Infraction Does gear size impact performance?

[jondilly1974]

Wondering if the size of gears we choose affects speed run performance. For instance, we all know the gear ratio is a huge factor, but what about running 34/34 vs 39/39? Does the added weight of a 39T vs a 34T gear make any difference, assuming your motor mount allows for both. What about 40/40 vs 29/29, or an even larger delta? Does gear weight matter? Does tooth engagement matter? Or do you think it’s such a small factor that we aren’t likely to see an impact?

I plan on testing this very subject soon.

 

[MAVERICK@2]

Wondering if the size of gears we choose affects speed run performance. For instance, we all know the gear ratio is a huge factor, but what about running 34/34 vs 39/39? Does the added weight of a 39T vs a 34T gear make any difference, assuming your motor mount allows for both. What about 40/40 vs 29/29, or an even larger delta? Does gear weight matter? Does tooth engagement matter? Or do you think it’s such a small factor that we aren’t likely to see an impact?

I plan on testing this very subject soon.

That’s some deep stuff man

I am very interested in what you find out

 

[CameronCodes]

i belive that more teeth =top speed where as less teeth = quicker acceleration

 

[K-BASH]

I guesstimate about a 12-15 gram difference between 2× 34t & 2×39t.half ounce in a 11lb car .should show on logs if passes where identical. Physics tell me more energy is needed to move heavier, larger items.jd you now just as much as me about THE SMALL THINGS when it comes to gaining 1 mph.very Interested in testing this one.

 

[Monster Dork]

I don't think there's much to find here. The tooth profile is established and all gears in 6s have a module of 1. Strength gains are of little consequence here, the system is strong enough already. Pressure angles will change with different sizes, but the strength overhead already built in makes it a minor factor. There is a little difference in mesh forces, but that's in the weeds, just below rotating mass. Involute gears are an interesting subject, lots to learn, but the engineering has already been worked out for us on our RC cars.

https://khkgears.net/new/gear_knowl...ut-parameters-that-determine-gear-shapes.html

https://www.cedengineering.com/userfiles/Basic Fundamentals of Gear Drives R1.pdf

https://www.cs.cmu.edu/~rapidproto/mechanisms/chpt7.html

 

[3d-rc.myshopify.com]

I have wondered this same thing myself. I know in 1to1 cars it does make a difference a smaller gear set of the same ratio is less moving mass but in rc cars not sure it makes much difference. 1 way to find out lol back to the lab dilly goes lol

 

[Notoriousone]

Thought about this as well, I'm not sure if the performance would be different but I think other things like the how weight of the gears affects the handling, and the motor heat generated would be different. In 1/1 cars and motorcycles the size and weight of the flywheel has a huge effect on how fast the engine revs, it should be the same for larger heavier RC gears to some extent

 

[SrC]

Wondering if the size of gears we choose affects speed run performance. For instance, we all know the gear ratio is a huge factor, but what about running 34/34 vs 39/39? Does the added weight of a 39T vs a 34T gear make any difference, assuming your motor mount allows for both. What about 40/40 vs 29/29, or an even larger delta? Does gear weight matter? Does tooth engagement matter? Or do you think it’s such a small factor that we aren’t likely to see an impact?

I plan on testing this very subject soon.

Excellent point made.
I've seen this discussed elswhere on the web before. I agree 1:1 is just that, 1:1 (Spur/pinion).
In theory, it shouldn't matter. But I feel the larger the match gears, creates a Fly wheel effect to the drivetrain. Is that a pro or a con? IDK.
Also, at some point, does meshing 20T with 20T become less efficient than a 40T/40T. It may just be a wash? I always felt larger gears wear less, last longer. Run cooler from less friction. Larger gears rotate less for the same motor Revolution. Smaller gears rotate more for a motors full revolution. If I got that right. Hmm??
Great topic.

 

[K-BASH]

Can't wait to see what you come up with to test this much anticipated experiment.JD you are the certified arrma scientists.ive put alot of thought into this an keep getting stumped by the pros & cons..in the end i think weight will become the judge. I believe that anything performance oriented weight is everything. Just my 2 cents

 

[jondilly1974]

Can't wait to see what you come up with to test this much anticipated experiment.JD you are the certified arrma scientists.ive put alot of thought into this an keep getting stumped by the pros & cons..in the end i think weight will become the judge. I believe that anything performance oriented weight is everything. Just my 2 cents

I agree weight matters, but how high of weight does it need to be to be a factor.

 

[3d-rc.myshopify.com]

I agree weight matters, but how high of weight does it need to be to be a factor.

I know when I used to race I would have the same plastic spur and about 8 1/8 holes made a huge difference on the decal of the motor. It would almost feel like it would apply brakes when I would let off. Was great for serpentine turns. But the solid spur was great for long sweeping tracks it would carry speed through the turns much better off throttle.
I would assume for speed runs the heavier larger sets would help not shake the tires loose for a beginner. I also know brushless motors lose power in the upper band so maybe a big enough change might get an extra mph or 2 for less rotating mass just an assumption.

 

[ABabyEater]

While you are at it, if you have identical form factor motors from the same manufacturer, it would be interesting to see if when geared to achieve an identical final drive a higher KV geared down or a lower KV geared up is more effecient.

 

[rotauq]

While you are at it, if you have identical form factor motors from the same manufacturer, it would be interesting to see if when geared to achieve an identical final drive a higher KV geared down or a lower KV geared up is more effecient.

Lower kv had a very marigal almost neglectable advantage vs high kv.


As for gear sizes, a JD experiment will certainly tell us. I see may pro's and cons. Like @3d-rc.myshopify.com mentioned from his racing days the added weight has it's effect on inertia too.
I also know from my 2stroke tuning in the past that the lighter flywheel only effects acceleration, not top speed.

 

[MAVERICK@2]

Like I stated before this is a very interesting topic

But I think we are just splitting hairs and the outcome will not be that drastically different

But this is not the 1 to 1 size world we are taking about in comparison your r/c has very little weigh. A very small amount amount of wind can change the reading or outcome in a race

I think this is more relevant for things like drag on the motor or battery run times. Long endurance racing I think is where this would be most helpful

This reminds me of a story about keeping AA batteries in the refrigerator to keep them from discharging. And yes it helps but do you really plan on keeping a battery for 20 years to reap the benefits

Just my thoughts

 

[LibertyMKiii]

I agree that the weight of the gear itself likely would only impact acceleration and not the final top speed.
Any differences wouldn't be measurable from run to run as the difference is so small.

 

[SrC]

^^^ I think a CC data log could very well distinguish a difference between large 1:1 and small 1:1 gears. However slight it may be. And to what benefit, IDK. Amp draw alone, should in theory be less with a small 1:1 gear combo. May depend how, what and where you drive.

 

[Edough13]

So the one thing that's been really interesting to me is that we have been running almost identical setups. Both running Castle xlx2 and 1717 1650kv setups in basically the same platform, Limitless and Infraction. Yes body is different, both running foams, both using a throttle speed limiter for good pulls etc. But you running 36/39 is pulling what like 444+A at 143mph where I'm running 34/34 and only getting 355A at 144mph Been wondering for a while why my Amp draw is soo much lower than yours when the setups are very very similar? Wondering if this has to do with running smaller gears, or is it the Pinocchio spool setup I run smoothing out the center driveline that much? Also we run different packs but would that warrant 100A difference? Just been thinking about this and wondering why they are so different.
Here's your log

And my log

 

[jondilly1974]

So the one thing that's been really interesting to me is that we have been running almost identical setups. Both running Castle xlx2 and 1717 1650kv setups in basically the same platform, Limitless and Infraction. Yes body is different, both running foams, both using a throttle speed limiter for good pulls etc. But you running 36/39 is pulling what like 444+A at 143mph where I'm running 34/34 and only getting 355A at 144mph Been wondering for a while why my Amp draw is soo much lower than yours when the setups are very very similar? Wondering if this has to do with running smaller gears, or is it the Pinocchio spool setup I run smoothing out the center driveline that much? Also we run different packs but would that warrant 100A difference? Just been thinking about this and wondering why they are so different.
Here's your logView attachment 172860And my logView attachment 172861

Are you running GP5 diffs? The truck body and my big rear wing are surely a lot more drag too. Not sure if that is 100A worth of drag but it could be. Also, what elevation are you at? Your air could be a lot thinner.

 

[SrC]

@Edough13, amazingly, I can see that, the very similar logs you describe. You are running more efficiently. Temps are lower . But that may be due to environmental Temps, Aero, and subtle drivetrain differences. Lipos may be a factor also.

 

[Edough13]

Are you running GP5 diffs? The truck body and my big rear wing are surely a lot more drag too. Not sure if that is 100A worth of drag but it could be. Also, what elevation are you at? Your air could be a lot thinner.

Yep come on you should know I've got gp5's Also running BSR 103mm foams. I would almost think they would even out in the drag aspect as I'm also open wheel where your not so we both have some degree of higher drag. I'm at about 4200ft elevation and been running in low 60's for temp. Just seems for some reason your system is being stressed a lot more than mine. Not sure if Perfect Pass is that much different than your throttle speed feature and that's possibly it just really don't understand why the two setups are not running a lot closer numbers in the logs?