Advice needed on mounting GPS on TRex 500

I’ve at last got my mRo R15 board and GPS working (the R15 was broken when received, but mRo fixed it without question) and am at the point where I want to mount them on my TRex 500 fbl heli. The R15 is in mRo’s printed case, and I intend to mount it at the rear of the port side frame with 3M tape, with the arrow facing forwards. I’ve already set AHRS_ORIENTATION to 20, for 270 degrees roll, and checked out that it’s working correctly.

So my question now is, where is the best place to mount the mRo SAM GPS module? One logical place would seem to be the mounting block for the boom struts and the horizontal fin, but is that too far away from the centre of the heli? I’m thinking it might be best to use a second mounting block closer to the frame, but far enough away that the tail servo doesn’t influence it. That way my 270mm connection lead will reach :wink:

A related question is, the GPS module has an arrow on it which I presume should face forwards, but its socket for the connection to the R15 is at the opposite end, so it needs to double back on itself. Not a big deal, but untidy. Can the compass in the module (which I intend to use as primary) be configured 180 degrees rotated, so I can have the socket facing towards the R15 board?

You can mount the compass with a different orientation.

Ah yes, I had seen that, but assumed it was only for internal compasses.

Anyway, I’ve now seen a picture, in another forum, of a setup which has the GPS mounted just above the boom mounting block, in which case my GPS can go right way round with only a relatively short lead needed to reach the R15.

Would I be right in thinking that it’s best to use one internal compass with the external, provided they’re not showing any variance error?

You can try using the internal compass with the external but in most cases, the internal will need to be turned off using the COMPASS_USE parameter. I only use the external compass in my heli’s.


OK, I would have thought that using two would give an extra layer of security and/or precision. But I’ll stay with the external one only, if that’s what’s recommended.