Tricopter shaking without props

[TheFinder]

I've been working on my first tricopter build and I'm looking for a little advice. Without props it starts shaking pretty bad on the ground. No flights yet. Is that normal or is there something wrong with the setup? I've run through the basic kk2 setup but no balancing. I've heard of balancing motors but I didn't know if it was a necessary step. Thanks!

Here is a video of the shaking
http://tinypic.com/r/6f40h2/5

 

[Craftydan]

It's not needed if the motors are close to balanced, but with that kind of shimmy, you might need to.

First, I'd check each motor to see if one is the source of the shake or if all three are contributing -- if it's just one, you might have a defective motor.

If it's all three, one at a time, you'll need to balance the vibe out of them.

 

[Cyberdactyl]

That is very indicative of extreme servo jitter.

Go to 'miscellaneous settings' and at the bottom you'll see 'Servo filter'.

See what the number is. If it's ~55 or lower, that might be the culprit. Start at 70 and work up until it just goes away, but don't go much past 95 or you'll lose all servo function.

I have my tri, which is the exact same size as yours set at 85.

 

[Craftydan]

See?!?! that's what I get for not building a tri!

. . . one more multirotor I need to slap together . . .

 

[TheFinder]

I set servo filtering to 90 and it almost eliminated the vibrations. Still some vibrations at certain angles of the yaw motor and when I power down. I'll try balancing the rear motor and see if that helps. Any other tips for removing vibrations? Thanks!

That is very indicative of extreme servo jitter.

Go to 'miscellaneous settings' and at the bottom you'll see 'Servo filter'.

See what the number is. If it's ~55 or lower, that might be the culprit. Start at 70 and work up until it just goes away, but don't go much past 95 or you'll lose all servo function.

I have my tri, which is the exact same size as yours set at 85.

 

[Mustang7302]

I dont believe it to be a motor balance issue. It is still servo jitter. Either servo just isn't a solid enough quality to hold position well or there is noise in the signal. Also make sure it is moving the right direction. When you give left yaw the motor should tilt to the right when viewed from the back. If it is backwards it could be the KK2 giving usual input trying to make corrections.

Above all, get it in the air. Sitting on the ground the KK2 cannot do its job.

 

[Cyberdactyl]

I set servo filtering to 90 and it almost eliminated the vibrations. Still some vibrations at certain angles of the yaw motor and when I power down. I'll try balancing the rear motor and see if that helps. Any other tips for removing vibrations? Thanks!

Other than balancing the prop and possibly the motor's bell, try and insure the yaw mechanism has as little play or slop as possible without binding. DON'T mount the motor on a vibration isolation medium like a sheet of rubber or stiff foam.

 

[crlock]

VERY IMPORTANT check if your servo is digital or analog, i had massive servo jitter, servo filtering didn't helped, finally discovered that my servo was analog, KK2 and analog servos don't mix. get a digital servo and you'll be ok.

 

[TheFinder]

Other than balancing the prop and possibly the motor's bell, try and insure the yaw mechanism has as little play or slop as possible without binding. DON'T mount the motor on a vibration isolation medium like a sheet of rubber or stiff foam.

The yaw mechanism does have a little slop in it so I'll try building another.

 

[TheFinder]

VERY IMPORTANT check if your servo is digital or analog, i had massive servo jitter, servo filtering didn't helped, finally discovered that my servo was analog, KK2 and analog servos don't mix. get a digital servo and you'll be ok.

The servo is digital but I accidentally cut one of the wires so I had to resolder it back together. Maybe the soldered wire is causing noise? I figured digital wouldn't have that problem.

 

[Cyberdactyl]

I have tried both the BMS-385DMAX Digital and the analog Turnigy 380MAX.

The digital Bluebird works really well, very smooth, nice fidelity, but it was back in late spring when I was new to my tri and I was worried of crashing and stripping a $20 servo, so I put the $15 380MAX (I know, makes little sense) on and have never taken it off. It works very well. It's maybe 80-90% as smooth as the digital. I have a very small, almost non-existent amount of jitter with it set at 80-85, but it's so minor, it doesn't bother me or really effect the flight characteristics.

 

[TheFinder]

I have tried both the BMS-385DMAX Digital and the analog Turnigy 380MAX.

The digital Bluebird works really well, very smooth, nice fidelity, but it was back in late spring when I was new to my tri and I was worried of crashing and stripping a $20 servo, so I put the $15 380MAX (I know, makes little sense) on and have never taken it off. It works very well. It's maybe 80-90% as smooth as the digital. I have a very small, almost non-existent amount of jitter with it set at 80-85, but it's so minor, it doesn't bother me or really effect the flight characteristics.

That 380 max looks like a good one. I was in the same situation as you and picked up the D-MG16 as a spare. I was able to get the bluebird later and haven't tried out the D-MG16. Do you know how much torque is needed for a tricopter servo? The D-MG16 has 2.9k not sure if that is enough.

 

[Cyberdactyl]

I would think 2.9kg is fine. Especially if you're flipping around a 9" or 10" prop. I have seen smaller servos on tricopters.

Mine is direct drive. It's the David W tri 'steering mount' config. There's a thread at rcgroups with literally dozens of designs. For the life of me, can't figure out why people fret and toil over such complicated yaw mechanisms, unless they are experimenting. If you want a dirt cheap, easy, strong, and fast to build mechanism, David's design is the ticket.