Madcow Tomach Build Thread - "Not an Engineer"

The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

AlnessW

Well-Known Member
Joined
Oct 6, 2013
Messages
1,221
Reaction score
3
Merry Christmas everybody!

Guess what Santa Claus got me this year... :D
IMG_2867.jpg

Background
I had been toying around with the idea of building one of these for several months now, but then opted to wait until after Christmas to order one! I've seen lots of these fly before and it just looks like a neat high-performance rocket. This will sort of go hand-in-hand with my 75mm MD rebuild and venture into research motors.

IMG_2870.jpg
Kit contents, including av-bay components, fin alignment guides, and one continuous shockcord.

IMG_2871.jpg
36" booster section next to an old K250W case for comparison. Oohoo!

Design
The kit did include an instruction sheet but of course I'll hardly reference that! ;) As usual there will be a certain amount of kit-bashing involved. I debated the idea of a zipperless design but will more than likely go with the traditional dual deploy configuration. I'm going to want to push this thing pretty hard, so I'll obviously do tip-to-tip on the fins and all that good stuff.

In a nutshell, here is what I have in mind:

  • Adhesives - Why, "that boat glue" of course! :wink: Seriously though, I'm thinking about something like Aeropoxy, Cotronics or ??
  • Altimeters - Most likely a Raven2 backed up by a Stratologger.
  • Chutes - Drogueless on top, followed by either a 36" or 45" main.
  • Motor retention - Slimline.
  • Shockcord attachment - Still TBD, but most likely just an eyebolt on the forward closure.
  • Tracking: BRB900 (in the nosecone) like always.
I washed all the fiberglass parts today, but av-bay construction will hopefully begin tomorrow!
 
Last edited:
Oh no you didn't.

To Mach or To Mock?

I hope yours is the former and not the later.
 
Oh no you didn't.

To Mach or To Mock?

I hope yours is the former and not the later.
Somehow I knew you'd be the first to comment! :) Fingers crossed for the former indeed...

You gonna tower launch this thing or add buttons? Does the Slimline cause any trouble in a tower?
I had planned on using buttons but I've never launched from a tower before. I can't imagine why a Slimline would be a problem though.
 
I am currently building the 54mm CF Tomach so I will be interested in seeing what choices you make. Mine is pretty much assembled just doing the electronics and a finishing. I have not installed rail buttons or a retainer yet, as I am still undecided on the launch tower vs. rail and slimline vs. Aeropack internal MD retainer.
 
I got the FG one for Xmas. Will be going with the Aeropack MD internal retainer. I plan to build in threaded inserts that will allow me to remove the buttons if I so desire. Electronics will be a Marsa54L. I actually plan to use the motor ejection charge (if available) for the apogee event with a 120" TF Ultra Streamer. Main will be a 30" CATO-Chute. Will use the Wildman icky black goop for assembly (technical term as I seem to get it everywhere during builds).
 
If you decide to go aeropoxy, I have loads of both the ES6209 (adhesive) and PR 2032 with PH3630 (laminating epoxy resin and hardener) and i also have a crap load of both carbon fiber and fiberglass. Actually I have everything you need to build a badass to-mach :)
 
I got the FG one for Xmas. Will be going with the Aeropack MD internal retainer. I plan to build in threaded inserts that will allow me to remove the buttons if I so desire. Electronics will be a Marsa54L. I actually plan to use the motor ejection charge (if available) for the apogee event with a 120" TF Ultra Streamer. Main will be a 30" CATO-Chute. Will use the Wildman icky black goop for assembly (technical term as I seem to get it everywhere during builds).

Interesting idea on the threaded inserts but where are you going to insert them? I used some for attaching the altimiter bay to payload bay however they are not flush.

View attachment 249880

I haven't done a final weigh in for the chute size but I was going to use a 15" drogue, however I like the idea of a highly reflective streamer

I am still on the fence using my Aeropack MD retainer mainly because you have to decide where you want to place it based on the motor. Otherwise you have to mess around with an extension or multiple extensions. Alternatively it was suggested to me that I could drill multiple mounting points for the retainer, which I would tap.

My altimeter bay is a dual design.

View attachment 249878

View attachment 249879

If you decide to go aeropoxy, I have loads of both the ES6209 (adhesive) and PR 2032 with PH3630 (laminating epoxy resin and hardener) and i also have a crap load of both carbon fiber and fiberglass. Actually I have everything you need to build a badass to-mach :)

I used AeroPoxy ES6209 for the fin root and any assembly, ProLine 4500 for the fillets, and just waiting for my new jig to do a 3K 2x2 Twill T2T layup using AeroPoxy PR2032 with PH3660
 
Last edited:
I was just on TopFlight's site and I could only find a 100" Ultra, are you having them make a custom 120", and do you know where I can get one with a reflective material?

I have had Gary make me a custom streamer and he had gold reflective material. Email him.
 
I have two 120" ones - they are a bit old, so they may not list them. As Tim noted, Gary is really accommodating with respect to semi custom work.
 
I am currently building the 54mm CF Tomach so I will be interested in seeing what choices you make. Mine is pretty much assembled just doing the electronics and a finishing. I have not installed rail buttons or a retainer yet, as I am still undecided on the launch tower vs. rail and slimline vs. Aeropack internal MD retainer.
Very cool! I am undecided as well, but will touch on some pros and cons below.

I got the FG one for Xmas. Will be going with the Aeropack MD internal retainer. I plan to build in threaded inserts that will allow me to remove the buttons if I so desire. Electronics will be a Marsa54L. I actually plan to use the motor ejection charge (if available) for the apogee event with a 120" TF Ultra Streamer. Main will be a 30" CATO-Chute. Will use the Wildman icky black goop for assembly (technical term as I seem to get it everywhere during builds).
The main issue I see with the Aeropack MD retainer is having to determine where to put it in the airframe with regards to motor length. Granted, I'll probably be mostly flying longer 54mm motors in this rocket (e.g, 54/2560 and up) but it would be nice to have flexibility and not have to worry about extensions, etc...
If I want to get fancy, I may add a streamer as a drogue but will probably just leave it as a tubular nylon strap. As for a Marsa54L, I think that's a 4-channel but will still fit in a 54mm coupler? "Icky black goop?"

If you decide to go aeropoxy, I have loads of both the ES6209 (adhesive) and PR 2032 with PH3630 (laminating epoxy resin and hardener) and i also have a crap load of both carbon fiber and fiberglass. Actually I have everything you need to build a badass to-mach :)
Sweet, thanks!! I think I'll definitely take you up on the "badass Tomach" offer. ;)

Interesting idea on the threaded inserts but where are you going to insert them?
Good question. Where would you put them?

My altimeter bay is a dual design.
I will be using a similar design with 2 charge caps on each side of the av-bay. What are those little machine screws poking out for?
 
IMG_2873.jpg
Drilled-out bulkplates and most of what's included with the av-bay kit. (I had to add a few nuts/washers.) I also noticed that the kit came with 3/16" all-threads instead of 1/4" like I usually use. Just as well since it would appear as though 1/4" wouldn't have fit, anyways.

IMG_2875.jpg
Assembled components. I also like to use wingnuts for the top lid, but those wouldn't really fit either...

IMG_2874.jpg
Tada!
 
I hate to burst you bubble but, I highly suggest you swap those eye bolts for some either welded or forged.
I've seen a few open up.
Probably won't happen unless a high speed deployment occurs.


JD
 
The main issue I see with the Aeropack MD retainer is having to determine where to put it in the airframe with regards to motor length. Granted, I'll probably be mostly flying longer 54mm motors in this rocket (e.g, 54/2560 and up) but it would be nice to have flexibility and not have to worry about extensions, etc...

I use the extensions as noted. Works for me.

If I want to get fancy, I may add a streamer as a drogue but will probably just leave it as a tubular nylon strap. As for a Marsa54L, I think that's a 4-channel but will still fit in a 54mm coupler?

My lousy eyes do better at apogee with the streamer. Visual aid and all that.

"Icky black goop?"

The black Proline epoxy. Whenever I use it, I get that stuff everywhere, can't explain it, I just do.
 
Last edited:
I hate to burst you bubble but, I highly suggest you swap those eye bolts for some either welded or forged.
I've seen a few open up.
Probably won't happen unless a high speed deployment occurs.
Understood - and I do normally use forged eyebolts, however this rocket isn't particularly heavy so as of this moment I'm not too concerned.

My lousy do better at apogee with the streamer. Visual aid and all that.

The black Proline epoxy. Whenever I use it, I get that stuff everywhere, can't explain it, I just do.
Visuals are always good, but if I'm trying to push this thing 15K or higher then I don't think I'm going to see much of anything with our without a streamer...
 
Visuals are always good, but if I'm trying to push this thing 15K or higher then I don't think I'm going to see much of anything with our without a streamer...

You can see a streamer or shiny fins flash at 15k on a clear sunny day. I have followed several flights from that high all the way down.
 
What are those little machine screws poking out for?

Those are 316 stainless 4-40 socket cap screws inserted into a mini rail button spacer and washers, for insulation and secured by one 316 nut and washer on the outside face of the bulked. The inside has a ring terminal secured to the socket cap head sandwiched between two washers and crimped then soldered to 20 gauge stranded hookup wire. I stripped off the ring terminal insulation as I added my own colour matched heat shrink tubing. The hookup wire had to be special ordered as I wanted the have 8 unique colours, one for each post, plus black and red for power. The wire was sourced from ActiveTech.

820X100A - White
820X100B - Black
820X100C - Red
820X100D - Green
820X100E - Yellow
820X100F - Blue
820X100G - Brown
820X100H - Orange
820X100I - Grey
820X100J - Violet

The mini rial buttons spacer and washers were just a fluke in that I ordered a bunch of them them for my BadAzzz mini missiles and just tried them as a solution to providing insulation from the carbon fiber. The O/D also fit the drill bit I had for my dremel perfectly and the I/D is a snug perfect fit for the 4-40 screw, when I say fit it is literally a press-fit. My tests showed that this material was non-conductive, using a fairly sensitive bench top multi-meter.

I still have to field test to ensure the non-conductive properties of the insulator plus to measure the resistance that the screws/washers (TB) adds to ensure that it is low enough not to interfere with the e-match. I have already had a deployment failure due to the latter. This is why I purchased the multi-meter, to measure resistance below 1 or 2 ohms, which your typical handheld cheapy multi-meter is not capable of.

On each outside post I will wrap an the e-match end around on the post and sandwich it in-between two washers, then secure it with a two nuts.

So to answer your question the machines screws are the terminal posts for the e-matches :wink:
 
Last edited:
Head on over to the URRG forum (much more open than here) to see my "minimum diameter" built thread. The quotation marks are because of the ACME fincan. Maybe there will be some items that provide you some insight!

https://forum.urrg.org/index.php?topic=68.0
Cool - thanks Dan!

On each outside post I will wrap an the e-match end around on the post and sandwich it in-between two washers, then secure it with a two nuts.

So to answer your question the machines screws are the terminal posts for the e-matches :wink:
"All a long-winded way of saying..." :)
But seriously though, that's a good idea. I am still debating how I'll wire my ematches in place, since I don't have room for terminal blocks. It's also quite possible I'll go "old school style" and just wire them more-or-less directly into the altimeters.
 
I was browsing around on Perfectflite's website a week or 2 ago when I came across their new StratologgerCF altimeter!! :) This rocket was just the excuse I needed to order one:

IMG_2888.jpg
Note the size comparison...

IMG_2891.jpg
And here she is!

IMG_2893.jpg
Next to the Raven2 of which I'll be using as the primary. Not really that much bigger!

IMG_2894.jpg
Altimeter sled in place.

IMG_2899.jpg
And both altimeters mounted!
 
I really, really wanted to use Featherweight magnetic switches in this rocket, but I just couldn't get myself to spend the money on them. After some shopping around, the next best option seemed to be Missileworks screw switches. They are substantially larger than Featherweight screw switches (like the ones I'm using in my 75mm MD) but work the exact same way and are a bit cheaper.

IMG_2911.jpg

IMG_2919.jpg
Wiring and switches installed, sans solder. It was a tight fit, but I managed to cram everything in there. (9V batteries on the back.)

Also! Mike Fisher will be machining me something very cool for this rocket...
 
IMG_2920.jpg
Av-bay secured in place via machine screws.

IMG_2921.jpg
For this build, I decided to finally attach the av-bay "correctly" to the airframe. Normally I just use sheet metal screws and tap into the fiberglass, but this time I used hex nuts inside the coupler.

IMG_2924.jpg
Here's what they look like - just standard hex nuts with a dollop of epoxy.

IMG_2927.jpg
Yes, I know I should have used t-nuts, but they just wouldn't fit.

IMG_2928.jpg
Holes drilled for shear pins and screw switches.

IMG_2931.jpg
And here we have the av-bay in place, complete with screws, shear pins, and switch access points.

IMG_2932.jpg
For the fins, I bought some various building supplies off my friend Jeremy (aka junkyard). For adhesives, I'll use Aeropoxy ES6209 and PR2032/PH3630.

IMG_2934.jpg
And now for the composites! Kevlar and a few yards of fiberglass cloth. :)
 
Back
Top