11 or 12 tooth pinion for 8mm shaft?

[trillian]

I am looking for an 11 or 12 tooth mod 1.0 straight cut pinion for an 8mm motor shaft. So far I have seen slant 11 and 12 tooth for the E820 and most of my Google searches have been a waste of time.

[10x]

Hello trillian
What motor have you got, If you can get a 6mm pinion it might be that you you can change shafts or get your shaft turned down to 6mm....Sorry probably not the answer you were after...

[trillian]

It's a Pyro 800 and I'd like to keep the 8mm shaft because it's going on a heli with a motor mount that does not have a pinion support. Plus, it's a bit of a hassle to change shafts on the Pyros.

Worst-case I can probably get a 6mm pinion drilled out but would have thought there would be more choices now for 8mm motors.

Hello trillian
What motor have you got, If you can get a 6mm pinion it might be that you you can change shafts or get your shaft turned down to 6mm....Sorry probably not the answer you were after...

[Grumpy]

Isnt a pinion that small on a motor with that much torque asking for trouble?.. Plus there surely won't be much metal left if you bore it for an 8mm shaft?

[trillian]

Isnt a pinion that small on a motor with that much torque asking for trouble?.. Plus there surely won't be much metal left if you bore it for an 8mm shaft?

Well you only lose 1mm of pinion metal thickness. In this case the main gear is very tall so there's a lot of material engagement between the pinion and gear. Also it will be fairly low headspeed so not crazy loads.

I have just seen somewhere a Kasama pinion bored out for 8mm and I am going to contact the person that did it, so that may be the solution as I have a few Kasama 6mm pinions already.

[Grumpy]

So i just worked it out:

The pitch circle diameter of the pinion = Mod x Number of teeth = 1.0 x 11 = 11mm PCD

The depth of the teeth of is 1.25 x mod = 1.25mm

So the diameter of the 'dedendum circle' (i.e to the root of the teeth) = PCD - 2x1.25 MOd = 11mm - 2x1.25mm = 8.5mm dedendum circle



So it's impossible to have a 11t mod 1.0 pinion bored for an 8mm shaft. There would only be 0.25mm of metal between shaft and the root of the tooth (not allowing for clearances), the teeth would rip off. A 12t wouldn't be much better, that would only have 0.75mm of metal below the tooth, if that would be safe or not i'd not like to say.

Although the difference between a 6mm shaft and 8mm may not sound like much it would be a 500%+ increase in strength (1.25mm of metal vs. 0.25mm) in the case of the 11t pinion.

[10x]

It's a Pyro 800 and I'd like to keep the 8mm shaft because it's going on a heli with a motor mount that does not have a pinion support. Plus, it's a bit of a hassle to change shafts on the Pyros.

Worst-case I can probably get a 6mm pinion drilled out but would have thought there would be more choices now for 8mm motors.

The trouble is that nearly all are now using slant/herring bone gears...

[trillian]

So it's impossible to have a 11t mod 1.0 pinion bored for an 8mm shaft. There would only be 0.25mm of metal between shaft and the root of the tooth (not allowing for clearances), the teeth would rip off. A 12t wouldn't be much better, that would only have 0.75mm of metal below the tooth, if that would be safe or not i'd not like to say.

Well it's not impossible because there is an 11 tooth 8mm pinion for the e820, although it is a slant tooth. There is a little leeway in the depth and shape of teeth. But even so it may need to be 12 tooth.

[Grumpy]

Interesting.. i can only guess that they use a non standard tooth depth. Even so it must be right on the edge of what's do-able.

[10x]

Just measuring a E820 pinion at 11t the wall thickness on a 8mm shaft is 1.1mm, but using Grumpys numbers i think that they are 1.25
mod teeth...

[Grumpy]

So i dug down in a bit more detail. My calcs neglected a factor called 'Coefficient of profile shift'. This has the effect of reducing the depth of the teeth that I used in the calc. The coefficient varies according to tooth shape but it would seem that typically it would mean that the tooth 'dedendum' would end up at about 0.65mm rather than 1.25mm that I assumed. That in turn would give an extra 0.6mm of metal between base of tooth and shaft, so around 0.85mm for the 11 tooth.

That at least comes close to whats been measured! Still pretty tight though.