Tuesday, November 26, 2013

QUADframe Battery Tray

battery tray on QUADframe Pro Six

One of the goals of our hexacopter is long flight times.  Our hex is large and relatively heavy (3.3 kg without batteries) so that requires large batteries.  We planned to fly with either three 6S 8,000 mAh batteries or two 6S 10,000 mAh batteries.  These batteries are large and heavy.  QUADframe sells a battery tray that mounts between the arms.  Unfortunately those mounts are designed for much smaller batteries.  Time to design a new battery mount.

QUADframe battery tray

After some playing around with the frame and batteries, I determined the best place to mount them was over the center plates of the frame.  I removed the protective dome and decided to mount the plate on the four standoffs that supported the dome.  I wanted to make the tray out of honeycomb carbon fiber.  Unfortunately I didn't have any left and I didn't want to wait to order it.  So I made my own carbon fiber laminate.  I epoxied some thin carbon fiber sheet I had to both sides of some good quality 1/8" plywood.  I clamped it in a vise between some boards as it dried.  The next day I cut it to size on a wet tile saw with a diamond blade.  Sorry, I forgot to take pictures as I made the laminate.

over-sized plate attached

Next I marked and drilled the holes to mount the tray.  The GPS mount that I made was in the way of the tray.  So I cut a groove in the tray for the GPS support.  Had I known the batteries were going there, I would have mounted the GPS somewhere else.  With that done I mounted the tray and tested the fit of the batteries.  The tray was longer than needed, so I cut it to the same width as the center plates of the frame.

screwed to standoff

To hold the batteries in place I used some heavy duty Velcro tape and Velcro straps.  I cut a slot in the tray to pass the straps through.  The standoffs were higher than needed so I cut about 1/2" off of each to bring the center of gravity down.

finished tray on frame

The tray is very strong; doesn't even budge with over 6 kg of batteries on it.  As a bonus, it also protects the flight control systems from crashes.  The 10,000 mAh batteries mount front to back, while the longer 8,000 mAh batteries mount lengthwise.

10,000 mAh batteries

8,000 mAh batteries
Even with all of that weight on top, the hex flies pretty well.  The 8,000 mAh setup balances slightly better because the third battery mounts below the hex on the landing gear (see first photo).  At some point in the future I may move the GPS mount so I can move the 10,000 mAh batteries closer to the center of the hex.  But for now, it works.

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