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Conclusions from Round 2 of Testing and Next Steps

A project log for Goliath - A Gas Powered Quadcopter

A BIG Gas Powered Quadcopter

peter-mccloudPeter McCloud 10/19/2014 at 15:370 Comments

So Round 2 didn't conclude with a hover test, but a lot of progress has been made. The engine has been run now for a total of 3 1/2 minutes, allowing some of the design flaws to be identified and worked out (improved battery mounts and improved tensioners). The downside is that the belt system still has an oscillation occurring, but it is very much improved. For completeness, I've uploaded video of Tests #7 and #8 (see below)




So one of the culprits is the tensioner pulley on the double sided belt. It should have been a 20 mm wide pulley, but when I did the tensioner redesign, the pulleys were on back order until mid-December, so I used the 50 mm wide pulley I had leftover from the previous design. The lack of a flange on both sides could be allowing the belt to move around, causing the oscillations.

There was another lingering issue and is the pulleys I used for the idlers on the single sided belt. Again I used parts I had on hand and using toothed pulleys on the flat side of the belt isn't ideal. To remedy both pulley situations I've ordered some flat belt pulleys for the idlers and then I'll move one of the toothed pulleys to the double sided belt. If that doesn't resolve the the oscillations, the next step would be to add some belt guides to the double sided belt.

While I'm waiting for the pulleys to arrive, I'll be taking the time to incorporate the starter and ignition relays. I've decided on a dual relay board from parralax which arrived last week. I decided to omit adding a relay for the fuel solenoid, because it didn't seem like having separate control for the fuel shutoff was essential. My initial thought was the aircraft have a fuel shutoff in case of an engine fire, so Goliath should have a fuel shutoff. However, the fuel for Goliath isn't gravity fed, and If the engine is killed with the ignition, the fuel pump stops and the fuel will be cut off anyways.

The kit is pretty straight forward and it didn't take long to solder all the components together.

Once the other parts come in and the relays are incorporated, I'll repeat the same test configuration with the dummy props. Once the belts are solid then I'll add the real propellers on and do the run up.

One last thought was about weight growth. At work I deal with a lot of projects that are always weight challenged. In initially scoping out Goliath, I made conservative weight estimates to avoid all the redesign work that goes into trimming weight. However, I've added a lot of items that I hadn't initially planned for, so I weighed Goliath in it's current state. I did this by using a handheld luggage scale at the end of each of the arms and lifting up until each side was off the supports. The total weight right now is 160 lbs, 80 lbs less than the gross weight I was targeting. Ducting, controls and a tank of gas should be much less than this so for now it looks like things could come in underweight.

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