Sensor mounting

Vital to the quality of our control loop is the ratio between useful signal and noise of our sensor units. Unfortunately this ratio will be greatly influenced by the vibration level on our heli.

To undrestand this please note that all SMM/MEMS sensors are micro-mechanical parts that will be taken into oszillations. From differencies between the taken and the real achieved oscillations our sensor electronic will be able to caclulate a rotation rate.

Unfortunately our sensor doesn't know which diffrence is cused by rate and which by vibrations and will measure the whole differencies as rate for our VStabi.

Of course vstabi has some filterings to avoid unsenseful signals but this filters have its limits also. In this case it will be the modelers part to take care for a vibration-free running helicopter. In fact every rotating thing on a helicopter can effect vibrations and must be analyzed accordingly to the flight behaviour.

How will vibration inputs be shown?
- As first you may note a drift on one or more axis. You have to steer against it always to keep the heli in position. Additional vibrations can be shown as small servo movements without stick inputs. The heli mayhave a lightly indifferent and not precise flight behaviour. Additional some "waves" on the rotor disk while hovering can be noticed also.

If you will have such a effect you should always search for the reasons and debug it. This has minor priority before doing any other things.

For a cause study you should always run the heli with its flight headspeed and feel on the frames with your finger for vibrations. Additional to this you can use the VStabi pc soft and watch the integral values on the live panel. A vibration drift will be shown here in its effect to our control loops.

A senseful vibration analyzis can be done as follows:


  • Motor and adjustment (nitro, gas), fuel, glow, muffler ....
  • Main blades / tail blades including tracking in flight
  • If necessary balance blades
  • Bladeholder spindle check (remove 1 blade, rotate spindle with a hexdrive)
  • Remove all blades, run and check system on the bench
  • Remove main rotor, run and check system on the bench
  • Remove tail rotor, run and check system on the bench
  • Remove motor pinion, run and check system on the bench
  • Check again with different headspeed

Pleas note that vibrations can be caused by out of balance running parts as spindles, shafts, gears and also ball bearings!

What can we do if we couldn't manage to get rid of those vibrations?

Ok, in this case ther will be nothing left as to be sure that our sensor will get as less as possible vibrations. Therfore we normally use the enclosed tape. If you will see vibrations now you have to figure out which fitting of our sensor will be best in this case on this heli with its own and special vibration profile.

That means nothing els than testing different tapes. Please take into consideration that multiple layers of tape maybe cause a escalating sensor. So use only one pad but different thickness and stiffness.

If you won'get a good running system with this things it will be time to play out our last ace. We increase the sensor mass using a metal plate with about 3mm thicknsee with a thin stiff tape on teh sensor bottom. Then we fit the complete unit with the original tape on our heli.