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I made an electric skateboard (it works great, goes about 25mph) and the motor takes 4 screws to mount it. Motor is mounted to a 1/4 piece of aluminum. The screws go right into the motor and don't come out the other side so bolts are not possible. Over time that crazy vibration (from the road and pebbles and little potholes, from the motor itself being pretty powerful) being makes the screws come loose. Usually happens in less than an hour.

I've tried the strongest loctite but nothing seems to hold the screws in place. The loctite lasts a little longer but still they come loose. I have a Ryobi drill that I tightened it with. Maybe I am using the loctite wrong. I am very new to building stuff that is meant to be used in a more extreme way. In a way where lots of vibration is happening and things are moving very fast. And where you life may depend on it. Plus if loctite is so permanent than how would I be able to fix it if things went wrong? And if I use a less permanent loctite then would it even stay for this type of vibration?

I am well aware that building something this crazy is a good way to get hurt, but I really enjoy learning. I would love to learn how to make something that lasts for years and doesn't come loose. Something that is "skookum".

How do you tighten screws to aluminum that will vibrate a lot and get them to not rattle loose over time.

Motor is here. See BLDC-108.

Here is a diagram of the motor. It does not have the sliding brackets as pictured. It came without those, for some reason.

enter image description here

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  • $\begingroup$ If this is not a general question can you specify the motor model and maybe a photo or drawing? In general you'd first try to get rid of the vibration (by changing tyres or using some dampers for the motor?) but if you still have vibrations you can use best practices, like locking the screws, etc. a drawing of your motor, shaft and chassis would be perfect to receive practical and applicable ideas. $\endgroup$
    – Gürkan Çetin
    Jun 25 '17 at 12:51
  • $\begingroup$ @alephzero I updated my question. It does not have those slots for the heat sink as in the diagram. For some reason it doesn't come with it. But that is a great idea. $\endgroup$
    – Johnston
    Jun 25 '17 at 15:05
  • $\begingroup$ Beware of using a heatsink for mounting. Heatsinks are very often not structurally connected to the main device. $\endgroup$
    – Laurence Payne
    Jun 9 '18 at 11:59
  • $\begingroup$ I have never had one loosen that was properly tightened in the first place and had lock washers , if designed for lock washers. $\endgroup$
    – blacksmith37
    Jan 8 '21 at 15:55
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There are several ways you might try to fix this, for example.

  1. Don't use screws. Put some studs into the screw holes in the motor and fix them permanently (like the studs that hold the wheels onto a car). Then you can attach the studs to the mounting plate (or the skateboard frame) with nuts and shakeproof washers.

  2. Ignore the screw fixings, and run long bolts along the 8 slots in the motor heatsink. You will need to make another plate for the back of the to motor, attached to the skateboard somehow. (The OP added a comment saying the motor does not have the slots shown in the picture, but I'll leave this idea in the answer because it might be useful to somebody else).

  3. Design something so the motor can "vibrate" along with the wheel, and absorb the vibration somewhere else - for example bolt the mounting plate to the board with spring-loaded bolts. (That is similar to option 1, but not using studs).

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  • $\begingroup$ Good answer suggesting the studs. I'd also add reduction of vibration, as it's unwanted also for the person on the skate. $\endgroup$
    – Gürkan Çetin
    Jun 25 '17 at 16:27
  • $\begingroup$ " I'd also add reduction of vibration" - that was the main idea of option 3. You can't eliminate the wheel vibration that comes from the ground surface, but you can "decouple" it from the board itself. Presumably an expensive board might have some vibration damping already designed into the wheel suspension system. $\endgroup$
    – alephzero
    Jun 25 '17 at 17:22
  • $\begingroup$ Well, of course eliminating vibration from the motor is desirable. But eliminating it from the complete skateboard (with soft tyres, etc) was my main intention. Of course if the root problem is not solvable, component level solution would be required. $\endgroup$
    – Gürkan Çetin
    Jun 25 '17 at 18:13
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The loctite is only good for one kind of rootcause. Please try the loctite + spring washer combo. If it is still loose, use 2 pcs spring washer.

These should do the job.

Or worst case use mechanical fixation washer with a lip what is possible to bend on the nut side.

I hope this help. Br.: Peter

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"split lock" spring washers are nearly worthless for serious torque or vibration. Belleville type lock washers are better, especially if serrated.

The best by far, amazing actually, at least for resisting torque (but not length changes) are the nord-lok. They are expensive.

If the screw is very long and there is thermal expansion or you are concerned more about the screw head rising due to length changes, vs random torques, then actual helical springs are sometimes used -- need sufficiently stiff ones.

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  • $\begingroup$ I second Nord-Lock. When you need them, they work fabulously well. $\endgroup$
    – achrn
    Jan 9 '21 at 15:31
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There are two options to improve the vibrations and keep that motor attached. The first would be to isolate the motor with dampeners, but that doesn't eliminate the vibration from the road. The other option that is used extensive in aviation is to use fasteners that can be safety wried. Here is a video to explain safety wiring. This company has some aircraft grade hardware including some screws that are drilled for safety wiring. The company is Aircraft Spruce. You can also get safety wire from that company. Good luck!

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Best way to go about this situation is to use thread loctite. There is special one for threads. This will keep away from vibration!!

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