A lot of my free time has gone into Project Bacchus lately. Some friends and I decided to try and get a picture of the edge of space in late November, and we’ve been working at it ever since. A few weeks ago, we had our first successful flight, Bacchus III.
We’re now getting a little more ambitious, and working on engineering things a little better. We captured a bunch of pictures, but our camera stopped right after this one:
This is the field Bacchus III landed in. Taken on the way down, literally seconds before impact: talk about good timing! It landed surprisingly gently, and all the equipment survived intact. In fact, our styrofoam cooler doesn’t even have a dent from the impact. It was, quite frankly, a perfect landing. Despite this, the camera suddenly stopped after the above photo. Our conclusion is that the batteries came “loose”: the springs that hold the AAs in place inside the camera were compressed by touchdown. This disconnected power for an instant, resetting the camera.
So, we’re now very interested in battery holders. So interested, in fact, that I spent an hour the other evening playing “Consumer Reports for Near-Space Hackers.” Andy (of the eSATA help) purchased some candidate holders from Jameco, our neighborhood electronics warehouse.
Here’s my notes, if you’re in the market for battery holders.
Jameco 216152: 4-AA, 1×4, no case, $1.15/unit
This is a boring 4-AA holder, like you had in the bottom of R/C cars as a kid, yadda yadda. Except that it doesn’t have a door, like your cars always did.
The springs feel good, pretty firm. A longitudinal landing will probably cause disconnect, similar to that seen in the camera on Bacchus III.
There is no case, so it’s really easy for me to imagine bouncing the batteries out unless they’re retained somehow. Given that it costs us $2.50 for two of them, and we’re already spending $20 on the batteries, we could consider these consumables and just replace them every flight. The real challenge there is that we’re resoldering the most important solder junction in the system every flight, which is going to be bad for the PCB eventually.
Another alternative is to construct a little sleeve to go around the batteries, which could be as simple as cardstock (read: cereal box) and fiberglass tape (read: duct tape).
Jameco 216216: 6-AA, 2×3, no case, $0.75/unit
This a little 2 by 3 battery pack. In layout, it’s the same as the 216152, except that it’s only got three batteries in a row, and there are two of them back-to-back. It feels reasonably constructed, same as the last, but still not the totally solid feeling I’d like. The springs are less solid than the 216152, by a noticeable amount.
Most significantly, the middle battery in each row has the exact same “could get jostled out” problem as the middle two batteries had in the 216152.
We could resort to the same “consider it consumable” strategy here. This is cheaper than the previous solution, and I’m much more okay with burning $0.75 per battery load if it means we don’t have to worry about our power supply.
A sleeve is also an option here.
Jameco 2095453: 4-AA, 1×4, case, $0.99.unit
You know the battery cases Mitch uses for his kits? This is one of those, without the switch. It has the little hole for the switch, just no switch.
It’s 1×4, with a case around it. It snaps closed, and then is retained by a screw. It generally feels really solid, which is nice.
The one big concern I have here is the quality of the springs. They’re significantly weaker than the ones in the 216-series cases.
I’d go for the 2095453 vs the 216152. They’re both 4-AA, which is not ideal for our current payload, but they both feel really solid in their own ways. With a bit of testing, I’d feel confident that the 2065453 can handle the impact of landing, and then I’d be totally sold. Barring that, I’d prefer to make a dapper little sleeve for the 216152 and work with that a bit.