One of the differences between APM 2.0 and APM 2.5 is that on APM 2.5 there is no daughterboard covering the barometric pressure sensor. So what? Well, if you've got your APM 2.5 in an enclosure of some sort, it's no big deal (the official enclosures will be out in a few weeks and will be included with APM 2.5 orders then; people who have received an APM 2.5 already are entitled to a free enclosure with their next order). But if you don't have have your APM 2.5 in an enclosure, the lack of daughterboard protecting the baro sensor from the windstream can wreck havoc with your altitude measurement!
I learned this the hard way this morning, when I mounted my new APM 2.5 on the top of my quad, out in the breeze. When I switched on Altitude Hold mode, it decided to head straight for the skies. A quick switch to manual to land, then an upload of logs to the dev team revealed the problem (thanks to Jason Short and Pat Hickey). The vortex from my props was generating crazy readings with baro sensor. (This hadn't caused a problem on APM 2.0 because the daughterboard served as a wind shield.)
Solution: a bit of cotton padding, taped on top of the sensor, as shown above. Back to air and all was well-rock-solid Alt Hold. Whew.
So if you've got your APM 2.5 mounted out in the open, like I did, tape on a bit of cotton padding or a bit of paper tissue for now, until you get a proper enclosure. And remember: pressure sensors are, well, sensitive to pressure ;-) That includes wind of any sort. Shield your sensors!
Comments
I put a band aid over the sensor. Works great !
Hi Chris,
Just following up on the enclosures for those of us with APM 2.5. Have they officially come out yet?
"the official enclosures will be out in a few weeks and will be included with APM 2.5 orders then; people who have received an APM 2.5 already are entitled to a free enclosure with their next order" - 29 August 2012.
Good info--I just ordered and received 2 APM 2.5s. So if I understand correctly, I can get 2 enclosures free of charge (ones designed for the 2.5)?
Roger, good point. It's just temporary until the new enclosures arrive. I'll be careful when I pull it off!
I used to tape defective report paperwork to circuit boards about 25 years ago. Then one night, I was pulling off the tape when the lights went out. Never again. It looked like a lightning show. The lesson is that scotch tape can be an awesome static electricity generator.
Using scotch tape on top of a circuit board is dangerous to the health of the electronics (depending on humidity and such)! If you never pull it off, it may be OK. Maybe some large black heat shrink might work>
Just to try to stay on topic here, I can tell you that you need to pad the baro even with an enclosure (yes if you cut a bit your APM2.0 enclosure will fit over the 2.5, just need new hole for GPS on side)
It does really make a nice difference with the pad over the baro inside the case. Guess "wind" still enter quite a lot in the case and influence the baro.
Man twitter sucks, just a bunch of jibberish trying to figure out what you're talking about. I have no idea what you're talking about.
My 3DRQ went together OK. The holes coulda/shoulda been about 0.2-0.3mm larger to aid assembly, but I got 'em in . If they want help doing some GD&T and possibly gauges, let me know, I'm pretty good at that stuff.
I meant the holes in the board. I see they have some sort of copper ring around them, but looks like there's some room to open the holes? I get that it works fine how it is, but being a mech. eng. that sort of thing bugs me. ;) Can't believe they made that mistake!
Robert: No, they're threaded. But it's no big deal. The frame is rigid enough with just half the screws used.
Holy cow, the screws don't go into the holes?! Could you just drill the holes in the board out a bit?
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