Custom quad anti-vibration frame

[Pyrofer]

I had a kit X650 frame and it flew well until I crashed and bent a motor shaft.

My best efforts have not straightened it enough to stop some bad vibration when throttle is high, so I get messed up sensor readings and it crashes to the ground in a wobble of death.

The solution (was actually order new motors, which are on the way) was to build a new frame.

The new frame had 2 alu box tubes instead of 4, a notch was cut out of each and they slot together to form a cross. A bolt in the middle holds them together.
This means the central plates don't have to hold the stress and strain of the motor arms.
Instead of screwing the plates down to the arms, I used rubber grommets to insulate the plates/bolts from the arms and rubber washers on the top of the plate to keep the metal bolt away from the top/bottom plates.
Only 4 bolts are used (there were 8 previously to hold the arms straight) so vibration is pretty well stopped right there. I went further and used rubber washers between the motor brackets and the arms too.

The end result is that vibration reaching the center plate is greatly reduced even with the bent motor shaft and the sensors are now stable again.I also took the opportunity to move the power section to the underside including escs to move it all away from the magnetometer and removed the interference problem I had there too.

All in all, a very successful frame, when the new motors arrive it should be rock solid, but for now its very flyable compared to the wobble of death I had before.





These three images show early construction so you can see the washers and grommets. I will upload finished pictures soon.

The grommets and washers work wonders on vibration reduction and I recommend anybody making a frame considers this.

Finished Quad here,
http://www.flickr.com/photos/pyrofer/7182491548/sizes/l/in/photostream/

[UndCon]

If you cut half way through each boom you also create a very weak spot. unless you support it on the outside.

I've had crashes that bent alu booms exactly where bolt holes are located several times.

I also found out recently on a Tricopter and a Quadcopter that it is more effective to mount boards and sensors more rigid than using thicker foam.

In my latest builds I use a sandwich design

--paris v4 board--
--hot glue--
--coroplast--
--hot glue--
--alu frame--


//UndCon

[krst]

yes, as other have said to counter the vibrations you also need some mass coupled to the board. Vibration dampening the board only which is a few gram is nearly impossible... But your way is nice as i guess you plan to put all the electronics on that middle main frame. Good vibration dampening material which is easy to find is EAR ear plugs used in compression, EAR also sells more fancy stuff but that is more expensive

[Pyrofer]

The frame works but I am not sure it was worth the effort. It seems small vibration is ok but the larger vibration from a faulty motor is still a problem.
As far as weakness?
I had a large gust of wind cause a very high altitude drop and crash with the frame slamming into the ground almost completely sideways (90degrees to level) and nothing broke.
The frame shows no signs of being in a crash, the motor plates at the end took a bit of a bruising but I guess the main thing was it was grass it crashed into. I am therefor not worried about the strength of the frame.

I am more worried about the crappy motors I bought that turned up with dodgy bearings and caused more vibration than anything else.

[krst]

yes engine and prop vibrations can be nasty and should be kept minimum... and again as the mass is low of the electronics they cant cope with the large vibration and dissepate them. I have been thinking alot about how the vibrations depends on frame and engine size, i a only have very small experience and have very small frames and engines ~130 gram and manage to get very good stabilitiy. I would suggest that the keeping the engine weight as low as possible to the frame also as that means a lower rotational mass etc...

[Pyrofer]

Other than the battery as much as possible is on the top plate to keep the mass there. The hope was the rubber grommets/washers would absorb it before it got to the top plate but there is so much its not possible.
When I get decent motors I assume it will all be lovely.
ie, solution is to remove the vibration at source not to try and decouple from it.