Gear drives and design

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dog

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Dec 29, 2019
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I was in a shop,biggest gear you ever saw,buying some tooling,guy was yarning and digging stuff out for me,in comes a dude who wants a gear made,had the broken one from his jeep,machinist says" ok put it there buy the door,Ill do it" try to get back to yarning,etc,buddy pipes up with,CAN you do it,again,leave it by the door,
this happens again,Machinest exasperated turns and says"Ive fu%$3d up better jobs than that",went outside he had a lathe that the head
and tail stocks were house sized castings,8 foot chuck,trucked from NY state,was used turning shafts in hydro turbines.
I hope to get good at ordering gears,hats off to anyone chipping them out by the each.
 

Kiwi303

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En Zed. Aka The Shire.
Things to know about hardening and its effects upon gears:
  • All hardening can change shape of part from before hardening;
Billski
Normalising helps here. a big part of warpage is stress in the blanks from manufacturing processes, heat treating crankshafts for example, if not normalised forged cranks can go all banana-y, because the metal was squeezed from one shape to another and it REALLY wants to go back to how it was. Heating to a certain temperature (different for every alloy/item/process) and holding it there for a significant period allows the stresses to relieve themselves, and quenching/hardening would not cause the same degree of change of shape as un-normalised steels.

The other reason off the top of my head for post treatment finishing grinds is oxidisation, If the heating isn't being done in molten salt baths or in an oxygen free environment but rather in small scale open air systems, oxygen diffuses into steel, this reacts with the carbon in a very thin layer close to the surface and outgasses from the hot steel as CO or CO2, reducing the surface strength. This is generally negligible, but in very high tolerance systems, does need to be accounted for.
 

Pale Bear

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Sort of off topic .. I used to work for a place that had to have parts made of 62 - 64 hardness, I believe. They had a 2 part process of grinding those parts. On the O.D.s, .. the 1st grinding pass, on a new/rough hardend part, which was the 2nd dressing of the grinding wheel. And then, redress the grinding wheel, and do the 2nd/final pass on that same part. Back & forth ..

Maintaining the grinding wheel's dress, was huge. I didn't do the main grinds, (on the O.D.s) .. but, I was tasked to grind the ends of those parts, later .. and then, lap them. Those grinding wheels would load up, fairly fast .. and, then you were forced to redress it, fairly often .. if not, you'd just burn the parts, instead grinding them. But no matter what, .. very light passes, .. and you would get there, eventually.

Looking back .. the outcome was pretty impressive. Very smooth finish .. and within .0005".
 

Vigilant1

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I think I understand why belt PSRUs are more popular than gears for the amateur PSRU designer.

1) The perception that the belt will "take care of" the TV issues, so thorough analysis isn't required to get good results. This is the wrong reason to go with belts.
2) The perception that the analysis is required with both approaches, but "I can make my expensive mistakes faster and easier with belts." This seems likely to be true.
 
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PMD

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Apr 11, 2015
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Martensville SK
I am a spectator, not an expert in this topic. BUT: I can tell you that the gearing (and much shafting - literally not figuratively) for most funny cars and top fuel cars REGARDLESS OF THE NAME ON THE BOX comes from one place. So does (or at least did when I was last there) all of the gearing for Bombardier aircraft. I did a project with them decades ago, and as Billski said...a very deep and convoluted rabbit hole indeed!!!!

Similar to the black art of making very high performance gearing (that takes a lot of very proprietary knowledge to get dead on....and I strongly suspect Mr. Marcotte to be a member of that extremely elite club, the business of torsional resonance is not far behind. Yes, there is a lot of science and engineering calculations involved, but I have watched a 100 year old, very high profile automotive engineering company put their first airplane propeller on a drive train - and then go out and hire someone who had a huge track record at turning all of that science and engineering into something they did not have - a viable drive damper.

Don't get me wrong: I am one of the most vociferous proponents of backyard engineering, but when it comes to re-drives it is a combination of two very specialized disciplines that take decades of experience and credibility to even GET that experience that just doesn't fit into a DIYers time and resource frame very well. If you can find a drive with a track record such as what Ross has shown just go with it and be happy. Lots of other dragons to slay in the sky.
 

Lendo

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rv7charlie, stay positive while you can, for myself at 73 I'm looking forward to Blessed Relief :).
George
 

rv7charlie

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Pocahontas MS
Hey, I just turned 70 a few months ago. I'm cutting the flap pushrod holes on the RV7 fuselage today (it'll fly 'Tuesday') and watching for a project-something C182 or bigger to stick an LS motor in when the -7 flies. I intend to die in my sleep at 132 after flying a bit of acro in the afternoon. ;-)

I do have genes on my side; both my parents made it to 101, in pretty good health.
 

Lendo

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Vigiliant1. I checked with my Engineering friend in the States and he confirmed a single gear (one on one) would have HP efficiency of 90+%. That's where I got my 10% from. I can only assume 3 gears would be worse. I mentioned your heat calculations and he suggested that's why they need to have good lubrication and cooling.

PMD, I agree with your comments about Marcotte, I hadn't see the internals of his drive before, very professional indeed. Heat expansion between an internal Spur gear and Ring gear is minimal as they both expand outwardly and less heat expansion tolerance is needed.

I also noticed there was no end support for the Spur Gear (as the Powersport design has) so a lot of good design work went into that. I'm sure we would have heard about any problem in that regard by now if there were any issues.

I was surprised at the Damper as it's very similar to my Suzuki 1800 cc Motorbike Rear Wheel Drive Damper, not overly sophisticated but handled the big
V- twin drive-line.
George
 

Vigilant1

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Vigiliant1. I checked with my Engineering friend in the States and he confirmed a single gear (one on one) would have HP efficiency of 90+%. That's where I got my 10% from. I can only assume 3 gears would be worse. I mentioned your heat calculations and he suggested that's why they need to have good lubrication and cooling.
George,
Thanks. My original comment was here. I'm sure your friend knows his stuff, but I still suspect there's a misunderstanding somewhere. In a competently designed gear system, the losses per "mesh" would be closer to 1-2% than 10%.
Here's a fairly recent post from billski on a related issue.
Drivetrain Power Loss

Mark
 

TFF

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My old CBR600F2 engine supposedly made 100 hp but at the rear wheel 82 came out. More gears for sure. Now the gear finish is probably better today, but Honda is usually not the worst out there.
 

Vigilant1

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My old CBR600F2 engine supposedly made 100 hp but at the rear wheel 82 came out. More gears for sure. Now the gear finish is probably better today, but Honda is usually not the worst out there.
Lots of ways that could happen, including slippage between the tires and the steel dyno wheels. There's no way that 18hp of losses (13,000+ watts of heat) occured in the transmission. The gearbox would be red hot after even a "regular" ride at highway horsepower if anything like 18% of the mechanical output were being lost in the transmission gear set. More here in a similar vein in another thread, from billski. Drivetrain Power Loss
 

Heliano

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Campinas, SP, Brazil
Impressive. This topic is high quality course on geared systems! Two quick comments (I am a compulsive commenter): 1 - For aeronautical use, AGMA quality number 10 or 11 is advisable. To reach that level of quality, I believe (please, those with more experience correct me if I am wrong) that some post-heat treatment grinding is unavoidable. 2 - Three gear systems (as in the Viking engines) have a complicating factor: the middle (idle) gear is subject to much higher cyclic loads in that the load the teeth get from the drive side is reversed on the propeller side, therefore if something is going to break due to fatigue, it is probably the middle gear.
 

dog

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Impressive. This topic is high quality course on geared systems! Two quick comments (I am a compulsive commenter): 1 - For aeronautical use, AGMA quality number 10 or 11 is advisable. To reach that level of quality, I believe (please, those with more experience correct me if I am wrong) that some post-heat treatment grinding is unavoidable. 2 - Three gear systems (as in the Viking engines) have a complicating factor: the middle (idle) gear is subject to much higher cyclic loads in that the load the teeth get from the drive side is reversed on the propeller side, therefore if something is going to break due to fatigue, it is probably the middle gear.
Idlers are often much smaller gears,so I believe
that they are then stouter and stiffer, and also tend to run on a bigger(comparitavly) shaft again lending to a general overbuilt factor.
I can almost feel the looming correction.
 

Lendo

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Vigilante1. Having read all you provided and passing it on, it would appear I can't achieve a meeting of the minds on what we have discussed. My conclusion is there is much more to this that meets the eye. My first impulse is to split the difference, but being conservative I have taken the high road for calculations.
George
 
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