How to: Fit a Helicommand HC3-SX in a Trex 450L

[taosgraveyard]

To fit a Helicommand HC-SX on the gyro tray of a Trex 450L Dominator requires a modification of the HC-3SX case. The HC-3SX is about 2mm too wide to fit, and the gyro tray is a not quite long enough. Here are some pohotos that show how I got this to work, and work quite well.

Fortunately, the corners of the case of the HC3-SX has these knobs. We will have to modify only two of these corners, the two forward ones, to get the HC3-SX case to fit between the frame sides. This modification also works for the 450 Trex Sport, so that the HC unit can be mounted under the tray under the tail boom. On the 450 PRO, using the KDE Aluminum anti rotation bracket/gyro mount provides plenty of area (in terms of length) for the HC case, so its not an issue. For the Trex Pro, width is not an issue since the HC case is not between the frame sides.

I used a dremel cut off wheel to get started, and finished with a flat diamond file



after this modification, the HC can be made to fit between the frames







The other issue is that the gyro tray is a little too short for the HC case. I decided to glue a longer and thicker tray over the stock one, using black shoe goo.





the tray needs to be 3.35 mm by 4.5 cm. I made it slightly wider then trimmed the edges gradually with coarse emery paper, until the fit was perfect.








this is the stock tray




my tray is made from 3mm thick carbon fiber sheet, I wanted it to be rigid, since it hangs off the end a bit. I glued it down with shoe goo, so the glue on the edges is not so permanent as epoxy would be. The new tray can be easily removed when repairs are necessary.



now the HC case is ready to be mounted to the new tray... You dont want the HC too close to the anti rotation bracket, or the elevator rod will get in your FLB servo wires. About 1/2" back from the bracket seems to work well . Even though the rear end of the new tray is unspupported, since the tray is 3mm thick and is glued along its bottom (to the stock tray) and both edges (to the frame sides) I don't believe vibration will be an issue. The HC is remarkably resistant to vibrations anyway.

ALso, consider that now that there is a vibration resistant thin layer of resilient shoe goo that separates the new tray from the frame sides and the old tray... considering this new vib absorbent layer, and the fact that the new tray is 3mm thick,I think vibes should definitely be LESS than using the stock tray alone.

[bj660raptor]

Nice thread for those that like the hc. Great will you post pics of it all wired up?

[DominicD]

Why not just cut away the frames in the back, they don't serve any purpose.

[taosgraveyard]

Originally Posted by DominicD

Why not just cut away the frames in the back, they don't serve any purpose.

I did not like the way that would look.

And having trimmed an HC case to fit in a Trex sport, ( attached to the bottom of the receiver mount under the tail boom, where there is no option to trim the frame ) I already knew how fast a diamond file will file aluminum. . The filing too less than 5 minutes, I would say