The easiest way to mount APM2 on ArduCopter.

You'll need 4 rubber rings ~1.5-2cm diameter, ( used on prop-savers ) and 4 M3x10mm Spacers.

Just squeeze it through the hole:

 and lock it on the spacer:

you can use 4 extra spacers and mount the top plate:Good flying to you all :)

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Comment by Rob_Lefebvre on January 30, 2012 at 7:17am

@Max, the CPPM signal is cool, how do you do that exactly?  My receiver can do it, but do I need to reprogram the multiplexer?  So, that helps.  But where are all your ESC wires?  Mag, GPS, Sonar, Xbee, etc.

@Helitrasher: Not even close.  You need way more damping than that.  Well, that's what I have now, but I don't think it's enough.

Comment by Ron Curry on January 30, 2012 at 11:33am

Without some sort of damping this type of mounting will oscillate at whatever the resonant frequency is determined by the tension on the o-rings and the weight of the APM2. That's why suspension on vehicles has both springs and shock absorbers. The shock absorbers serve to dampen the oscillations. Otherwise, when you hit a bump the vehicle would continue to bounce until the friction in the suspension system (which is relatively low) dampened out the cycles which would be quite a few cycles.

In the area of flybarless controllers for traditional helicopters vibration is a significant problem and most of the manufacturers have worked out recommendations for mounting although a significant number of users always tend to believe they can somehow do better - often based on "more is better" assumptions. One such FBL controller that is similar to our APM in many respects is the Skookum SK-720. It has 6DOF with 3 gyros and 3 accelerometers. For traditional helis it can be difficult to reduce vibrations enough so as to not overwhelm the accelerometers but Skookum has approached it from a simple engineering based direction and that is to use a double sided foam tape along with a metal plate to mount the SK-720. Because the the SK-720 only weighs about 25 grams it needs additional mass so that combined with the damping and isolation of the foam tape the resonant frequency of the combination of the SK-720, the plate, and the foam tape is relatively low which reduces the high frequency vibrations which can overwhelm the accelerometers and gyros.

I'm not fortunate enough to have received an APM2 yet but I have applied these concepts to APM1 with pretty good results. To protect the APM I've used clear heat shrink to encase it. I first apply some very thin servo tape to the bottom of the APM so the heat shrink is well adhered to the APM then put the heat shrink tubing on and shrink it. Here's a photo:

Here's the bottom:

Here it is mounted:

It is very secure and to remove it I use a razor blade to cut the foam and then with my thumb I can "roll" the leftover adhesive off for remounting.

As far as I can tell vibrations transmitted to the APM are quite low. Actually a really good feature would be a vibration index or "figure of merit" that users can use to determine if vibes are too high. The SK-720 has such a feature as does the Mikado VBar. Really helpful. Perhaps I'll look into writing the code.

Cheers,

Ron

Comment by Gareth Rens on January 30, 2012 at 12:13pm

Hey Ron.

Are you sure the bottom side of your magnetometer isnt touching the imu board. It looks a little close...

Comment by Ron Curry on January 30, 2012 at 12:49pm

THanks Gareth. Just checked it and it is very close but not touching so I think it's ok.

Comment by Ron Curry on January 30, 2012 at 1:03pm

One more learning from the FBL area. Cabling can be a significant conduit for vibrations from the airframe to the controller such that all the vibration isolation and dampening in the world won't help because there is a direct path through the wires to the circuit board. Therefore it's important to ensure that the wiring is of small gauge and is "dressed" such that it's loose. Adding a loop so there is flexibility and not bundling the wires tightly helps. Except for power leads I try to use #22 size or smaller for signal leads. Here's a bad photo showing the slight loop and small gauge wires on a Logo 600 with an SK720:

BTW, my comments are to imply the o-ring idea is bad. It's simple which is good. If there were some way to provide dampening it could be very effective.

Comment by Ron Curry on January 30, 2012 at 1:28pm

I intended to say: "BTW, my comments are NOT to imply the o-ring idea is bad". My apologies for the typo...

Comment by Søren Kuula on January 30, 2012 at 2:50pm

Hi,

Eeeh silly question maybe? But: I have ordered and paid for an APM2, and not received it yet. I was not worried as is says in the store it is a pre-order. But how come that some of you already have one ready to install? Dud you get an early batch, or are you developers or testers...?

Regards

Soren


Developer
Comment by Max Levine on January 31, 2012 at 2:09am

@Robert,

You can see 4 ESC wires on the right, mag and gps are on the board so no wires here :) 

how to connect ppm-sum to APM2 board (there is firmware support already)

For APM1 you'll need to update the ppm-encoder:

http://code.google.com/p/ardupilot-mega/wiki/BusPirate

http://ardupilot-mega.googlecode.com/files/ArduPPM_v0.9.87_Arducopt...

http://ardupilot-mega.googlecode.com/files/ArduPPM_v0.9.87_manual.txt

@Soren, yes its a dev-boards.

Comment by Jonathan M on February 14, 2012 at 11:31pm

Curious to see if anyone has any luck with the mounting technique for the APM 2.0.  Did it significantly reduce vibrations and vibration induced drift issues during flight?  I am hoping to spend the weekend doing some testing and analysis on vibration isolation, and this may be a candidate for testing.  However, I am worried that there is really no dampener with this method.  I would think that adding some stiff foam or vibe-gel between the o-rings and the stand-offs would at least provide some dampening in the x and y direction accels.  I could be wrong though.  Experiences?

Comment by Tomas Soedergren on February 15, 2012 at 4:47am

Jonathan,

My experiences with o-ring suspension so far are good and my APM2 3DR quad flies well even though my test flight activities has inflicted some slightly bent prop adapters (but I bought a bunch of new ones today) now inducing vibrations in the frame. If you look back you fill find a pic on my o-ring suspension.

I say you should not worry so much about lack of dampening. There is dampening in the O-ring rubber due to hysteresis related energy loss and I do believe the cable harnesses contributes as well. My advice: Just try it.

Tomas

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