Goddam HK bearings..... I've been racking up some serious flight time with my Tricopter over the last month (several hours a week). Funny thing is I was going to mount the gopro today, but I thought I'd do a warm up flight with the cheap action cam..... I took it for a warm up spin, was only in the air for 30 seconds, I was trying out my latest config of the 32 bit gimbal controller and suddenly it flips over and hits the deck. Luckily it was only 5m up at the time, no damage to the frame besides one broken 3mm nylon bolt, couple of zip ties, one less than smoot DT750, all CF and electronics in tact. After careful review of the flight footage and review of damaged parts I have come to the conclusion that it was again the front left motor that died, this is the same location as the previous one that died for the same reason. It is down to either the bearings or a failure in the 11x4.7 propeller hub.
Whats funny is I expected this for when I switched to 4s as the DT750's are only 3s rated (but many run them at 4s without any issues and without changing the bearings), whats funny is I'm yet to change over yet, although they have had a 10 min test at 4s..... So it's possible it was damaged then.
I cannot wait for my emax motors to arrive - why did I choose the slow option!! Hopefully not too much longer before I get some quality motors on it. Since I return to work on Wednesday I'll be doing a quick rebuild with a spare motor (DT750) this afternoon and will convert to 4s and be flying again with it tomorrow. Luckily I have some spare bearings for the DT750's so I can get the dodgy one working again.....
My reasoning behind it is that all parts were found within 10cm of the frame. It flipped to it's left on the footage, indicating loss of lift or a weight shift to that side. I could see that the arm which the nylon bolt broke speared into the ground, the motor came off the mount but was still connected by two cables, I think the 3rd cable is due to impact damage, the small bolt end with nut and the head were next to each other. The propeller was nearby in two parts, a split at the hub. I think due to the propeller being that location and the split on the hub indicates it occurred when the motor speared the ground while spinning. The gimbal also had partly separated, 3 of 4 rubber balls had come out of the top plate the 4th came out of the bottom plate. The left motor is harder to turn than normal, leading me to believe the bearings are not in a good shape. Only other possibility was that the gimbal bottom plate fell off swinging to that side, but the footage doesn't back that up, in fact the gimbal tried to stabilise the camera on the initial failure.
So it was either bad bearings, or bad propeller which has now damaged the motor....
Oh well more rebuilding...... Lucky I find that part as much fun as flying.
Chris