Vibrations and folding props

I have a Spyder 700 running T-Motor U5 motors X8 with 15" props and I wondered if anybody knows what on folding props causes, or more precisely what I need to try to reduce, vibrations on the Z axis. You can see the difference between one piece and folding props in the graphs. I just love the ease of use that folding props gives you…


Z-axis vibs are usually not related to the prop balancing. Main influences are frame rigidity, boom cross-section and Pixhawk mounting style and the forward airspeed of the copter. Especially light copters runnig large props and flying fast are a very promising combination if you are looking for z-axis vibration trouble :wink:

Thanks Holger but not in this case as the frame is the same, the only change is the type of prop…

This was from today when there was a 15mph wind gusting to 20+ mph. Vibes still within tolerance but getting close…

@Peterev The Z-Axis vibrations is a very under discussed problem in copters.

@hsteinhaus is correct in that it is not usually related to balancing of the props in the usual sense.

Think of the aerodynamic effect of your props moving forward, especially at speed or in a strong wind.
Half the prop is gaining speed from the forward motion and half is losing speed (simplistic version).
So you have a twisting effect from the prop, and combine that with any other factor, as Holger mentioned, and you can setup severe vibrations, especially if it hits harmonics of your frames natural flex.

So what does this mean?
There is no one simple answer, you will have to look at the whole structure of your frame and work out where the flex, which is unavoidable, is being introduced into the frame and/or being magnified.

Folding props are a great idea but think about the most minute clearance at the hub, to allow the blades to fold, manifesting a slight twist in the blade that will cause a vibration.

Just my 2c worth.


Thanks Mike,

The only variable here are the props so I don’t believe that the frame needs investigating, it’s plenty strong enough to resist one piece props so the folders must be invoking vibes somehow…

I have tried varying the tightness of hub bolts with very little effect, the flight above was with them tight enough so that manually there no vertical movement but enough for them to fold out, perhaps I’ll try them even tighter. You can see them balance themselves at the very start of the graph.

I may statically balance them again, they were within 0.1g of each other last time.

Perhaps it’s just that they don’t have identical profiles.

I believe that the centripetal force of a prop rotating at 8,000 rpm wouldn’t allow the prop to twist but I may be wrong there. By their very nature I guess they will never be able to compete with one piece props…