gimbal for spot trace GPS tracker

Last crawled date: 1 year, 11 months ago

This is a gimbal for a Spot Trace GPS tracker. I made it at NK Labs for a high-altitude balloon launch. It is printed here in SLA Formlabs Grey Resin on a Form 2. There are two versions here. The second was made to reduce weight. It is untested. Some of the photos showing assembly were done in Formlabs Clear Resin.

There are 3 concentric circular frames which can rotate about 2 axes. The hexagonal recess are for M3 nuts. The GPS mount is screwed to the center frame. The GPS is placed in the mount with logo side in. The GPS is kept in the proper orientation by gravity. There is a clamping plate to help you attach to your payload. There is an optional battery frame allowing for tight integration of the battery and gimbal. This allowed for better battery and gimbal positioning for better balance.

Clamping plates are 40mmX50mmX6mm. The clamping plate holes are a loose 3.75mm diameter 15mm x 30mm apart with a 90 degree countersink. The mounting faces (clamps removed) are 156mm apart. The diameter of the outer ring is 152mm.

The weight with GPS installed and screws is about 280 grams without the battery frame.

Battery frame adds 29mm to the height with a 40mmx114mm footprint. Hole spacing is 98mm x 15mm. It can straddle a 71mm x 25mm battery. It adds about 60 grams of mass.

Assemble and use at your own risk. For any launch, look up and follow your local regulations. And give NK Labs a shout out.

BOM

Spot Trace + subscription service (about 91grams without the mount)

From McMaster:
12 - M3 nuts (McMaster-Carr 90591A250)
4 or 8 - M3 screws (flat head, 14mm + clamp attachment width rounded up [you can probably over size by up to 5mm]) (14mm + 1/4in ~=20mm McMaster-Carr 92125A136)
4 - M3 screws (socket cap, 8mm) (McMaster-Carr 91292A112)
4 - nylon spacer, 1/8" long (McMaster-Carr 94639A701) (you can alternatively print the spacers)
6 inches of 1/16in steel rod - (McMaster-Carr 8888K171)
8 - 1/16in push on nuts (McMaster-Carr 94807A015)
super glue (I used Gorilla Super Glue Gel)(optional)


To Print (we used a Form 2 SLA printer with Grey v4 resin, note that support material could double the needed volume of material):
1 inner circle(35mL)
1 middle circle(26mL)
1 outer circle (57mL)
4 spacers (you can alternatively buy the spacers) (0.1mL ea) (I printed extras)
1 or 2 clamp plates (11mL ea)

Optional Battery Frame Accessory:
battery frame (33mL),
+4 M3 nuts,
+1 clamp plate,
4 battery attachment screws (12mm M3 Flathead McMaster-Carr 92125A132)


Tools:
diagonal cutter for hard wire (Knipex 70 01 160)
1/16in drill bit (McMaster-Carr 29115A711)
pin vice (McMaster-Carr 8455A12)
push on tool (McMaster Carr has one ) (I used the hole in the center of dremel collet wrench ) (if I were going to make a lot of these, I could imagine making a jig for a press or pliers wrench)
file/sandpaper
2 mm allen key (for flat head screws) (McMaster-Carr 7813A43)
2.5mm allen keys (for socket cap screws) (McMaster-Carr 7813A44)


Assembly instructions:
1. Inspect and clean up the 3D printed parts. If you printed the spacers, make sure the top and bottom are smooth, flat and parallel.
2. Using the 1/16” drill bit in the pin vice, clean up 1/16” holes by running the 1/16” drill bit through them a few times.
3. Super glue M3 nuts into hexagonal holes being careful not to glue yourself or the threads. 4. Wearing gloves, I like to use a long screw with a nut on the end, add the glue and the pull the nut into the hole so it seats properly. (If I were designing this again, I’d likely move to brass inserts. )
5. Cut 6 in of rod into four - 1.5in sections using diagonal cutters. Roll your sections across a flat surface to inspecting for straightness.
6. Push push-on nut just onto the end of each rod using push-on nut tool (or an appropriate size hole [3.3mm or ⅛” ] in piece of metal) and trim excess (It is a bit tricky. You may want to put something in the way so you don’t push it on too far)
7. Slide the rod with push-on nut through the inner ring, spacer, middle ring.
8. Push on another push-on nut being careful not to squeeze the parts (causing friction). (Maybe use something you can pull out as a spacer)
9. Repeat on the opposite side. Repeat for the outer and middle ring.
10. Screw GPS mount to center ring.
11. Charge GPS and turn it on.
12. Snap in the GPS on mount, logo facing in.
13. Mount completed gimbal to battery base (optional).
14. Mount the assembly onto the payload.

After running with this I made a quick lighter weight version in case we needed to launch again. In the future I think it would be fun FEA exercise to optimize for weight and durability.

Lighter-weight replacement parts:
1 inner circle lighter (13mL)
1 middle circle lighter (22mL)
1 outer circle lighter (25mL)
battery frame lighter (30mL)

This version is a little smaller and mounted from only one side. Without the battery frame, approximately 130mm height clearance is needed. In the other frames 125mm (off center) - 135 (centered)

The weight of the lighter assembly with GPS installed and no battery frame is about 180 grams.

The smaller version is a little trickier to put together. It remains untested.