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The Model
Part 1 - Chassis
Part 2 - Tail
Part 3 - U/Carriage
Part 4 - Servos
Part 5 - Electrics
Part 6 - Flight Trials
Part 7 - Assembly
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Analysis
 
        

 

Scratch Built Collective Pitch - Hummingbird / Hornet Hybrid

Part 4 - Servos

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This model will have the servos lying in a horizontal plane, again to keep the helicopter as low profile as possible. The servos are arranged around the mainshaft at 120' angles apart with the pitch servo at the rear. The pitch servo has its arm running parallel to the lenght of the chassis.

I began by drawing one servo to scale, arraying this around a central point then drawing the servoplate from this allowing clearances for correct servo movement etc.

 
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To check the principal I mocked up a servoplate from copper faced veroboard which is light, strong and easily worked.

This was used during flight trials before making the final version in carbon fibre.

 
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As usual I started out by printing off a template from the 2D drawing and temporarily fixing in place with spraymount.

Note the rear centre mark which will be used to fix the plate in position.

 
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Using a dremel the servoplate was first cut to shape then finised via filing.

As I am using very small servos the servoplate itself is quite small measuring less than 50mm in width and length.

Note the hole for the mainshaft and for the fixing screw which is countersunk to recieve an countersunk head M3 machine screw.

 
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With the servos fixed in postion the servoplate is barely visible.

The servos themselves were removed and replaced many times during flight trials to reposition servo arms for fine tuning etc. Use a tape that is strong enough to hold the servos but easily removed until using something more permanent once position is finalised.

Note that I am using ballraced swashplate links, these are far better then the stock links.

 
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The whole assembly is then fixed in place to the top chassis rail with an M3 machine screw and a small amount of CA along the top edge of the chassis rail.

I have also added a small collar slid down over the main mast and CA'ed in position.

Done in this way the servoplate fixing gives a good deal of mutual strength to the junction of the main mast and chassis rail.