What do you do when friction isn't enought to hold the props?

Do you use screws on motors that support it? Just swap the props? Nylon screws, or plugs of some sort? If so, where can I get them?

2” props.. most motor shafts are gonna be 1mm.. I wouldn’t use screws.. (added weight and make the motors work harder)…
If ur 2” props do not have enough “friction” to stay on.. there are several “tricks” that help. ..
-dental floss between the shaft and prop hole
- heated sewing needle on hole sides to “melt”-deform
- super glue on sewing needle, spread on side walls to prop shaft hole.. ALLOW TO DRY.. then install ..
But the best..buy more props..

I always use screws on any prop/motor that has that functionality. I didn't at one point, then was flying in the rain one day and blipped the throttle during a powerloop, lost a prop and it cost me a vtx, camera and frame (60m drop on to hard ground). Always screwed them down after that. Once bitten, twice shy and all of that.

If you can screw them down, screw them down. As to what you use, up to you. I prefer flat head, pozi screws. Some use bolts. It seems every motor/prop size seems to use different size screws. If you don't have them on some motors and you crash, you can lose the upper shaft in a crash, I think that was pointed out by mstc to me in reference to HM 1404 motors. LemonyLeprosy told me long ago to always use them if you can. So I do and I haven't broken any shafts, but unfortunately it doesn't stop you breaking frames.

As to extra weight, do the calcs on your build. Work out the potential thrust of your motors at 50% and 100%, so most motors that you would use on a build supporting 2" props that also have holes are going to be reasonably powerful, probably 1103 and upwards, so thrust wise 300-800g, build weight 70-80g, weight of very small prop screws I use on one of my Flea builds (2" props on 1202.5) 0.08g x 8 = 0.64g.

So for me my quad weighs 70g dry, 106g AUW, produces roughly 500g thrust at 100%, adding 8 prop screws makes the dry weight 70.64g. Total amount this affects the flight characteristics of the quad, sweet F.A. Maybe adding prop screws to a 65mm whoop or 75mm whoop might have some affect.

Do the calcs for your own build, ie, take a scientific approach to it. That is where you should start from when deciding whether to add more weight. For me on any build I have ever made that allowed prop screws to be used, it has had a negligible effect on flight characteristics, because I am adding not much more than half a gram of weight. Also the likelihood of being able to use said screws on 65mm and 75mm whoops is pretty low since they don't tend to use motors that are big enough to take a screw or bolt.

Titanium screws M2*7

1404 motors oh hell yeah.. my twig xl is a 3” 4s ripper.. and yes at first I flew it without screws.. but like u said.. one good “blip” and your earthbound.
Granted my babytooth is also 3”.. it is flying strictly 1s lipos.. and no screws .. I think it honestly depends on motors and power..

To be fair my Meteor85 came without prop screws on 1103 and I flew it that way without really knowing any different until Lemony schooled me on it and I checked the props and one basically fell off when I touched it. The one that ejected the prop was the 1202.5 on 3S. I've also ejected one on the same motors on 2S, but those are reasonably powerful motors.

I wouldn't disregard advice of not using them. Use common sense. Since you can potentially get builds that use 2" props and 3-4S power, you would need them on that level. But the way i would work out whether i need them is a get an estimate of thrust for the motors you use and total weight of the quad. If it's a small amount per motor and you have a fairly low thrust ratio, then I wouldn't bother since it's unlikely you would create enough torque to pop them off, even if you have reduced the friction coefficient by flying in the rain or some other condition that adds potential lubrication. On higher cell counts and more powerful motors, always use them. So at a 4:1 thrust ratio on say 1106 (and greater) motors you will have to use them.

The other thing is shafts. If the upper shaft on the motor isn't very strong, then using screws will go some way to avoiding snapping it in a crash. The 1404 example i made. Not all shafts are built well. i admit to not buying small motors with 1mm shafts full stop. i always buy 1.5mm shafts after watching a video by JB back when i first started, about that subject.

I don't know if that is too quick and dirty an approach to the subject.

The newer HM 1404 shafts fit so snugly, you don't need prop screws to keep the props on the shaft, however you get a different problem if you don't use prop screws - the shafts snap off and get carried off by the prop...

For micros, 3S and up its just too easy to lose a prop in a throttle blip or a light prop-strike without prop screws (unless its a pusher, then you can be braver). For 2S, on light builds I think you can mostly get away with it (I never run any prop screws on my light 2S micros), but where you lose out is if you are trying to turtle out of a tree you'd probably have a better chance with prop screws.

I think @ph2t suggested using a sharp tool to scuff up the inside of the prop hole, this will give it a little more grip on the shaft without any bad effects on balance. Have not tried that myself.

.. I just realized.. my Tinyhawk freestyle.. I have always used screws.. and it was a 2s 2.5” setup.. it was light, and the rush props had some pitch.. but it had screws..
Now, I was given a quad, it was kinda like a cini-quad, the frame looked like chrome.. it was a 4s -2” rig.. heavy (POS).. but it had screws..
I guess application and how u fly will help dictate whether you use or not use them..
Kinda like props… I used to purchase the “dark grey, black” props for my rigs.. thought they looked bad ass (hanging on my wall)… until you can’t see your rig 5 feet in front of you in tall grass…
I get the loudest, brightest, most contrasting I can find now..

2" is the biggest I'll go with no screws. It's a really light build that I only fly over grass, so crashing really hasn't cost me anything. Have ejected 3 props this year.

If the motor is a T-Mount, that is it has M2 machine thread holes 
in the bell housing, then I use M2 bolts of an appropriate length. 
About 90 percent of my props have a 5mm thick hub and take a
7mm long bolt, however, I have some props with hubs that are 
NOT 5mm, so I use a bolt that is +2 mm longer than the thickness 
of the prop hub.

The only instances where I don't use prop bolts is when there 
are no holes for them as in the case of tiny motors where I don't 
have an option.

I use standard, black steel, bolts most of the time since they work 
fine. Nylon bolts are lighter, but will shear if the prop catches on 
something and then you have to get the broken bolt out of the bell
housing. That said, I have ordered some M2 * 7mm aluminum bolts 
to use as prop bolts. I thought about titanium, however, the bolts 
are not that much lighter than aluminum, yet, quite a bit more 
expensive. So, I just can't see the value in them for this use case. 

titanium is stronger than aluminum.

(18-Feb-2024, 04:47 PM)LiPoFly Wrote: titanium is stronger than aluminum.

Where do you order them from, grade 2 or grade 5?

Info here, they take quotes for orders but no prices listed so expecting high?:
https://www.extreme-bolt.com/titanium-fa...anges.html

...wish were possible to inexpensively order a 100 pack of m2x7 for prop nuts, and others likewise for motor mounting...

(18-Feb-2024, 04:47 PM)LiPoFly Wrote: titanium is stronger than aluminum.

Hi LiPoFly,

Yes, titanium is stronger than aluminum, but not enough so to warrant paying
through the nose for them especially for pop bolts. So far, I have never had 
a prop bolt come loose or come out during flight. Even the weight is not a
huge concern as I use the black steel bolts and sometimes stainless steel
depending on the day, the build, and what I happen to have on the bench.

If one is really trying to shave off grams, I would say that lighter bolts
could be used for motor mounting and frame assembly. So, how much
weight would I save using titanium or even aluminum instead of the 
steel bolts that I use? A couple of grams?

Every time that I look into titanium or even aluminum bolts, there are 
two things that displease me and turn me away. The first is the cost.
Titanium is outrageous. Even aluminum bolts cost way more than the 
steel ones that I buy in assortment boxes. 

But the real kicker is that I have not found titanium nor aluminum bolts
in assortment boxes where you get a whole range of sizes in one divided
container. Sweet !!  With buying individual sizes, you can't buy just a few,
you have to buy 50 or 100 of them. WOW. Now, what if you want a range
of 10 different stepped sizes. BOOM. The cost just rockets through the
roof. If I could find decent assortment box, maybe, the cost would be
a bit more...well...palatable. 

If you find a good assortment pack of either titanium or aluminum for
a reasonable price, then please let me know. 

Even though I am weight conscious, I am not overboard with it. As long
as I can keep the dry weight less than 150 grams, then I am fine with it.

Later, iFly   

(18-Feb-2024, 04:47 PM)LiPoFly Wrote: titanium is stronger than aluminum.

If you are talking about the pure element, maybe so. But in manufacturing typically an aluminum alloy would be used, and for that it seems something like T7075 may not be any weaker/heavier than a Titanium alloy?

Quote:Compared to grade 2 titanium,  7075-T6 aluminum is 33% lighter and has a higher tensile strength, strength-to-weight, and stiffness-to-weight. Aluminum can also be anodized - effectively growing an ultra hard, ultra durable skin on the outside of the metal.

https://morselspork.com/blogs/journal/yo...o-titanium

Or maybe not?

Quote:Although titanium is about two-thirds heavier than aluminum, its inherent strength means that you need less of it. In fact, you need a fraction of the amount of titanium to get the same physical strength you would get with aluminum...
In critical situations where every gram counts but you need strong parts, titanium is the way to go. Titanium medical components, complex satellite components, fixtures, and brackets all succeed precisely for this reason.

https://www.protolabs.com/resources/blog...-printing/

https://en.wikipedia.org/wiki/Ultimate_tensile_strength

Problem for me with aluminum screws is the head breaking off from crashes. Have not tried in m2x7 prop screws configuration tho...