Replies to This Discussion

Permalink Reply by R. D. Starwalt on January 21, 2013 at 6:25am

Super catch David's Girlfriend!

It may not have been balance issue but rather a slipping collet. When spinning up to lift-off, the arm that dipped is the one that tossed the prop. If slipping, that arm could not match the command of the system.

This weekend, I was working with the power pod of a sailplane. The collet-type adapter was for a folding prop arrangement. It was a Fly Fly branded adapter. On a scale of 1 to 5, 1 being the worst, I would give the hardware a 3. The motor was a 5 mm shaft, the collet marked for a 5 mm shaft. The initial fit was terrible, absolutely bad bordering dangerous.

I mentioned to my friend (his sailplane) this discussion on prop tossing and my concerns about the prop adapter. He had a second unit, same issue. There were no instructions with the assembly and it appeared that to set the collet, the nose spinner screw should be tightend. No joy.

Dissappointed at the unit, I decided to disassemble it to discover the rest of the story. As it turns out, the collet should be set with a regular (aluminum) nut under the spinner! The screw in the nose was only to hold on the spinner.

 

 

With the collet in hand measuring the ID (internal diameter) indicated the device should work but it was waaaay too loose and turning the nut did not seem to set the device. I took a pair of needle nose pliers and compressed the flutes of the collet to almost eliminate the gaps. Sliding fit!

I then proceeded to set the collet with the nut. I could not pull the assembly off the motor shaft by hand. Granted, it was not an empirical test, but at least my friend felt better that he did not have an adapter that could not work.

In a couple weeks we will have the ESC, battery, wiring completed and will spin the unit up. At least with a sailplane, tossing a prop will have less serious consequences.

-=Doug

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Permalink Reply by Stephen R Mann on January 21, 2013 at 6:47am

I know it doesn't help here, but since I discovered one motor that had lost the "C" clip holding the motor together, I always give each prop a gentle tug before flight.  Once I found a loose collett (I had just put the props back on and must have forgotten to torque one down).

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ModeratorPermalink Reply by David Anders on January 21, 2013 at 7:01am

My toolkit that I take with me keeps growing everytime I go out - Lol.  But even after triple checking everything, i'm still dying to get my hands on those tiger motors.  I know it will mean resetting everything, but there's something to be said about confidence whilst flying.

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Permalink Reply by Dan Banks on January 20, 2013 at 2:10pm

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.

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Permalink Reply by R. D. Starwalt on January 21, 2013 at 6:46am

Dan, at least you have the knowledge to recognize a defective component!  Gott sei Dank!

Until we can devise a suitable cage or 'ring prop' (been done for boats BTW), for our quads, the rotational forces exacted on the motors will continue to cause damage to our motor shafts if impacted (blade strikes).

Most of the local hobby shops in the US can get EFlite adapters in 2 or 3 days from their distributor. That depends, of course, on your location (and the shop's business attitude).

As mentioned previously, a sliding fit is preferred. What you describe with the 3.0/3.17situation is concerning. 'What's a few hundredths of a millimeter?' someone might say. A LOT when it comes to this situation.

The sketch above is NOT a sliding fit though the shaft pressed into the collet firmly. There would probably also be some scrubbing damage to the inside of the collet but that is minor compared to the bad fit.

Good thinking. Good luck and definitely let 3DR know about the eccentricity issue. They don't make the parts but their vendor should own up to the quality issue.

-=Doug

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Permalink Reply by Dan Banks on April 23, 2013 at 11:14pm

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.

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Permalink Reply by Richard Boyhan on April 24, 2013 at 4:37am

Excellent post. One question, you mention that 37mm was the best length, but did not recommend it. You mention something about a previous post. Could you explain?

You can use the following to press in and out motor shafts.

3/16 socket long
3/32 drift punch
Vise

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Permalink Reply by Dan Banks on April 24, 2013 at 7:37am

I was referring to my post two posts earlier on the page.  Basically, I think the adapters that came from 3DR with the motors are poorly designed/machined and are not suitable for use.  And if you're going to go through the trouble of changing the shafts on your motors, you might as well get new prop adapters and use whatever is the best shaft for those.

I'm going to give the bolt-on adapters a shot, and (eventually) find out what kind of damage is done when I (inevitably) whack another prop on the ground.

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Permalink Reply by Richard Boyhan on April 24, 2013 at 9:32am

I've not had any issues with loosing adapters. I've had issue with bent motor shafts. Thanks for finding replacement shafts.

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Permalink Reply by steve F11music.com on April 24, 2013 at 11:06am

I've used these in the 3DR motors with no problems.

http://www.goodluckbuy.com/replacement-3-17mm-shaft-for-brushless-o...

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Permalink Reply by Tim Green on April 24, 2013 at 8:28am

DJI 2212/920kv motors are $24 each.  They have short shafts.  Their props stay on.

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