Motor shaft size dilemma

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Horhe

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Arrma RC's
  1. Felony
  2. Limitless
Hello everyone :)
As some know, I am working on some speeduning builds and in the process I realize how much I don't know.
One of the recent issues that came to my attention as I was searching for TP motors in Europe is selecting the size of the motor shaft in my case between 5mm and 8mm.
Now, so far I've ordered pre-build motors and I've accumulated these:
- TP 4040 CM 1850 kv - 5mm
- TP 4070-CM 2200kv (8S) - 5mm
- Castle 1721 2400kv - 8mm

Up to this point I've only done three speedruns, with the following results:
1. 116mph (with TP 4040)
2. 133mph (with TP 4070)
3. 140mph (with Castle 1721)

Now in each I used different gearings and setups and this was all done (besides the fun) to learn more about the differences and impacts of various parts, so I am not putting the speed increases on utilizing different motors.

But now, my questions / dilemmas are:
a. What is the impact of having a 8mm motor shaft vs a 5mm motor shaft on speed?
b. How big/relevant is this impact if any?
c. From what point (speed) does it actually begin to be relvant?

I ask because I find it more convenient to get 5mm shaft motors, also because 8mm gears are SELDOMLY available in Europe.
Please share your opinions:)

And thanks :)
 
Personally, I much prefer the beefiness of 8mm shafts. The M5 grub screws in 8mm gears are so much more robust than their M4 counterparts in the 5mm gears. There's just no comparison. I linked you up with 8mm gears so that should no longer be an obstacle :)

As to your questions:
a) To my mind, none. I don't think it impacts speed even a little bit. Most 5mm shafts are actually ground down 8mm shafts.
b) See answer "a" :)
c) See answer "a" :LOL:

I think at some level of power (I can't give you any specific number) it becomes beneficial to run 8mm shafts so you don't snap one off. I could see that happening under adverse conditions with 15-20hp motors (I suppose 10hp could also be sufficient to get the job done, I was just reaching a little higher). I've never had that happen myself but I have heard of others snapping 5mm shafts.

Disclaimer: These are just my opinions based on my own experiences with 5mm & 8mm motors.
 
Personally, I much prefer the beefiness of 8mm shafts. The M5 grub screws in 8mm gears are so much more robust than their M4 counterparts in the 5mm gears. There's just no comparison. I linked you up with 8mm gears so that should no longer be an obstacle :)

As to your questions:
a) To my mind, none. I don't think it impacts speed even a little bit. Most 5mm shafts are actually ground down 8mm shafts.
b) See answer "a" :)
c) See answer "a" :LOL:

I think at some level of power (I can't give you any specific number) it becomes beneficial to run 8mm shafts so you don't snap one off. I could see that happening under adverse conditions with 15-20hp motors (I suppose 10hp could also be sufficient to get the job done, I was just reaching a little higher). I've never had that happen myself but I have heard of others snapping 5mm shafts.

Disclaimer: These are just my opinions based on my own experiences with 5mm & 8mm motors.
Thanks for answering :) And for the hookup :) One of the issues is higher T 8mm gears, in case I decide to do a test with lower kv motors...but hey...ultimately I will just get them from the States.

That's one interesting aspect...snapping. I would be VERY curious to find out under what conditions (speed, terrain, etc) the snapps happened.
Has anyone here snapped a 5mm (or 8mm for that matter) motorshaft? If so, under what conditions?
Thanks a bunch.
 
Thanks for answering :) And for the hookup :) One of the issues is higher T 8mm gears, in case I decide to do a test with lower kv motors...but hey...ultimately I will just get them from the States.

That's one interesting aspect...snapping. I would be VERY curious to find out under what conditions (speed, terrain, etc) the snapps happened.
Has anyone here snapped a 5mm (or 8mm for that matter) motorshaft? If so, under what conditions?
Thanks a bunch.
They have up to 49T gears. If you need larger still then yeah, SAGA and Powerhobby will be your best bet. I think they go up to 54 or 56T.
 
They have up to 49T gears. If you need larger still then yeah, SAGA and Powerhobby will be your best bet. I think they go up to 54 or 56T.
Speedtek makes a 60t now. 😂 for extreme measures 😝

Screenshot_20220930-075945_eBay.jpg
 
Thanks for answering :) And for the hookup :) One of the issues is higher T 8mm gears, in case I decide to do a test with lower kv motors...but hey...ultimately I will just get them from the States.

That's one interesting aspect...snapping. I would be VERY curious to find out under what conditions (speed, terrain, etc) the snapps happened.
Has anyone here snapped a 5mm (or 8mm for that matter) motorshaft? If so, under what conditions?
Thanks a bunch.
I snapped a 5mm shaft on a brand new tp 4060cm. Just doing slow circles & figure 8s trying see if a new setup was OK- turns out it wasn't

20220814_130044.jpg


20220814_141256.jpg
 
Surpasshobbyusa.net has large pinions too but I don't know if they ship outside of the US. You can also find their pinions on eBay from Chinese sellers. Surpass is cheaper than saga too.
 
Dang! Thought TPs were all dat and a slice of bearing bread? :ROFLMAO: :ROFLMAO: 🍻

Hope you have a good Friday bud! (y)🍻✌️🌲🌲😁
I hope they are cuz I just put a new 4060cm w/ a 8mm shaft in the Toe Cutter. The 8mm shaft sticks out a little more than the 5mm did tho- had to move the xlx2 just a little bit to accommodate. Just barely clears, 120 here I come!!😀🤞
Hope you have a nice little Friday as well!!😁🍻🌲🌲🤘

20220928_183729.jpg
 
Yea snapping a shaft has to be rare AF. I've never had it happen, and I lost count of how many TP motors I have. At some point I started to get 8mm shafts though and for the same reasons @Diem Turner listed. It's also easier to find larger sized pinions in 8mm.
 
Surpasshobbyusa.net has large pinions too but I don't know if they ship outside of the US. You can also find their pinions on eBay from Chinese sellers. Surpass is cheaper than saga too.
Thanks for the tip! Will check them out!
Yea snapping a shaft has to be rare AF. I've never had it happen, and I lost count of how many TP motors I have. At some point I started to get 8mm shafts though and for the same reasons @Diem Turner listed. It's also easier to find larger sized pinions in 8mm.
I agree it has to be a rare occurence. It's probably easier to find larger sized pinions in 8mm in the States though. In Romania it's basically impossible to find large / larger sized pinions for anything (5 or 8). Lucky I was pointed in the right direction by Diem Turner that actually has large sized pinions in the EU so at least theoretically they come faster and I don't have to go through the cumbersome customs process that I go through when I order from the States.
But for my lower kv motor experiment, I may need very large pinions and I guess my option is still only the USA.
Thanks.
 
Thanks for the tip! Will check them out!

I agree it has to be a rare occurence. It's probably easier to find larger sized pinions in 8mm in the States though. In Romania it's basically impossible to find large / larger sized pinions for anything (5 or 8). Lucky I was pointed in the right direction by Diem Turner that actually has large sized pinions in the EU so at least theoretically they come faster and I don't have to go through the cumbersome customs process that I go through when I order from the States.
But for my lower kv motor experiment, I may need very large pinions and I guess my option is still only the USA.
Thanks.
Just use smaller spur/spool gears. It'll be cheaper in the long run :)
 
And that's how you have started my NEW dilemma :)
What is the impact of different gearing combos resulting in the same ratio?
This never ends...the questions...:ROFLMAO:
Theoretically, it shouldn't make any difference in terms of speed. A gear ratio should be a gear ratio. The thing is, I don't think you actually have that many (or any?) overlap in the narrow band of gears available within the range of TTC of your motor mount. Something to consider is that going up one tooth on a pinion gear will not result in the same gear ratio as going down one tooth on the spur. There will be fractional differences between the two. This has the advantage of giving you many in between gear ratios instead of just continually going up a tooth on the pinion which can make the difference between a successful gearing up and over gearing once you start reaching the maximum available power of a given system.
 
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Theoretically, it shouldn't make any difference in terms of speed. A gear ratio should be a gear ratio. The thing is, I don't think you actually have that many (or any?) overlap in the narrow band of gears available within the range of TTC of your motor mount. Something to consider is that going up one tooth on a pinion gear will not result in the same gear ratio as going down one tooth on the spur. There will be fractional differences between the two. This has the advantage of giving you many in between gear ratios instead of just continually going up a tooth on the pinion which can make the difference between a successful gearing up and over gearing once you start reaching the maximum available power of a given system.
I think that in terms of speed, clearly there should not be that much of a difference. I was thinking about the impact on the electronics...that's one of the issues...and perhaps stress on parts...I don't even know :) :)
 
I think that in terms of speed, clearly there should not be that much of a difference. I was thinking about the impact on the electronics...that's one of the issues...and perhaps stress on parts...I don't even know :) :)
Just to be clear, I know nothing about mechanical engineering. There is probably more to it than what I'm saying. I'm just looking at it from my layman's vantage point with a broad understanding of things in general and that a 2:1 gear ratio should be the same no matter what size gears you're using. But no specific details. Perhaps someone with a deeper knowledge on the subject can give a better explanation of why one or the other is advantageous or if is, indeed, the same.
 
Just to be clear, I know nothing about mechanical engineering. There is probably more to it than what I'm saying. I'm just looking at it from my layman's vantage point with a broad understanding of things in general and that a 2:1 gear ratio should be the same no matter what size gears you're using. But no specific details. Perhaps someone with a deeper knowledge on the subject can give a better explanation of why one or the other is advantageous or if is, indeed, the same.
Well let me explain it. See, the max radius of the satellite gear divided by the number of teeth on the spur will tell you what the color blue smells like..........🤔🤯

Hell, I have no clue! :ROFLMAO: 😁🤪Gearing and shocks are on my homework/study list this winter. Those are my "areas of opportunities" as they say in the corporate world. 😂😜
 
Wow! I mean...that doesn't sound like it should happen. Could it be a factory fault?
Probably not. Think my mesh was too loose or the pinion grub screw came loose & everything got bound up. & with the power the xlx2 makes it was too much 🤷‍♂️ or maybe it was tp's fault!!😆
 
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