zebulonfilms
Member
So I have had the 10-15 foot drop when I engage altitude hold with rev r3 like some others, and while I look forward to the update that fixes it, I was experimenting to see why some people have the drop and others don't:
For me, it appears to be vibration related.
I'm using Avroto 2814's, Graupner 11x5's, 2x 5000maH 4s (10,000maH), carbon arms, 800mm MTM diameter, and AUW with GH2 camera and Gaui Crane III gimbal of about 4000g. Main gain and attitude gains at around 30 on my JR x9303.
I have been balancing props with the top-flight magnetic balancer (I have the dubro but the friction of the wheels I felt was too much to get an accurate balance). I though I was doing everything well, but noticed when I would spin up that the main craft would jiggle on spin up and then settle as the props got up to speed. Apparently that means there is still a balance problem even though my footage was looking fine.
I found two problems:
The magnetic balancer itself was out of balance. I would balance a prop perfectly, including shaving down the hub so it would remain stationary in any position. Then on a whim I pulled back the hub holders and rotated the prop about the balance shaft 180 degrees, and presto, I was out of balance again. So the hubs and/or the shaft was out of balance. I bought another balancer, same thing. I rolled the balancer shaft on glass, it seemed ok. I tried just spinning the shaft and hubs on the balancer and sure enough, the hubs where unbalanced. I tried marking them and shaving them down, but the mass it so light that I couldn't really nail it, but I got it closer. I bought the Great planes fingertip balancer and modded the Top Flight unit to hold the shorter shaft, hoping it would be better. It was much better, but still off. After grinding the screw on hubs down more I got it pretty close, but still the mass is so low that it's hard to get a consistent spin. So after lots of trial and error, I rebalanced all the props, occasionally turing the prop 180 on the balancer to see where I was at, trying the guess the error caused by the out of balance shaft/hubs.
Second discovery: the Avroto prop shafts are not quite 6mm. With the Graupner 8mm-6mm sleeves, I happened to notice before I tightened down the nuts this time that the prop would slide the tiniest bit horizontally on the shaft. I applied a non-overlapping piece of scotch tape on the shaft and although not quite thick enough to take out all the slop, it was at least closer to being centered. (I verified later that this free play would put my painstakingly balanced prop out of balance). I previously used the APC props and the plastic prop adapter was slightly smaller than 6mm and would stretch on the Avroto shaft, so I had never considered this before.
Since I couldn't fully trust the prop balancer, and the motor bells could still be contributing, I verified and further tweaked the balance on each individual motor/prop using the "bounce the laser off the mirror attached to the end of the motor arm and watch the dot on the wall as you spin up each motor individually" method. The dot would move the most at relatively low RPM's on an unbalanced set, then as I increased the RPM's the dot would settle back down as gyroscopic forces took over. (Hence the wobble as I spun up the craft). So I would use that low RPM level to see where I was at. Many test tape applications later, I got all 6 motors to not move the dot at any RPM. (only one bell and two props needed tape)
I replaced all the Avroto bearings with Boca Abec5 hybrids. One of the new bearings was bad from the factory, when I was doing the laser test I could feel one of the motors when spin up would send a vibration through the frame. One benefit I guess of spinning each motor/prop up independently.
So after all of that, I went for a test flight, no other gains changed or any other parameters. Alt hold gain was at "6" still. Went up high, switched on Alt hold and kept my finger on it preparing to disengage if there was a drop, and low and behold no drop at all, stayed right there.
At this point I'm guessing I could raise my main gains, but I'll wait until after my shoot tomorrow. So lesson learned: If your ship wobbles at all on spin up, you may have some more balance issues to work out.
The end result for me besides a working Alt hold, is that my footage looks even sharper!
For me, it appears to be vibration related.
I'm using Avroto 2814's, Graupner 11x5's, 2x 5000maH 4s (10,000maH), carbon arms, 800mm MTM diameter, and AUW with GH2 camera and Gaui Crane III gimbal of about 4000g. Main gain and attitude gains at around 30 on my JR x9303.
I have been balancing props with the top-flight magnetic balancer (I have the dubro but the friction of the wheels I felt was too much to get an accurate balance). I though I was doing everything well, but noticed when I would spin up that the main craft would jiggle on spin up and then settle as the props got up to speed. Apparently that means there is still a balance problem even though my footage was looking fine.
I found two problems:
The magnetic balancer itself was out of balance. I would balance a prop perfectly, including shaving down the hub so it would remain stationary in any position. Then on a whim I pulled back the hub holders and rotated the prop about the balance shaft 180 degrees, and presto, I was out of balance again. So the hubs and/or the shaft was out of balance. I bought another balancer, same thing. I rolled the balancer shaft on glass, it seemed ok. I tried just spinning the shaft and hubs on the balancer and sure enough, the hubs where unbalanced. I tried marking them and shaving them down, but the mass it so light that I couldn't really nail it, but I got it closer. I bought the Great planes fingertip balancer and modded the Top Flight unit to hold the shorter shaft, hoping it would be better. It was much better, but still off. After grinding the screw on hubs down more I got it pretty close, but still the mass is so low that it's hard to get a consistent spin. So after lots of trial and error, I rebalanced all the props, occasionally turing the prop 180 on the balancer to see where I was at, trying the guess the error caused by the out of balance shaft/hubs.
Second discovery: the Avroto prop shafts are not quite 6mm. With the Graupner 8mm-6mm sleeves, I happened to notice before I tightened down the nuts this time that the prop would slide the tiniest bit horizontally on the shaft. I applied a non-overlapping piece of scotch tape on the shaft and although not quite thick enough to take out all the slop, it was at least closer to being centered. (I verified later that this free play would put my painstakingly balanced prop out of balance). I previously used the APC props and the plastic prop adapter was slightly smaller than 6mm and would stretch on the Avroto shaft, so I had never considered this before.
Since I couldn't fully trust the prop balancer, and the motor bells could still be contributing, I verified and further tweaked the balance on each individual motor/prop using the "bounce the laser off the mirror attached to the end of the motor arm and watch the dot on the wall as you spin up each motor individually" method. The dot would move the most at relatively low RPM's on an unbalanced set, then as I increased the RPM's the dot would settle back down as gyroscopic forces took over. (Hence the wobble as I spun up the craft). So I would use that low RPM level to see where I was at. Many test tape applications later, I got all 6 motors to not move the dot at any RPM. (only one bell and two props needed tape)
I replaced all the Avroto bearings with Boca Abec5 hybrids. One of the new bearings was bad from the factory, when I was doing the laser test I could feel one of the motors when spin up would send a vibration through the frame. One benefit I guess of spinning each motor/prop up independently.
So after all of that, I went for a test flight, no other gains changed or any other parameters. Alt hold gain was at "6" still. Went up high, switched on Alt hold and kept my finger on it preparing to disengage if there was a drop, and low and behold no drop at all, stayed right there.
At this point I'm guessing I could raise my main gains, but I'll wait until after my shoot tomorrow. So lesson learned: If your ship wobbles at all on spin up, you may have some more balance issues to work out.
The end result for me besides a working Alt hold, is that my footage looks even sharper!
