I am using carbon fiber props and am having problems getting the nuts tight enough on the motors. I stripped two bolts today trying to get them tight enough so I couldn't spin the prop under the 'tight' nut. Is it OK to be able to spin the prop a little under a tight nut if you twist hard? Does anyone use a torque wrench and if so what torque do you use?
I use a Hitachi electric screwdriver with it set to 13, but that's for APC props. I based that on being able to pull a prop tip with about 4-5 pounds of lateral force before it moves....so not so tight that it crushes the hub. Andy.
What units is 13? .. or is that just a wrench setting, not a torque setting. So you can spin your props a little if you try hard?
It's just a setting on the Hitachi -- not a setting in torque I'm afraid. I can indeed spin the props if I'm determined to do so -- but it takes a determined about of force -- as I say, I'd estimate it to be 5 pounds lateral force, maybe 10.... Andy.
Tyler you may find that you will need to add some additional spacers on top of that standard chamfered one that comes with the motor. The Carbon blades are so thin that with the standard prop shaft not being threaded its full length that there is no way to tighten the nut without that additional washer/spacers in place.
Thanks. I looked and there is thread on the bolt all the way down to the prop even before the standard chamfered washer is put on. Once the chamfered washer is on there is a good 2-3 mm of thread below the nut so I don't think running out of thread is the problem. I think the aluminum bolts are just so fragile. Last night in bed I thought of a good test - Once I get replacement bolts I'll purchase a torque wrench and tighten various nuts to various different settings. Then I'll mark where the prop lines up on each nut to see if any move in flight and find what the limits are for too tight (stripping danger) and too loose (prop slips in flight)
Tyler consider buying a Hitachi DB 3DL2 electric screwdriver. That's what Andy was mentioning. One of the best tools that I have. Makes putting the nuts on and off very quick. You can set the torque on it based on what piece you are tightening. Andy uses a 13 setting for his props. I found that the nylocs I have need it to be at full. I hold the motor and when I can't hold it as I run the driver I am done. With a socket wrech or single wrench I used to simply tighten until firm. Kind of scientific like the instructions they give you for putting on an oil filter, tighten until firm . The prop should not turn easily when correctly tightened. It might still turn with enough force while holding the motor bell but that's ok in my book.
Thanks. I'll certainly check out that screwdriver. I've found a couple places here that sell them. I'd still like to know proper tightening torques though.. perhaps I'll buy both that screwdriver and a torque wrench and find out what setting 13 is and see how accurate setting 13 is from nut to nut. The problem with the 'that feels about right' method is that what feels about right changes from day to day and as I've already experienced, what felt about right stripped two bolts. I even stripped one and knew it and went on to the second thinking - I've got go use less torque.. but still enough and yep, stripped again.
I bought a torque wrench today and it looks like I am tightening the prop nuts to around 6nm. Some were a touch looser so it is nice to know they are all the right/same tightness now. It will also now be easy to double check that the nuts are tight out in the field by using the wrench.
Hi Tyler: Did you buy the metric torque wrench on-line? If so, do you happen to have a URL that you could share? Thanks Andy.
I bought the torque wrench in a store here in Norway but it is very similar to this one on Amazon This is the exact one I purchase in the store in Norway I went with a bike torque wrench as the ones made for mechanics are usually very large.
Thanks, Tyler. I think for the folks in the USA, it might mean that we need to buy a torque wrench like this with a 1/4 hex fitting and set the props to 4.4 ft/lbs (6 newton/meters) http://www.amazon.com/2-24Nm-Bicycl...1369289242&sr=1-9&keywords=torque+wrench+1/4" The socket for this might be something like: http://www.amazon.com/gp/product/B0076HKPQO/ref=oh_details_o05_s00_i00 The torque setting will vary for different prop types, of course.
The one I bought, and the wrench I linked to on Amazon also have a 1/4" fitting. I think it is a universal standard - at least in Norway which is totally on the metric system, I've never seen anything other than the 1/4", 1/2" socket fittings. --- edit.. or were perhaps referring to getting a wrench that was in ft/lbs instead of nm
Hi Tyler: How strange that 1/4" is standard on metric fittings....I never would have expected that. I was only suggesting the Imperial standard wrench because I thought the socket you mentioned would be metric. Good to know! Thanks Andy.
Hi guys, I looked in to it and it turned out that it's the alu hub thread that are the weakest spot. I spin 5mm prop nuts and the max force you should put on to that is 3,7 nm. If you spin 6mm prop mount - it's 6,1 nm. Cheers Bo
Try chasing a M5 or M6 (as applicable) die down the thread to extend it just enough, it will eliminate the need for additional spacers with the carbon props. Just make sure you use some cutting lubricant in the process. Then will have no problems tightening down the carbon props.