Rocket Mk.III

By Sconeboy on Nov 17, 2019

4  131  2

My very last build on the ARX-R V1 frame, due it it no longer being available. It's fragile, but it's insanely fast. First few flights were capped at 85% throttle, even so it reached a top speed of 155mph. Will test 100% throttle once it's undergone some tuning, hoping to reach 180mph or more. Currently running Betaflight 4.1 with RPM filtering, blackbox logs look very clean so far. All speed readings are from the GPS, which if I remember correctly has ~3% margin of error for speed readings.

The battery mounting is very unusual. It is held in place by the camera/GPS cage, and is stabilized by 4 claws, and two large o-rings. Having the battery upright helps reduce drag which is the greatest enemy of speed builds. Eventually I plan to add 3d printed fairings to help squeeze out a little more speed, assuming the ESC survives that long. I haven't gotten the current sensor dialed in yet but it will easily pull 120+ amps at full throttle. I'm going to try several ~1300mAh 6s packs until I find one that can somewhat handle the current draw, I'm open to suggestions!

Having four 470μF caps is probably overkill, but they weigh very little and I figured running 2400kV motors on 6s with aggressive props would generate a fair bit of noise. I got the idea from the RC car world where some speed builds will have huge capacitor banks to help filter voltage ripple. No idea if the same idea applies to quads but I definitely have a noise free video feed.

Flying this thing is crazy. The combination of 70° uptilt and the camera being so far away from the COG makes it handle very strangely. The lights are for landing it LOS because the frame is fragile, and it lands on four standoffs attached to the stack. No way I can land this quad softly through my goggles with that much uptilt. My DVR is broken so I'm going to have a buddy record a flight for me. I'll post a link to it here hopefully within a week or so.

Update: 164mph top speed so far, still tuning.



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Rc Exp   Nov 18, 2019  

bruh at the speeds these things go, does it even have aerodynamic stability?

Sconeboy   Nov 20, 2019 

idea, but no oscillations so far so I'm happy with it.

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