heavy ply sled?

[UPscaler]

Dad and I are building our first altimeter bay. It's the same inside diameter as PML 3 inch tubing. 3.002 I believe. Is it okay to use 1/4 ply wood to cut such a small sled? I can't imagine the weight difference being that big.

Also, what should we use to mount our PVC to the rings? Should we screw end caps into the bulkheads then glue the PVC tube into the cap? OR just glue the cap straight to the bulkhead?

 

[troj]

Dad and I are building our first altimeter bay. It's the same inside diameter as PML 3 inch tubing. 3.002 I believe. Is it okay to use 1/4 ply wood to cut such a small sled? I can't imagine the weight difference being that big.

1/4" plywood is just fine.

Also, what should we use to mount our PVC to the rings? Should we screw end caps into the bulkheads then glue the PVC tube into the cap? OR just glue the cap straight to the bulkhead?

Drill holes through the end of the caps and bolt them to the bulkhead. You'll have a hard time finding an adhesive that sticks both to PVC and to a bulkhead.

-Kevin

 

[dixontj93060]

Drill holes through the end of the caps and bolt them to the bulkhead. You'll have a hard time finding an adhesive that sticks both to PVC and to a bulkhead.

This will also allow you to maintain the cap if you have a problem, e.g., cracking--just unscrew and replace.

 

[Gnomad]

You'll have a hard time finding an adhesive that sticks both to PVC and to a bulkhead.

CA glue does an *amazing* job of bonding PVC to wood. Just be sure to scuff the contact surface of the PVC. If you need still more strength, build up a fillet using CA+baking soda.

 

[UPscaler]

CA glue does an *amazing* job of bonding PVC to wood. Just be sure to scuff the contact surface of the PVC. If you need still more strength, build up a fillet using CA+baking soda.

I think I will go with a small bolt to secure them. I found out how easy it is to remove CA when I needed to remove a motor block.

 

[karlbaum]

I have used 1/4" plywood in the past and it was okay. Now I use G10 because in a crash plywood can break and you don't want your sled to break damaging your electronics. You could fiberglass the plywood and it would be stronger.

 

[troj]

I have used 1/4" plywood in the past and it was okay. Now I use G10 because in a crash plywood can break and you don't want your sled to break damaging your electronics. You could fiberglass the plywood and it would be stronger.

Crash it hard enough, and G10 crumples, as well....

-Kevin

 

[sylvie369]

A crash that would break 1/4" plywood would very likely break several other parts (notably whatever is holding your battery in place). I've never been tempted to make my sleds from anything stronger.

I'd go with the bolt through the PVC cap as well, as that is going to take the brunt of the ejection charge force. You may find that you need to cut off the bolt inside the bulkhead with a cutting wheel (or a hacksaw) to keep it clear of the innards. I've gone to doing that rather than worrying about having exactly the right length of bolt.

 

[bandman444]

When I attached my ejection charge holders I always wanted a mechanical stop as well as a chemical bond that way if a bolt blows through then I have glue as a backup and if the glue comes un done them iv got the bolt in place....that just helps me sleep at night...you could see my avbay in my "Up in Flames" HPR thread. actually my canisters were aluminum tubing so I had to use a different method of "bolting" them to the bulkhead, but I will be using pvc in my next build.

What diameter are you using? How long? What do expect, or need it hold? Volume wise

 

[karlbaum]

A crash that would break 1/4" plywood would very likely break several other parts (notably whatever is holding your battery in place). I've never been tempted to make my sleds from anything stronger.

Unfortunately, I have been the victim of several crashes although I don't crash often I like to be prepared. My most recent crash was rather "successful" in keeping the av bay components in tact. I learned on my first crash years ago to install batteries forward of the electronics or on the bottom of the sled because they tend to break loose and damage whatever is in their way. I have had a crash where the 1/4" ply snapped and so did my altimeter But, that was before I used allthread to hold the bulkheads in place. All I am saying is that the black box should be strong enough so that it can survive crashes. But engineering will always have a balance between what is strong enough and what is too heavy. Yes G10 will snap but that is where the reinforced coupler tube helps.

Clear Skies,