Optical sensor 4

[SHAGGY1505]

Hi, I am looking at designing a piece of equipment that will reduce the vibration in a small scale RC Helicopter. For this I am looking to measure the phase of the helicopter and the dc motor I will be using as the shaker. To then ensure the motor is 180 degrees out of phase with the helicopter. The question I have is how will I design a circuit to utilise an optical sensor to collect phase information of the helicopter and then the dc motor? Thank you in advance for your input

 

[3DDave]

There are throttle matching systems for gas powered R/C airplanes so that one engine is kept at the same RPM as the other. The setup could be set so the pick-ups are 180 out of phase if you wanted that.

 

[WKTaylor]

Shaggy1505... In addition to 3DDave's comments...

The following 'Duhhhh lesson learned' is an important element in aircraft vibration...

In the 1980s I worked on several propeller driven Vietnam era aircraft. We were constantly dispositioning repairs for odd/annoying cracks, chafing/galling, etc.

During the examination of one aircraft [OV-10A] for a 'slow climb-rate problem' it became evident that the variable pitch prop-blade pitch settings [for each blade] and blade-tip-tracks were out-of-tolerance. The defective prop assys were replaced and the 'newly overhauled assys' were precision evaluated/re-adjusted for matching-everything: blade pitch, variable pitch synchronization, blade-tip-track and [Duhhhh] dynamic [on-engine] balance.

We also discretely 'sanded'* the top-coat paint finish on the spinners, wings, booms and stabilizers to attain a much smoother appearance... since the paint was noticeably grainy/rough all-over [to the touch]. Although the sanded aircraft looked 'odd' [to say the lest] the results were a much 'smoother' skin surface texture.

[* using jitter-bug sander with fine-weave Scotch-Brite pads and a ‘light-touch by the mechanics’... HOWEVER, we didn’t touch the paint on balanced control surfaces]

The results of this evaluation, adjustments and maintenance actions were like a lightning-bolt hitting us engineers and the maintenance team squarely in the brain!

Critical attention to these static/dynamic elements made for [instantly] one of the 'smoothest-running-fastest-climbing aircraft' in the fleet. It was more than evident that attention to these 'small static/dynamic details' had an amazing effect on the entire aircraft: performance and vibration-wise.

We took this lesson to heart. All fleets of prop aircraft were re-examined in-light-of-these lessons-learned on this one aircraft. The maintainers and flight crews noted a vast reduction in damage/discomfort and an improvement in the quality of ‘everything else’: flight-performance improvements, reduced noise/vibration, diminished structures/systems problems, etc.

Regards, Wil Taylor

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[Kwan]

Thanks for the information Wil! As usual you bring additional detail due to your vast knowledge. I do appreciate you input to this community.

 

[SHAGGY1505]

Although an interesting post Mr Taylor I’m not sure what help this is to my original question/problem?

 

[MikeHalloran]

Shaggy, I think the point was that you might spend some time trying to static-balance the pieces of the helicopter to reduce the imbalance, before trying to compensate for the imbalance in flight.

I also wonder if the simple eccentric spinning around one axis, even if you can get it exactly phased, will be able to counterbalance the helicopter's motion, which may not be a simple planar sinusoid.

Maybe you could fly a recorder and a six-channel accelerometer first, to get a handle on the problem you are facing, before trying to develop an automatic system to compensate for the problem.


Mike Halloran
Pembroke Pines, FL, USA

 

[IRstuff]

Perhaps it would be better to elucidate what your end requirements are. How low a vibration are you trying to achieve?

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