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Not So Rapid Prototyping

A project log for Goliath - A Gas Powered Quadcopter

A BIG Gas Powered Quadcopter

peter-mccloudPeter McCloud 08/08/2014 at 15:452 Comments

I haven't been posting build updates as frequently because the build activities have mostly consisted of sanding....lots and lots of sanding.  The good news is that I'm nearly complete with the first flight quality propeller!  I've talked previously about everything up to adding resin to the propeller so now I'll talk about the finishing process.

My early attempts at vacuum bagging used saran wrap over the fiberglass/resin and breather cloth over that before everything is placed inside the bag.  That was the propeller where the blade ended up twisting.  The other thing that went wrong with that earlier propeller was that the breather cloth left an uneven imprint on the surface.  For the first flight quality propeller, I omitted the breather cloth since there wasn't too much excess resin.

The results were significantly better, but I should have worked the wrinkles out of the bag better.  The wrinkles fill with excess resin that eventually needed to be sanded off.  After curing the next step was to start finishing the propeller.  I placed it back onto the CNC router using the alignment holes and re-drilled the mounting holes, as well as an alignment hole in the center.  The center alignment hole was used to drill out the center with an hole saw.  The center hole allows the shaft and nut to pass through.  I didn't cut the center hole with the router because it had a hard time cutting through fiberglass.  I probably could have just cut it a lot slower, but it's easier to just use the hole saw.

After that the the excess at the tips was trimmed off and the trailing edge was marked off and cut off with some shears.  You can see the excess resin in both these pictures.  A Dremel was used to start the smoothing process by remove the bigger pieces. Then it was time to sand (being sure not to sand into the fiberglass) and then add primer.

The sand/primer process was repeated several times.  The second propeller didn't need as much since I did a better job of removing the wrinkles.  Here are the first two props in various stages of sanding...

While the first one needs just a little more sanding and a final coat of paint, I wanted to see how much it weighed thus far:

I was quite surprised that the propeller only weighs 1 lb, 3 oz.  I had assumed a much more conservative weight for the propellers, so that'll help get the vehicle weight down.  If I make another set I'll probably add more reinforcement.

I've also started on getting the props ready to mount.  I removed one of the shafts from the vehicle and replaced the bushing bolts with longer 4" bolts that the props will mount to.

Then I testing out the hole alignment and bolted the prop to the bushing.  The only thing left it to make a crush plate to help distribute the load over the prop.

I'll be posting more often over the coming weeks as I get closer to finishing the props, getting ready for a hover test and completing the entry requirements for The Hackaday Prize deadline!

Discussions

Steve Shaffer wrote 08/08/2014 at 18:10 point
very nice work! care to share the CNC gcode and bit/settings?

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Peter McCloud wrote 08/09/2014 at 02:40 point
I've got all of the g-code available on the Goliath Github repository https://github.com/mccloudaero/goliath-quadcopter. I'm still working on writing up all the details.

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