Slower motors, more vibrations?

[markyoe]

I built a 450 quad with 1000kv motors and have been battling the jello effect for a while now. The frame is a DJI Flamwheel clone as many newbies, myself include, start out with. Do you think motors with a higher kv rating would create less or smaller vibrations?

Also, has anybody had any experience with Rotarbits sold on HobbyKing? I am looking into building a tricopter, any suggestions?

Thank!

 

[ZoomNBoom]

There are so many factors; props, frame, motors, controler tuning,..
The most important factor however is always prop balancing. Did you do that?
Next up is balancing motors.
However no matter how well you balance everything, you will still need to experiment with vibration isolation. Rubber balls, foam, velcro, jel pads. There is no miracle solution im afraid.

 

[Cyberdactyl]

Yep, sometimes it feels like you're dealing with chaos theory and working forever to achieve even modest spontaneous order. I've found the smaller the camera and the larger the props, the harder it is to not have jello. The larger 'buzzy' vibrations can pretty much be eliminated by balancing.

But even perfectly balanced larger props, especially if they are slow-fly cheapies, are almost impossible to get a tiny 'key-fob' size cam (Mobius) to not have some jello in some region of flight. Whenever a larger, flexible prop changes planes it will induce some flex. Hard throttle changes will make the prop cup, etc.

The smaller the camera, the less rigid the mount must be, almost to the point where the camera is hardly held, in or by, the isolation medium.

My best luck for very small cameras on larger multi's has been bubble wrap loosely wrapping the camera. For the quad below, I tried and tried and finally got a nice jello free image for a Foxtech V3 (one of the lightest cameras available, it makes the Mobius seem like a brick), but it required a rubber mounted wire suspended platform, the camera sat on silicon gel and loose foam, and ultimately sat on a bed of bubble wrap. Plus the battery on the platform helped drop the vibration frequency as well.

So yea, anyone who's tried to use an ultra small camera on a larger multi and get good video has been there.

 

[PHugger]

I think Jello has something to do with the frequency of the vibration being close to the refresh rate of your CMOS sensor. Slower motor (larger props) may mean different vibration frequencies. CMOS sensors scan the chip and build the image line by line. This can cause jello or ripping if the image moves during the scan. CCD on the other hand reads the whole chip in one shot. The Mobius has a CMOS sensor. This isn't necessarily bad (most all DSLRs use CMOS), but it does present some problems with video. So back to the problem at hand: as Cyber and Zoom have said - Eliminate the vibrations and change the frequency. There are a million different ways to isolate and reduce vibrations, but as Cyber stated, weight is your friend. It will change the resonant frequency of your setup. Of course you don't want to add weight to your rig, but moving stuff around can have a big impact.

My Fortis Tricopter has a "clean" camera platform/sub-frame. It is attached to the rest of the frame with Tygon tubing (length probably has some effect). I also attach the battery to this frame section. the increased mass will change the resonant frequency and make it harder for vibrations (from the "dirty" part of the frame) to move the camera around. I hold the camera on with rubber bands and seat it on some moon gel. The last two tricks may or may not have any effect, but I'm sticking with them. The results are quite good.

Here is a short test video on my Fortis Tricopter shot with a Mobius (normal lens).

I realize that a smaller racing quad is not the same - they are not designed as AP platforms. Trying to get a small 250 size racer to hold your camera without vibration is not gonna be easy. Size, Mass, and Balance all need to be tamed to work in your favor. Even your 450 quad is probably quite stiff. My tricopter has 16" booms and 10" props. The video above is shot with unbalanced, well used Gemfans. I never balanced them as I was tuning and crashing a lot at first. Ever since I put these on, I haven't broken any (kinda dinged up though). I am running RCManChild motors that were never checked or balanced (I assume they are good quality and didn't need it).


Best regards,
PCH

 

[markyoe]

Thank you for the suggestions. I think I will create a suspended platform beneath the quad that will carry the Mobius and the battery. I have balanced my props but not my motors. How do you balance a motor? Any suggestions as to a tricopter frame? I think it would be fun to learn how to build one.

 

[PHugger]

I believe there is an FT video on using a laser to balance motors.
I've also seen video using a smart phone and vibration app.

Basically you attach either your phone or a laser to the arm that the motor is on.
You spin it up and check the vibration. The phone will give you a number.
The laser will move a dot around on your wall.
Apply tape to the bell in a systematic manner to minimize the vibration.
When the vibrations are at a minimum (this is fairly crude) you are done.
Search YT for tutorials.

The cream of the crop for Tricopters IMHO would either be a Fortis or an RCExplorer (David the Swede).
Fortis advertises on the main FT page. They have great service and available spare parts.
RCExplorer ships out of Sweden and is often on backorder.
David has a new frame with an integrated Naze in the Frame plate that looks nice.
The Fortis also come in a Y6 configuration (heavy duty AP).
I believe the FT Electrohub can be used to make a Tri (they used to have a Batbone frame).
I'm not sure about the new AnyCopter frame.



Best regards,
PCH