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Double Sided Belt Added, First Full Throttle Test

A project log for Goliath - A Gas Powered Quadcopter

A BIG Gas Powered Quadcopter

peter-mccloudPeter McCloud 02/16/2015 at 18:433 Comments

It's officially been a year now since I started putting together Goliath (2/14/15) and I got to start this year out well by doing more testing.

Since the last tests I've ordered and installed the new 30 mm wide double sided belt and installed the new pulleys for it. I've also relocated and redesigned the tensioner for the double sided belt (pulley and tensioner layout). This was to put it in the proper location to take up the slack that develops in the belt.

Relocating this was what took the longest amount of time. I was trying to mirror what I did on the single belt side, but due to the structural layout there isn't as much room and ran into packaging issues. ( I know it's a 10' quadcopter, I really shouldn't have those, but I did)

Here's a top view of the single sided tensioner. The center beams angle away from the tensioner.

Here's the top view of the double sided tensioner. The center beams angle towards the tensioner. The made it hard to find a good location at the right angle to mount the springs too. Additionally, I didn't have room for the larger springs so I initially downsized the springs.

Once that was in place I finally got to testing. Since the single sided belt testing went well I went straight to testing with the flight props. Here's the video with Tests 17, 18 & 19.

Test 17 went well, but the double sided belts were still seeing a bit of oscillation. I figured this was due to the smaller springs being used. Below is a picture of the different springs I've been using, and the smallest one is the one I used for Test 17. They were shorter and didn't have enough travel to take up all of the slack developing. So for Test 18 I re-arranged the pulleys to get the medium sized springs in the tensioner.

Test 18 definitely showed an improvement to the belts, but I still thought it could be better. I then spent the better part of the day re-arranging pulleys and adding another pulley to allow the tensioner to fit the largest spring. These are the same ones I use on the single sided belt.

So that finally did the trick. For Test 19, Goliath started up and at quarter throttle ran smoothly. After a few seconds to verify that everything was running smoothly, I gave it full throttle.....and Goliath didn't hover....

The great news is that it didn't fly apart. The belts oscillated a bit as it came up to speed, but damped back out at full throttle. The propellers held together as well.

So why didn't it hover?

Short answer, I need more data. Weight is a likely culprit, more hardware was added than anticipated to get the drive system working. Power is another possibility, it could be that the engine isn't providing the required power.

Next step is to get a good weight measurement and add tachometers to determine what RPM the system is achieving. Looking closely at the video there does seem to be some settling as I set it back to 1/4 throttle, so I think I'm getting close.

Discussions

zakqwy wrote 02/17/2015 at 15:39 point

Nice write-up! You're transferring a lot of power between pulleys--definitely a design challenge. Good to hear the oscillation is under control. Excited to see more performance testing results.

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suicidal.banana wrote 02/16/2015 at 21:51 point

Great update, nice to see you've overcome the oscillating issues :D

One thing i was thinking you may wanna consider is to level out the propellers vertically, so they all sit at the top of the arm, while there's no reason you cant overcome their height offset with coding, you'd get a more stable flight if you solve it in hardware.

Keep them updates comming!

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Peter McCloud wrote 02/16/2015 at 23:30 point

Thanks!
Yeah I'd like to get all of the props leveled out ( it bother's me aesthetically, but practical reasons are good too )  My original plan was to add spacers, but that was with 20 mm wide belts.  With the wider belts and main pulley I'd need spacers over 2" tall.  It'd easier to make them all the same height if I modified the design to use shafts instead of axles, then it'd be easier to separate the pulley from the propellers. More things to think about :)

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