Lipo in tight quarters

The Rocketry Forum

Help Support The Rocketry Forum:

ActingLikeAKid

Well-Known Member
Joined
Nov 17, 2015
Messages
1,133
Reaction score
13
Pinging the hive-mind....
I'm building a sled for my Eggfinder. As you can see, it fits perfectly... and there's even a little shoulder to snug it up inside the shoulder of the nose cone (the wider part of the sled fits inside a 29mm BT).
sled.jpg

The question I have is about the battery.The sled fits perfectly against the sides of the BT, which is nice and holds it in place, but there is just room for the battery between the sled and the inside wall. So unless I tape it on (which probably won't survive launch), I don't have enough room to secure it as-is. Here's the idea I had...

Cut a couple of small notches on each side of the side of the sled, and a "window" in the middle.
The battery slips into the window and is secured with zipties.
I'll probably glass the sled (at least this part of it) to strengthen it (it's just basswood)...
Would this work? Would I be better off epoxying the lipo directly to the sled and cutting it off if/when it dies?
 

ActingLikeAKid

Well-Known Member
Joined
Nov 17, 2015
Messages
1,133
Reaction score
13
An additional thought: Maybe I epoxy a little cylinder under the battery for it to push down onto - that 20g of battery gets pretty heavy under 10-12 Gs. (or, you know, 60Gs if I put that Loki motor in.....) :D
 

ksaves2

Lifetime Supporter
TRF Lifetime Supporter
Joined
Nov 25, 2009
Messages
6,261
Reaction score
489
Location
Central Illinois
Notch it like you mention and then epoxy in thrust blocks fore and aft on the sled to contain the battery so you can drop it in. Come to think of it, if the BT is a very tight fit, you wouldn't need the notches or the zipties just do the thrust blocks. Perhaps a little double stick while you plug it into the body tube.

I have a similar arrangement with an EggFinder TRS. I have zipties and thrust blocks but the sled is completely press fit. The nosecone shoulder base was removed so the duck antenna
juts up in the NC and the base abuts against the forward portion of the sled. Two terminals on the aft bulkhead for DD. It has a single separation and a cutter releases the main.

Kurt
 

MikeyDSlagle

Well-Known Member
Joined
Dec 17, 2013
Messages
2,540
Reaction score
508
I have something similar for my Adept22 in the NC of my Cowabunga. I drilled holes on each side of battery, rather than the notches and run zip ties through those around the battery. I think I have even less room with my setup. Thrust blocks are a good idea too. I'll try to get some pictures tomorrow.

Mikey D
 

OverTheTop

Well-Known Member
TRF Supporter
Joined
Jul 10, 2007
Messages
5,781
Reaction score
3,242
Location
Melbourne Australia
I use Velcro tape for all my LiPo mounting. The batteries are held onto the sled by the addition of cable ties (not pulled too tight). That way the Velcro takes the shear forces trying to slide the battery along the sled, and the cable ties prevent the Velcro from peeling. If your avionics bay is sufficiently skinny then force from the airframe might be sufficient to hold the battery to the sled, without the cable ties.

Here is a 500mAh battery for a telemetry system in a 54mm NC using the method discussed. Flown successfully to 62G acceleration.
Sled1resize.JPG
 

amarillo_rocket

Well-Known Member
Joined
Jan 20, 2009
Messages
292
Reaction score
0
Epoxy a small block of wood in the front and back. Add zip ties and you are good to go. I have mounted 9v in my ebays for years like this and never had a problem even on Mach 2+ flights.
 

cerving

Owner, Eggtimer Rocketry
TRF Sponsor
TRF Supporter
Joined
Feb 3, 2012
Messages
4,539
Reaction score
1,965
Cut a thin notch on the sled next to the battery and use 1" or 1 1/2" heat-shrink tubing. It adds very little bulk to the package. I would also recommend running a bead of RocketPoxy or equivalent around the GPS antenna, where it meets the metal shield. Don't use metal-bearing epoxy like JB Weld, though, it can detune the antenna.
 

ActingLikeAKid

Well-Known Member
Joined
Nov 17, 2015
Messages
1,133
Reaction score
13
Cut a thin notch on the sled next to the battery and use 1" or 1 1/2" heat-shrink tubing. It adds very little bulk to the package. I would also recommend running a bead of RocketPoxy or equivalent around the GPS antenna, where it meets the metal shield. Don't use metal-bearing epoxy like JB Weld, though, it can detune the antenna.
You mean at the base of it, where I kind of did a fillet of solder between the antenna and the PCB?
 

OverTheTop

Well-Known Member
TRF Supporter
Joined
Jul 10, 2007
Messages
5,781
Reaction score
3,242
Location
Melbourne Australia
I would also recommend running a bead of RocketPoxy or equivalent around the GPS antenna, where it meets the metal shield.
+1. Important for high-G flights, and even for surviving separation charge impulses an landing knocks.
 

SpaceManMat

Space Nut
Joined
Dec 20, 2013
Messages
694
Reaction score
64
You can also make some room in your av bay by changing the sled to a thinner piece of fibreglass.
 

Lowpuller

Well-Known Member
Joined
Nov 23, 2013
Messages
2,230
Reaction score
14
Second the zip ties suggestion, but would run them in both directions. You have plenty of room for zip ties.
 

ActingLikeAKid

Well-Known Member
Joined
Nov 17, 2015
Messages
1,133
Reaction score
13
I think I have a solution!!
Lowpuller, I *really* don't have much room for zipties:
FullSizeRender (16).jpg
because this is a 29mm tube with a 1/8" piece of basswood in it. There's very little room for anything. Which made me start thinking: It's not like I have a 2" wide sled in a 4" wide body... the sled is held in place at the top by the nose cone. If I cut the bottom perfectly square and do a nice Rocketpoxy fillet to hold it in place on the top , it can't go up (it pushes against the nose cone) it can't go down (it pushes against the transition), and it can't wiggle around (it's a snug fit inside the body tube). So rather than zip-tying the battery in place (again, it's not like it has much of anywhere to go except up or down), I make a little 'wall' of balsa around it. If the battery is at the bottom of the sled, it can't go down because it's sitting on the transition. It can't go up because there'll be a chunk of balsa in front of it. And it can't move side to side because there'll be a chunk of balsa next to it. Sort of ... a prison cell (blocks of balsa) instead of handcuffs (zipties). Unless there's something I'm missing, I think this should work (and I'll probably go ahead and glass the sled, just for a little extra strength).
sled.png
 

Attachments

ActingLikeAKid

Well-Known Member
Joined
Nov 17, 2015
Messages
1,133
Reaction score
13
Hmm, going round and round in my head on this:
Everything is a perfect snug fit with bare basswood.
But if I use double-sided tape to mount the Eggfinder, it might be too snug. And if I glass the basswood, it's DEFINITELY too thick.

Looks like I'm going to see if I can get a piece of 1/16 glass and make a fancy fiberglass sled. It'll be a bit heavier, but will be stronger and give me a tiny bit more room to work in there.
 

ActingLikeAKid

Well-Known Member
Joined
Nov 17, 2015
Messages
1,133
Reaction score
13
The problem is the clearance between the battery and the body tube... With no zip tie, the battery fits snugly between the sled and the body tube. If there were a zip tie around the battery, I think the body tube would snag on it as I slid the tube over the sled.
 

ksaves2

Lifetime Supporter
TRF Lifetime Supporter
Joined
Nov 25, 2009
Messages
6,261
Reaction score
489
Location
Central Illinois
The problem is the clearance between the battery and the body tube... With no zip tie, the battery fits snugly between the sled and the body tube. If there were a zip tie around the battery, I think the body tube would snag on it as I slid the tube over the sled.
If the fit is "that" tight, install thrust block fore and aft and press fit the whole shebang. If the battery can't flop around, you don't need the zip ties. I've done this on several
installations where the battery "just fits". If there is too much room and even a ziptie can't fit, make a thin metal strap and secure it with screws. Kurt
 

MikeyDSlagle

Well-Known Member
Joined
Dec 17, 2013
Messages
2,540
Reaction score
508
I agree with Kurt.
Originally I thought you were talking about 38mm, I see now it is 29mm. Looks like a nice snug fit. But a block on each side, that battery won't go anywhere.
 

OregonBAR

Rocketeer
TRF Lifetime Supporter
Joined
Jun 19, 2015
Messages
75
Reaction score
1
One other thing comes to mind, what about a smaller battery? I've found that the same capacity (mAh) will vary in dimensions from one brand to another... Or can you decrease your required capacity to something slightly less? Just looking at it from another angle...
 

cerving

Owner, Eggtimer Rocketry
TRF Sponsor
TRF Supporter
Joined
Feb 3, 2012
Messages
4,539
Reaction score
1,965
You mean at the base of it, where I kind of did a fillet of solder between the antenna and the PCB?
No, the square antenna on the GPS module itself. They are held onto the actual GPS module's PC board with one solder joint (the center pin) and a conductive double-sided tape, they're not soldered onto the shield. This is pretty standard practice for those kind of patch antennas, but they aren't resistant to high G loads (as in hard landings). Running a bead of epoxy around the base of the antenna where it contacts the shield will prevent the antenna from coming loose. In fact, I've seen a few landings where the GPS module actually sheared off the Eggfinder board leaving the antenna intact... at the very least, it's easily repairable with a new module, best case scenario you just clean up the solder and resolder the module back on.
 
Top