glue on props

Hello Everyone,

Ok the only crashed I get now are when a prop falls off the quad will in flight.  It has cost me two cameras and a good amount of embarrassment.  It only happens once every 15 flights but I hate it.  So has anyone ever super glued the collet prop ad pater to there motor?  It seems even if the motor goes bad at some point a new motor comes with a new collet adapter.


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  • I know this is a little bit of a necro, but I wanted to post a follow-up, and I've seen a handful of posts on the topic in other threads as well.

    I ended up going with the E-flite adapters ordered through my local hobby store as planned, and I've been fairly satisfied with them.  Because so many people here suggest it, I did use a little bit of blue loctite on the threads.  And I've had no signs the adapters loosening.

    But the other day I got a little carried away tinkering with the PIDs and had a minor crash with a prop strike (vs. grass/dirt).  The prop was undamaged, but motor shaft was very slightly bent.  I didn't notice this at first, and continued to fly my quad after a quick check and PID adjustment (a later review of the logs clearly showed an increase in vibration).

    Well, a couple minutes later one of the other motors came loose.  I landed before it completely let go, and put the quad back on the bench for a full check and repair.

    Lesson #1: I should have put locktite on the motor mounting screws.

    Lesson #2: locktite does NOT work well with the E-flite adapters.  In attempting to get the prop off the damaged motor, I had to grip the adapter with pliers and destroyed it in the process.

    I disassembled the motor, straightened the shaft, reassembled with a new prop adapter, and went back to flying.  And started shopping for a better way to mount the prop.  I ordered some parts from rctimer to try out, and here is what I learned:

    The 45mm shaft they sell matches the original shaft on the 3DR 850kv motor.  Even with the E-flite adapter, this leaves about 4mm of excess between the adapter and the top of the motor.  This excess just makes it that much easier to bend the shaft.

    They also sell a 41mm shaft.  I ordered a few, and they appear that they will work well with the E-flight adapter.

    They also sell a 37mm shaft, which appears to be the best length to use with the 3DR adapters (although I recommend against it for the reasons in my previous post).

    And lastly, they sell a 31mm shaft, which is flush with the top of the rotor.  This works with their new bolt-on adapters., which fit the 3DR 850kv motors.  I ordered one of these to try, and put it on the motor for some bench testing tonight.  I have two minor complaints, but my overall impression is favorable.  I intend to flight test the adapter and probably order a full set.

    My complaints are first that the spacer (needed for thin props like an APC 10x4.7 SF) has a large center hole, meaning it is about impossible to perfectly center, and second, with said props the prop shaft is just long enough to extend into the through-hole for tightening the spinner nut.  That can be fixed with a dremel.  Also note that the adapter does not seem to be available in a reverse-threaded version, which is too bad.

    Lastly, I was curious about the weight; the bolt-on adapter is also about 3g heavier than the E-flite adapter, but the shorter shaft is about 2g lighter.

    Hopefully this info will be useful if anyone else is looking for alternate prop adapters.  Note that if you want to change the shafts on your motors, you'll need some sort of press.  There are details/videos about how to do that if you search.
  • I received my 3DR quad kit and started building it this weekend, and I've got a problem with the prop adapters right off the bat.   It's not just that they're on the cheap end... the ones I received with my motors (standard 850 kv, now colored blue) aren't even flyable.

    I don't know if "bent" is quite the right term, but the situation is that the axis of the prop shaft portion of the collet is not aligned with the motor shaft hole in the collet.  This causes the whole thing to wobble when the motor turns.  Two of the four in my kit are so misaligned that it is visibly obvious when turning the motor by hand.  The other two are misaligned enough that you can see/feel it when spinning the motor electrically.  These are not suitable for flight.

    I also happen to have a prop adapter from an old E-flite motor that also happens to have a 3.17mm (1/8") shaft.  The E-flite adapter has no detectable wobble at all.

    There are also some other key differences:  The E-flite collet fits loosely on the shaft until the spinner nut is tightened.  The 3DR collets have to be pushed on with force, and are then difficult to remove.  The depth of the motor shaft hole on the 3DR collets is about 7mm, but I'm only able to push the collet ~5mm onto the shaft using reasonable force.  I know that some manufacturers have actual 3mm adapters, and I suspect that the 3DR motors might have shipped with 3mm adapters for a 3.17mm shaft, although I cannot measure the inside diameter of the hole precisely enough to tell if it's that, or just a tolerance issue.

    Next, as mentioned the 3DR collets' prop shaft holes are about 7mm deep.  The E-flite adapter has a hole that is about 10mm deep, and unlike the 3DR collet, can put pushed all the way onto the shaft.  10mm of depth (E-flight) compared to 5mm of usable depth (3DR) gives double the surface area for gripping the motor shaft and leaves less of the motor shaft exposed.

    So, I agree with the sentiment that the E-flite prop adapters are higher quality.  I also agree that bolt-on adapters would be preferable, although I suspect they might increase the amount damage resulting from a prop-strike.

    I'm a bit disappointed with my current situation, but I'm going to see if I can get some more E-flite adapters (or some other suitable alternative) at one of the local hobby shops.

  • The 'prop saver' idea is a good start.

    My suggestion of through the wrench bar hole would not work if the retaining nut were actually only a nut and washer. For that arrangement, the 'over the hub' method is the only solution.

    With a spinner nut, a 'thru-hole' solution would also retain the nut in the event of a rotational force failure- a situation that counter-turn threads would resolve.

    Now is a good time to reveal a previously edited photo of the thru-hole idea...


    Clipping off the motor shaft would be a good start and reduce the amount of retaining wire/strap/material.

    I am willing to bet that somewhere, someone has a bolt on adapter (previously shown) that fits this magnet housing. We would then just cut off the shaft, bolt it on and remove one failure point from our machine.

    All we need then to worry about is the loose nut behind the wheel sticks.  ;)


  • Maybe the simplest approach is to use ESC feedback like this:

    The first thing that would happen if a collet started to slip is the prop would free spin and the motor should speed up instantly or cause some recognizable change. If it's a hex or octo then the esc could shut down before sending the prop flying off and maybe into other props.

  • T3
    Nice drawing Doug. Thanks for sharing.
  • Ok folks, for what it is worth I have posted my cross-sectional sketch of a collet-type adapter.


    Pros will probably <yawn>...

    It is for the newbies and others that may not quite understand what the device is supposed to do. I hope we can use it to  illustrate proper installations of these gadgets and perhaps standardize the phrases used to discuss them.


  • The collet-type adapter is not exactly flawed but probably not the best choice for a multirotor. All too often we put nickle-and-dime parts on our very expensive aircraft and want to blame the people who make the parts. Again, cheap ain't better, or best in this case.

    Is there a better device? Absolutely.

    As previously mentioned, multirotors are totally unforgiving at tossing a prop, by any means. The numbers alone will increase the risk of a prop adapter failure. Add to that the variance in quality between the motor shafts and adapters and the results are what we are experiencing.

    The simple way to make sure our props are secure is to use another adapter. There are several makes now available that attach directly to the motor housing (rotational housing) IF you can find one for your motor.

    Such as...


    Of course this type adapter, to be totally immune to rotational forces on the nut, would have to be in two types: CW and CCW threads.

    Invariably someone will mix the two up, with predictable results OR they will mix up their ESC/motor wiring and mix up motor direction with directional adapter types.

    I would hate to see any 'regulation' on this subject. It could be that clubs set (or have already) local rules for prop adapters to cover insurance risks. It could be that large organizations (AMA, IRCHA, etc) petition the manufacturers for a better solution. I certainly wouldn't want the Federal Government to get involved. None of us wants anyone to be injured, much less hang an expensive DSLR camera under an aircraft that could toss a prop at any time.

    +1 with Scott on the probable cause. The aluminum will change size faster than the steel of the motor shaft. If the fit was 'good enough' before, it certainly will be less that that after getting cold.

    Could the collet-type be made cheap enough if out of a steel alloy? Would the slight increase in weight be a 'no sale' for the weight-concious hobbyist?

    Stay tuned dear viewers. These and more questions will be asked in the next episode of "As the Propellor Turns"!


  • I have never cared for the aluminum clamp type of prop nut.  When you tighten them really well,  you may be stripping the aluminum threads.  Then add to the problem by using the prop on a motor turning in a direction which will cause the nut to turn in the loosen direction.  THINK OF THIS: a table saw uses a reverse thread nut.  And the nut is NOT aluminum !  Every turn of the saw blade will tighten the nut.   They don't want that saw blade to come off.  Multi copters should ONLY use prop screw shafts and real nuts!  (IMHO)

  • I have never had a prop come off until today when it happened twice on two different props. On one, the nut came off leaving the collet on the shaft. Recovered the prop but not the nut. The other the entire assembly came off teh shaft and was recovered. I suspect the cold caused differential expansion and contraction of the shaft/collet/collar (or whatever it is called) around the collet and the nut. Luckily no real damage.

  • THIS fellow used a program on a cell phone to measure the vibrations of his efforts to balance props and propellor adapters.

    He went throught various quality adapters, clipped off the motor shafts, and spent more time testing than flying it seems.


    He was just spinning up the motor and adapter in these tests. One problem is knowing if the rpm was the same between tests. I have noticed resonance effects at different rpms. Again, 'the sound' is where it tells on the system.

    No expectations Tim. There are so many places to spend time in this hobby when we should just be flying and, of course, trying not to crash.


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