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Still holding together, getting ready to make more rotors

A project log for EVPR: Electric Variable Pitch Rotor

An electrically actuated variable pitch rotor with a wireless interface

peter-mccloudPeter McCloud 08/20/2017 at 22:490 Comments

Updated design

After the first successful (success == not flying apart) rotor test last week, the design was tweaked to change the orientation of the servos so that the centrifugal force held the internal gears in place instead of tearing them out. The change required moving the axle gear, and a new set of hub plates were cut  with the gear pockets moved. Below is a shot of the reassembled hub with the reversed servo orientation.

Rotor weight

The rebuild of the rotor allowed the opportunity to weigh the EVPR by itself (versus attached to the hub). The complete assembly weighs 2.7 lbs (note: in the future I still need to add the alternator, but the batteries give about 10 mins of run time right now). The fixed pitch rotors weighed 1.25 lbs, so adding variable pitch only adds. 1.45 lbs, better than I'd anticipated (The 7075 aluminum axles reduced the weight considerably). For a full set of 4 rotors the total increase in weight will only be 5.8 lbs.

In contrast, the grid fins control concept is anticipated to weigh 6 lbs a piece (not including actuators and mounting hardware. A set of 4 would add 24 lbs of weight. If the variable pitch rotors perform as hoped, that will mean upwards to 18 lbs of weight savings.

More Testing

With the rotor rebuilt, two more tests were conducted. Both tests were 60 seconds long and the rotor held together. Both blades have survived 3 start-up/shut-down cycles and 3 minutes of run time. It's looking like the mechanical bugs have mostly been worked out.

More Rotors

With the hardware performing well, the prize money from the Wings, Wheels and Walkers round was invested in buying enough parts to build a full set of variable pitch rotors. The majority of the hardware is from Servocity.com and the parts arrived on Friday.

I've been really happy with their hardware so far and if you send them pictures of your project, you can get a discount. It's also pretty cool to get a handwritten note with your order!

 Forward Work

More testing needs to be done on the first rotor to build up the time and cycles on the hardware to make sure things will hold up in the long term. The other big priority is to to mature the firmware and demonstrate controlling the servos.

As time allows, the buildup of the second rotor will continue. The hub plates have already been cut and the rotor blades are almost complete. Work on the build instructions have started now that the hardware has reached a somewhat stable state.

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