Prop mounting and torque?

Anyone know if I’m mounting these propellers wrong or what nm of torque the prop bolts are tightened to?
Looks like they slipped a bunch on first full power test. You can see the shaft extender dug in to the prop a little, am I missing something here?


I had the same issues. I don’t have a spec, but I giv’er has much as I can and haven’t had slippage. The Big slip I had was on the pair that have counter-torque which loosens the nut. Weve talked about doing something with multiple pins or other retaining features, which will require a custom prop or secondary process mods and an updated prop mount.

Thanks for the quick response @davek79 ! I wasn’t sure if I was missing a lock washer or something on that side of the prop. All four slipped similarly, I guess I just didn’t crank down the nyloc nuts hard enough. Thanks!

You’ll also find some of the “wear” is from the process of tightening them down - the props invariably turn if you’re holding them while torquing

I had the same issue; the prop slips and gets eaten by the fixation, or the fixation prints into the wood.
So I use a better way than friction to transmit the torque from the shaft to the prop:

  • I drill 2 holes of 3mm diameter and 12mm deep around the center of the prop on a 22mm diameter.
  • I press 2 tensioning pins of 3x16mm into those holes.
  • The pins match with the much larger holes in the body of the drive shaft, so the drilling doesn’t come too accurate. After some degrees of slip the pins went through the play and will take over the transmission of the torque.
    The tension pins are very light and at a small rotation diameter, so have no significant impact on the balance of the prop. At least I don’t experience any trembling.
    I made a small steel drilling mold with a 10mm center hole and 2 holes of 3mm around it. I put the rear of a 10mm drill through the propellor and place the mold over the drill end. Then drill the 3 mm holes through the mould, so they are at the correct diameter and exactly opposite each other for balance. Then I press the pins into the prop with a vise. This works very quickly. See below pictures.

    Pins to transmit the torque:

Detail of a tension pin:

Mold centered by rear of 10mm drill stick through heart of propeller.

Drilled holes:

Push pins into prop with a vise, so they stay straight and you can easily control that they stick out 4mm:


I tighten them tight enough to get a good imprint into the wood and that imprint and friction keeps them from slipping. Been using this technique for over a year with no issues. We need to have a torque spec. I don’t have a torque wrench though so that wouldn’t do me any good. My threads are getting pretty warn from tightening the nuts so tight though.

Friction alone doesn’t work well so if you use a carbon prop which is too hard to get an imprint then pins would be a good solution.

Nice job with the jig and all.

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Looks very good

Had to repair a drone becouse the lack of reserveparts and came up with 2 wormscrews from the side:

It does force the propeller to not slip around also as not pull off from the axe, but not only weakens the propeller, also a bit the axe itself becouse of the short drilling into the axe itself.
Not sure which method will bring the better result as yours does not afect the stability of the axe and mine aditionaly would hold the prop when the axe should ever get snapped.
No idea if that big wood propeller will work as good as the plastic one of my drone with 2 wormscrews, used m4 ones for a minipropeller and would had to scale that for the big ones.

The stud is highly unlikely to break directly under the washer. It is much more likely to break at the base of the stud due to the leverage of the prop. But if you weaken the stud by drilling holes into it then it not only is more likely to break but if it does break it would break where you drilled it because you are creating a weak spot.

That 10mm stud is plenty strong if you don’t modify it. But if you make the modification and it breaks then you are putting yourself at risk of the prop striking a battery which could start a huge fire on your back.

The solution is simple… tighten the nuts! Or, make the modification Ralph did AND tighten the nuts. I’ve never had a problem with mine slipping and I’ve flown it almost every day for over a year.

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Good point
thats what i wanted to know
Had no choice with the drone but open ppg i have

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Since I will use 23x13 prop’s I have to put a 6mm spacer under the prop. I can’t use the
10mm nut so I put 6mm stainless steel helicoil inserts in the holes. Looks plenty strong,
even around the inserts there is only 1mm aluminum.

I still have to make a drill jig for my prop’s and washers to drill…


I’m wondering if the problem some are having with props slipping is due to power application technique. With electric there is a lot of torque so if you’re ‘popping’ the power off and on you get more slippage. Applying/letting off power smoothly would result in less instant torque and less/no slippage.
Also tighten the nuts!

No, the problem is that 2 motors are CCW and try to loosen the 10mm nut !
With CW rotation 10mm is plenty strong.
So these 2 nuts need more torque to secure…

Good solution would be that the CCW props have CCW nuts and standoffs.

Ok so the momentum of the CCW props would be trying to tighten the nut when power is applied and loosening it when power is cut. Opposite for the CW props. Therefore it seems plausible that the cause is not the motor torque but sudden drops in power. Or did you mean CCW as viewed looking back, at the front of the props?

CCW nuts and studs would be a nuisance (hell if you lose a nut!) but would work.

Same here. No problem.

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Perhaps this will help… I hold the motor with one hand while tightening the nut with a ratchet with my other hand. Once the nut is so tight that I can’t grip the motor anymore then I use the prop for leverage while still holding the motor. At this point there is enough friction to make this possible as long as you continue to hold the motor too. Basically I put my fingers on the ratchet and my thumb on the prop and squeeze.

Just get the nuts tight and they won’t slip. I’ve never had issues with slipping.

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Have you seen an issue with the threads on the shaft? Mine are all squished from tightening the nut and I’ve only ever held the motor until I can’t anymore. I’ve had to replace one of the prop standoffs due to bad threads. We ned maybe some torque specs for these nuts, or stronger standoff material. They are not holding up for me after only spinning the nut on/off a handful of times.

I try to limit how often I take the props on and off because of that issue. I would probably balance my props more often if my threads didn’t have so much wear. However, they haven’t warn to the point of needing to be replaced yet.

I have a batch 2 which has two piece prop standoffs. The stud that holds the two halves together is only 8mm while the prop stud is 10mm. Last week one of them broke through the 8mm stud so I am replacing all four standoffs with the new one piece design. Then I will have all new threads.

Note: The slipping happened when the standoff broke and the prop hit the frame.

Not sure how many people have a batch 1 or 2 but it would be a good idea to upgrade to the new standoffs. I hate to think what would have happened if the prop hit the batteries instead of the frame.

Did you order the prop stadoffs from Pdwhite through email? Because I don’t see them in the OpenPPG shop, nor in the GitHub liabrary. Can I ask what did they cost?

I just ordered them through email. I’m not sure the cost. I ordered other items too and he only told me the total.

Here it says 23 nm for aluminium screws

With aluminiumshaft the nut should also fit the material of the shaft.

02_bolt_tightening.pdf (322.1 KB)

So if we have an alushaft we need to use a alunut and the nm for that aluminium material.

As the wood propeller is soft and kompresses
It seems to be necessery to prevent slip.

Normaly you have 50% reserve with the norm nm.

As it is importand not to fail we should maybe try not to put to much force on the shafts and to use the right nut material not to destroy the shafts…

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