Eggfinder Apogee Mount Approach

[Zbench]

I started on a LOC T-LOC 4" rocket and thought it would be an ideal candidate to try out the Apogee Altimeter and mount kit that Cris recently came out with. I have a CNC prototyping mill, and decided to make up a two piece mount for use with the standard 4" LOC Nose Cone. I like the two piece version I made because it can allow access to inside the nose cone if I need to add weight or otherwise access the interior.

I cut off the end with a sharp knife and measured the resulting opening. Always tricky to get the perfect fit for an internal plywood mount, but after a few iterations I got the fit I was after. Shown here is the two piece mount right off the mill. Made out of 3/8" Baltic Birch Plywood



After cutting the parts out from the blank and smoothing the tabs that hold them in the sheet, I drove in 3 T nuts on the back side of the mounting ring and epoxied them in place for extra security. 1/4 X 20 is overkill for this size rocket, but I had the hardware on hand. Below is a view with the two parts assembled and the altimeter mounted. I had to file a slot in the mounting ring as I used thicker stock than needed plus there is a double thickness of plywood.



Once I was satisfied with the fit, I used Rocket Poxy to secure the mounting ring into the nose cone. Before I mounted the ring, I drilled a series of holes around the circumference of the nose cone that the rocket poxy could flow into and create a mechanical lock between ring and nose cone.



A few shots of the finished assembly. I added 3 #6 X 1/2" brass screws through the nose cone and into the plywood. Once seated, I draw filed the screw heads flush with the nose cone shoulder. I'm pretty pleased with the way the filed slot for the screw works. If you place a #2 phillips in the slot in the bottom it takes you right to the screw switch. Excited to finish this up and try it out. Rocket is complete, I just have to paint the rocket.

 

[Rocketless]

Don’t forget to drill a hole thru the two sets of rings so that pressure can be detected by the Eggtimer apogee
Would you sell the two plywood rings!
I would buy 4 sets if so

 

[Zbench]

I was thinking that I’d instead drill 3 small holes in the nose cone maybe 1/4” above where it meets the body tube. Any reason why this wouldn’t be a more direct approach?

 

[Rocketless]

I was thinking that I’d instead drill 3 small holes in the nose cone maybe 1/4” above where it meets the body tube. Any reason why this wouldn’t be a more direct approach?

I do not know if that would be more advantageous or if it would cause other issues, I am always worried about the law of unintended consequences, folks smarter than I am will chime in

 

[cerving]

Are you drilling a hole in the body tube so that it aligns with the hole in the NC shoulder? If you are, you don't need any more holes, the access hole will be fine.

 

[Zbench]

Cris, I wasn’t planning to, was going to keep it hidden. I guess I could though. Wasn’t planning to use shear pins with this so there is a chance the nose cone could rotate and still be a problem. Seems like the most direct route would be to vent the nose cone directly.

 

[Tractionengines]

Vent holes in the nose could over pressurize the nosecone. There are high pressure areas in the airflow where the nose is pushing the air out of the way. Vent holes on the body with a hole to equalize the nose to the body tube is a better idea.
YMMV

 

[jmuck78]

Don’t forget to drill a hole thru the two sets of rings so that pressure can be detected by the Eggtimer apogee
Would you sell the two plywood rings!
I would buy 4 sets if so

I second the request; I like the setup here.

 

[Zbench]

Just an update on this setup. I had a chance to fly it this past weekend and it worked great. I decided I would also like to put a TX transmitter inside the nose cone (another great reason to be able to change the contents) so I routed a slot and then put a mounting sled in there and braced it with some scrap. When the epoxy was dry, it was as solid as a rock. Wood always takes epoxy well. Here is a shot of me prepping it for flight on the tailgate of my truck. There is a 370 mAh lipo running the TX. I was getting 9 satellites that afternoon which is the most I have ever seen:



Headed up and away under the power of a H238T. I used the motor charge as a backup drilled to 10 seconds. It was perfect, sounded like it fired about 2 seconds after the altimeter charge went off. I had forgotten that the charge fires 1 second after nose over. That is a long one second, it was headed down and I was starting to wonder if I had the venting to the outside correct. I ended up drilling two 1/8" holes in the bulkead, and similar holes about 2 caliber lengths down the side of the main tube:



Shown here on the way down to the ground. I used a chute release and had it set for 400', worked perfect and didn't need the tracker at all. But, I had a solid signal on the LCD all the way down. Very pleased with how the Apogee Deployment Altimeter worked and the tracking hardware. The Apogee was beeping out the altitude when I picked it up, 1352 feet.

 

[Rocketless]

Just an update on this setup. I had a chance to fly it this past weekend and it worked great. I decided I would also like to put a TX transmitter inside the nose cone (another great reason to be able to change the contents) so I routed a slot and then put a mounting sled in there and braced it with some scrap. When the epoxy was dry, it was as solid as a rock. Wood always takes epoxy well. Here is a shot of me prepping it for flight on the tailgate of my truck. There is a 370 mAh lipo running the TX. I was getting 9 satellites that afternoon which is the most I have ever seen:

View attachment 479921

Headed up and away under the power of a H238T. I used the motor charge as a backup drilled to 10 seconds. It was perfect, sounded like it fired about 2 seconds after the altimeter charge went off. I had forgotten that the charge fires 1 second after nose over. That is a long one second, it was headed down and I was starting to wonder if I had the venting to the outside correct. I ended up drilling two 1/8" holes in the bulkead, and similar holes about 2 caliber lengths down the side of the main tube:

View attachment 479922

Shown here on the way down to the ground. I used a chute release and had it set for 400', worked perfect and didn't need the tracker at all. But, I had a solid signal on the LCD all the way down. Very pleased with how the Apogee Deployment Altimeter worked and the tracking hardware. The Apogee was beeping out the altitude when I picked it up, 1352 feet.

View attachment 479924

what is the precise transmitter and receiver you used for this set up?

Thanks!

i used this mount in a Mega der Red Max, but I used an ejection charge below the laundry inside a centrifuge tube, and a chute release at 400 ft, worked perfect

 

[Zbench]

I used Cris Erving's standard TX with upgraded 3dB antennae, and the LCD Receiver. You can read more about them here, If you can solder, I highly recommend these kits. They work fantastic and the technology you get for the money is a great value. Additionally, Cris is always adding features through firmware updates. It's a great ecosystem.

The nice thing about the altimeter in the nose is that there is no scenario where the charge doesn't get the laundry out of the tube. Of course, in these short stubby rockets. that is less of a concern, but I always worry about it.

 

[Zbench]

Bringing this thread back after almost a year. So I did vent the altimeter through the mount as shown above and then to the outside. I've flown this T-LOC 2-3 times and even though the holes are small, some BP residue is creeping into the nose cone area.

I completed a 4" LOC Goblin over the winter and we launched it this past weekend. I used a similar mounting system for an Apogee, but in this implantation, I drilled 3 evenly spaced 3/16" vent holes into the base of the nose cone itself. I also used a quantum so I could collect detailed data. In this method, the altimeter is vented directly to the outside air and there is no change for any BP gases to get to the electronics. I recognized that there was a risk, but I thought it low so went for it.

Happy to report that the Goblin flew great, reach a max altitude of 3042 feet on an I327DM motor. Below are two charts which show the altitude (raw and filtered) over elapsed time as well as the velocity (raw and filtered) over elapsed time. I was really surprised how smooth both curves were, especially the filtered velocity. Even the raw doesnt have as many artifacts as I have seen on other's data.

So, my conclusion is this is a very acceptable method for mounting an Altimeter in the nose of a rocket.