Hi all. Trying to tune in my APM 2.0 with V3 firmware for Alt Hold for a customer on my custom, folding, 400-size quadcopter. She oscillates (vertically), then gently starts dropping until it lands.

I've tried some of the tuning tips, and reduced the oscillations, but she still drops. Any hints folks?

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Log a flight and compare GPS relative Alt to BaroAlt.

It's also possible that the prop-wash is affecting your barometer since it's so small and the props are so close to and above your APM.

Good idea to check, Scott. And if you have some log files, then that is an easy one to check. But I was having a similar response, and found that I had to set THR_MID. the default is for the 3dr quad.

@Owen: what is your batt/motor/prop setup? if it is different from the 3dr by some amount, then you need to adjust the THR_MID parameter. 

randy outlines this procedure here, but in essence:

You can do this by flying in stabilize, and just focus on getting a good stable hover in for a few minutes. Then land, open up the .log from this flight, and graph the "THR IN" parameter that can be found in the "CTUN" message/row. you should see some nice flat plateaus from your hovering. read that value (or the average, it will obvious vary a small amount).

In the full parameter list, there is a parameter titled "THR_MID" (list is alphabetic) change its value to the value you read from your hover, write parameters and go try it.

Unrelated: I tried the different colored props, too to try to provide some orientation clues while flying. I found the havings the different colors left/right actually allowed me to get orientation even when the copter was flying L/R across my view. the problem with F/B that I found was that if the copter is pointed to your left or right, and it rolls, it can be hard to see which orientation is front. TL;DR, I found L/R colors to be more helpful.

Thanks Scott, I too wondered if the proximity of the props may be playing a part. I'll have a look at the logs. Thanks for your response.

Thanks for your response Ted, I'll go through those recommendations and see if I can fix it. Good point about the L/R prop colouring too, I only really struggle though when I don't have the GoPro on to determine the front of the craft. Normally I have LED's mounted too in aviation/nautical layout, Red, Green, White etc which helps a lot.

My motors are NTM 1200Kv from HK, with Plush turnigy 20amps, and 8x4.5 props. I'm running 4S , 3300mAh too.

thanks again.

FYI: I have a small quad using the exact same motor/battery combo and 8x4.5 carbon props.  On that one I had to turn THR_MID down to 400 for good loiter/alt-hold behavior. (I'm using 20A blue series ESCs flashed with SimonK firmware). All other settings are stock except I turned the main KP_RATE down just a bit or else it was too "twitchy" once I fitted the CF props. It's got a couple hundred flights on it with no incidents after I replaced all of the crappy stock motor bearings with Align helicopter replacement parts.

 

 

Yea, I had to turn my 650 size quad down to ~350. I guess its a lil overpowered.

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