Hi guys,
Had a few queries regarding how I mounted my APM (mainly since I get a compassmot of 0%!). Well here it is. This will only work on side exit APM's!
Step 1:
Screw in  4 x 8mm risers in to the bottom plate, and add one sheet of moongel on top of the core (if you have no core, superglue some risers in the spot. Note: yes, that's moon gel stuck into the FPV camera slots.

Step 2:
Glue a 1mm fibre plate on top of the risers & two drops on the moon gel of the core. You can superglue the whole thing in place, but I chose to use 2 screws, for additional security. I use a battery tray plate from a spare set of quadframe legs.

Step 3:
Add you vibe solution. I've use moongel with good success, but I've decided to try out zeal corners (which i why I dismantled it)

Step 4:
Carefully place the APM in place. Take care to ensure nothing it binding; you don't want vibrations transmitted to the APM via the wires. Insert the battery to make sure it does not press the "out" servo leads. Also try and make sure the "in" servo cables don't torque the board too much, but this can be tricky.

Step 5:
Screw it all back together, but take not of the front starboard mount. This is where and how I placed the DJI riser. It's not exactly over the 4 holes - it only uses 2, This moves it outboard a few mm. Not much, but it might be this detail that separates a 0% compassmot from a 1%...


...take a look at where the USB port is.... You can still reach it with the standard USB cable, by pushing through the port front leg...but it's a really, really tricky, and you are in danger of pulling out a solder!

So find a USB cable with a 90' bend in it. And when you find one...let me know...before the logs fill up and I crash!

Views: 6574

Comment by Muhammad Al-Rawi on September 8, 2013 at 2:34pm

Very nice setup.

Think you could get to your USB with this?

Comment by Brad Cameron on September 8, 2013 at 4:03pm

wow that is fantastic good work!
very detailed info as well!
(plus your disco looks absolutely amazing)

Comment by Brian K on September 8, 2013 at 5:29pm

Oh this is awesome.  I just put a Disco together not even 3 days ago.  Currently running with the APM mounted on the top but I was brainstorming solutions for mounting it inside (once my external GPS/mag unit shows up).

What are your vibe levels?

Any issues with mounting the APM so far ahead of the CoG?

Comment by Chris Riccio on September 8, 2013 at 5:47pm

If you really can't find anything, just hack up a en existing 90 degree micro USB extender like this. 


Comment by Dave on September 8, 2013 at 6:17pm

Excellent write up. I have my APM mounted in the exact same spot as you with the same problem for USB access. I ended up getting a few cheap USB cables from Monoprice. http://www.monoprice.com/products/product.asp?c_id=103&cp_id=10... This one has a small head that I can feed through the arm hole and holding the APM with one finger I can guide it in. The plan is to leave it plugged in at all times and just shorten the cable by cutting out 2 feet leaving the female end to sit on top. Its not high on my priority list, still working on PID settings. 

Comment by Rana on September 8, 2013 at 6:38pm

For a good magnetic interference isolation, external Mag has to be at least 30cm higher to the plane of rotating BL motors, yours seems quite low. 

Comment by Chris Riccio on September 8, 2013 at 6:53pm


I disagree. I'm still using an APM 2.5 on a standard DJI F450 frame with my APM mounted on the top plate > Zeal > RV Anti-Vid mount > Zeal > APM and I get a 28% compassmot score and wonderful loiter/waypoint performance. I've said it once and I'll say it again. Stop looking at the numbers and just go out and FLY, you'll be surprised. 

Comment by Brian K on September 8, 2013 at 7:05pm

Rana: Euan already stated that his compassmot value is 0%.  Is that not good magnetic isolation??

30cm is almost a foot.  Is there anyone mounting their external mag sensor a foot above their vehicles?

Comment by Rana on September 8, 2013 at 8:13pm

Chris & Brian, I won't be much adamant on my emphasis but would say that that were my findings. For a 550 or 600 or more size quad, external mag is really not required. Motors with large dia cause higher interference as compared with that of lower dia one's. I made my first quad at very early time when even at DIY drones, only few people were aware what Quad is.

However I myself did so many flights with APM1 and APM2 with on-board mag and had not observed much appreciable interference till I had a serious crash during, later I came to know that my quad was fooled of direction of north and rather coming to me it moved to some other direction and crashed into the tree. After that I did so many hit and trials of different size quad frames and then finally raising the magnetometer height. For this I got inspiration from DJI however here at DIY Drones people were still using on-board mags. Reason of interference in my crash case was, one of the motor was taking comparatively high current which caused high magnetic flux.    

After raising the external mag to aprox 1 feet, I did not meet any crash due to direction fooled ;)

Comment by Euan Ramsay on September 8, 2013 at 10:19pm

Cheers guys! I'll look at these USB options today.

@ Brian: My vibe levels are good with moongel - +/-1 when loitering in slight breeze...+/-5 when pushing it around with full sticks in stabilize. I've not tried acro, but I suspect you'll exceed the recommended maximum of +/- 5. But since I never fly acro, that's ok for me!

I took this apart to try out the zeal squares; they are definitely more secure (when you consider the USB problem), and they are better in heat. I will let you know my vibe scores in the next flight. I will be re-running compassmot (since I've moved wires etc) while it's raining and I can't fly!

Re: CoG - Mounting the APM this far forward wasn't really that much of a problem, as it's not really that heavy - the problem was the battery. A 5000 3S is heavy, and it needs to be "right in" for good CoG. So by necessity you need to push the APM forward to allow the battery to move forward.


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