Troubleshooting problems: HMB-235

Multirotor, RC

During my flights over the past week or so I have noticed some weird problems with my quad. It had issues with sudden uncommanded yaw and pitch and it just didn’t fly very nicely. It was time to fix that!

The problem with the quad was that when I suddenly throttled up, the quad would suddenly yaw the right and pitch down. Sometimes it would cause the quad to spin out of control and crash, as seen in these 2 example video’s:

Not only did the quad spin out of control at full throttle punchouts, but it wasn’t stable in fast 180’s and other sudden movements. I had the feeling I was constantly fighting the quad to keep it in the air.

The first things I tried was changing props and playing around with the PID’s, but nothing seemed to help. Luckily the SPRacingF3 board I’m using has 8MB of onboard storage for Blackbox logs. Looking at the blackbox logs showed that each time the crash or flipout happened, the backright motor was being maxed out. It seemed like it was still giving some thrust, but not enough to keep the quad stable.

Also thanks to Joshua Bardwell for including my blackbox logs in one of his blacbox analysis livestreams, go to 1:24:56 to see the part where he analyses the problem:

BTW: Joshua Bardwell has some excellent blackbox analysis video’s on his channel, go check it out if you want to learn how to interpret blackbox logs.

So the problem was clearly the backright motor, so I replaced that with a fresh one. Unfortunately that didn’t solve the problem, the quad didn’t completely spin out of control anymore, but it still had the yaw/pitch problems and still didn’t fly very smoothly. So next up was the ESC, I replaced it with a new one thinking that had to be it.
Unfortunately it didn’t change a single thing, the quad still flew exactly the same…

By this time I had done quite a bit of reading and had asked around for some advice on RCGroups and Facebook. The conclusion was that the Afro ESC’s I was using were probably causing the problem. They are using an ‘old’ Atmel chip to control the ESC and are simly not up to the task of properly controlling the powerful motors that miniquads these days tend to use.

When I bought my ESC’s, I din’t know about what was good and what wasn’t. So it’s time to get some new ESC’s. After looking at the excellent ESC comparison charts at MiniQuadTestBench, I decided to get the XRotor 20A’s, they seem to perform really well, have good QC and are able to power much motors with even higher KV’s then mine without problems. The downside is that they don’t come with BLheli preloaded (you have to manually flash it on there using an arduino) and that they are a bit bulkier then some other alternatives. My quad is already a bit chubby, so those extra grams won’t be too much of an issue for me.

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