearbox you can mate to the end of your motor, then use a much smaller volume gear set at the final drive of about 12 to 23 (or some other -1T ratio). Scale them up a little for the extra torque, you'll still be lighter and smaller volume overall.

You might be able to source the planetary box from an appropriate power hand tool, like a drill or similar.

The smaller final drive will be vastly more stiff and stable, the lower tooth speed will help it live, and it'll be much cheaper to make. Even if you have to have a planetary box made for your purpose, I still think you'll come out ahead from a cost and reliability standpoint.

 

[saucerdesigner]

Another thought - you should forget the large gear set, and go find a suitable planetary reduction gearbox you can mate to the end of your motor, then use a much smaller volume gear set at the final drive of about 12 to 23 (or some other -1T ratio). Scale them up a little for the extra torque, you'll still be lighter and smaller volume overall.

You might be able to source the planetary box from an appropriate power hand tool, like a drill or similar.

The smaller final drive will be vastly more stiff and stable, the lower tooth speed will help it live, and it'll be much cheaper to make. Even if you have to have a planetary box made for your purpose, I still think you'll come out ahead from a cost and reliability standpoint.

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.