29mm Min-Diameter High Performance Scratch Build Thread

[Adrian A]

Catching up on my build updates, this will be about the av-bay, which I'm mostly done with. No launch for me tomorrow, partly because of a poor weather forecast, but mostly because I'm not done yet.

Here is the bottom of the chute cannon. I'm using a .1" header for the Raven electrical connections. I made a little bulkhead that fits inside the coupler, using the the new belt sander, and marked it with some ink on the header while everything was put together inside the coupler:



Here are some more views of the H-beam tray I made with some more 15-mil fiberglass:




The nuts are just epoxied onto the sled. I was thinking that I would need to put a layer of fiberglass over them to help hold them down, but then I found out how solidly they are attached. I sanded the nuts before installing

When I was test-fitted it together, I noticed something, see if you can spot the problem:


The Raven on the bottom needs to be able to slide backwards to get off of the header pins, but I didn't leave enough clearance behind the screw terminals. So, I started over on the H-tray since the nuts were glued on more strongly than the rest of the tray. This time I made another foamcore jig to hold the H together during curing.

Here's more detail on the cannon side of the bulkhead. I could tell that I wouldn't have room for axially oriented terminals like on a regular Featherweight av-bay, so I'm installing them radially. These are just brass nuts soldered to the header with short pieces of wire.



The white tube with the holes is how the parachute harness will be attached later.

Not that you can tell in the picture above, but I filled it in with epoxy and low-density filler so that the wiring and nuts are all potted into place. To prevent the threads from getting clogged, I put some grease on the screws and installed them during curing.
Here's how I decided what length to cut the chute cannon. I installed the parachute, piston, and left some space for the charge, and marked that depth with blue tape. I arranged each of the pieces to see how much I would be able to cut down the nosecone and/or airframe. It turns out, no length reduction looks likely at the moment:




Next I glued the bulkhead onto the new H tray, and got ready to do the critical alignment of the chute cannon so that it is perfectly centered inside the cone. I put an 18mm-29mm transition ring on the end of the cannon, and assembled everything inside the cone and the coupler, with the cannon moved forward until it couldn't go any farther.

The result is shown below, which also shows the wire whip antenna placement (in lieu of the SMA connector antenna) and replacing the battery terminal block with a battery connector:

 

[Nytrunner]

Really fine work there. I'm a long way from trying anything complex in that size.

Was that a launch lug for your harness tube? The spiral looked familiar

 

[Adrian A]

Yes, that's a launch lug. Here is after I added the tracker batteries. There are some 150 mAhr batteries that conveniently are the same width (0.79") as the boards, so I soldered 2 in parallel to provide 300 mAhrs for the tracker.

 

[Adrian A]

I made some progress on the av-bay tonight.

I glued on the rear bulkhead. It's a Featherweight 29mm active bulkhead which I'm just using for its magnetic switch. I started with 5 minute epoxy and it failed almost immediately, so i cleaned it up and glued it back on with the good stuff with some colloidal silica mixed in, and so far, so good. I do plan to do some reinforcement before flight.

Next I soldered on a new battery JST-PH connector for the battery, since I had to relocate it anyway. Photo is through a microscope I use for almost all of my soldering.


It's not obvious from the photo, bu the white battery connector is flat on the bottom of the tray.

Here it is with a Raven4 prototype and 150 mAhr installed. The battery is a 150 mAhr single lithium ion cell, modified to shorten the connector wires and solder them directly to the unprotected pads on the circuit protection board so that the deployment current won't get interrupted.



I ran a test flight with some 1 Ohm and 5 Ohm load resistors installed and made sure that they were firing with decent current from that little battery. All went well.

Flipping it over, here is the tracker side:


When it's all installed in the airframe:



I'm planning to use some epoxy to laminate some kevlar braided cord from the chute cannon, back around the back of the back bulkhead and back to the front again to make sure everything stays together if I get a bit jerk when the nosecone is ejected. I'll also probably put a little fiberglass reinforcement connecting both bulkheads to the h-tray. Then drill the chute cannon wire hole, glue in the coupler, pot a small split ring into the front of the nosecone, work on my piston and apogee charge holder, and then I'll be ready for deployment charge testing. There could still be enough time for me to get this done before a launch in Pueblo on Saturday

 

[OverTheTop]

Looking good Adrian . It is seriously going to go off like a gunshot! What's the peak accel?

 

[Adrian A]

Yesterday I flew this rocket on a G80 at the Southern Colorado Rocketeers (SCORE) Christmas launch. It was a successful fligh tand matched the sims pretty well, reaching an altitude of 5128' (GPS) and 4991 (barometric).

Here's a zoom in of the boost and initial part of the coast, recorded with a new Raven4 altimeter:



Peak acceleration under thrust was 32.7 Gs, and the max drag at Mach 0.8 was -5.8 Gs. The fight seemed very very straight, and the accel data bears that out. There is no real sign of any lateral acceleration after it departed the tower.

Here's are the details near apogee:


I was wondering what caused the divot in the baro plot. Finally I realized that it was the motor delay charge burning through. I had removed the deployment charge but not plugged the hole into the motor, so when it got to the time when it would have deployed, there was some smoke charge output feeding into the av-bay. The apogee deployment was really pretty benign at -14 Gs to kick off the nosecone and then about 6 Gs when the shock cord went tight.

Here is an overall view, including the temperature and the deployments this time. Interesting how the temperature showed slight variations (magnified here) that might be related to the orientation during drogueless descent. Once it was under chute then the temperature started climbing, probably partly from the heat of the chute cannon going off nearby.


The descent rate was -50 to -80 feet/second before parachute deployment and around 20 feet/second after. The rocket landed about a half mile away, totally undamaged. The Featherweight GPS tracker took me right to it.

 

[AeroAggie]

Nice work Adrian! Your avbays are inspiring me to try harder to shrink my designs a bit.