Brake Line for 38mm Tube (29mm mount)?

Wondering if anyone has ever run a brake line on a 38mm tube with a 29mm mount. There is very little space on the face of the centering ring (~1/8") to work with. The smallest brake lines I could find online were 3/16".

How have others been able to pass wiring through from your 2nd stage timer down to the motor with such limited space?

This is in regards to the Madcow Nike Apache for context.

I was doing a 54mm w/38mm MMT (RW Double Shot) instead of 38/29, but my local hardware store sells both brass rod and brass tubing (same place as the metal strips and all-thread), I bought the largest diameter tube that fit and used that.

woferry said:

I was doing a 54mm w/38mm MMT (RW Double Shot) instead of 38/29, but my local hardware store sells both brass rod and brass tubing (same place as the metal strips and all-thread), I bought the largest diameter tube that fit and used that.

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Ah, thanks! Lots of variation in size for brass tubing. That should work. Just need to take some wire and centering ring with me to store.


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Here's what I did for my 38 special:
2 strips of balsa glued to the motor mount. I made the notches inside the cr's with a chamfer so the starter pass easily.

Crumb fire said:

Here's what I did for my 38 special:
2 strips of balsa glued to the motor mount. I made the notches inside the cr's with a chamfer so the starter pass easily.

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Another great idea. I like how using the balsa will also help keep the weight down.


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Harbinole said:

Another great idea. I like how using the balsa will also help keep the weight down.


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Reminded me of how some folks do fin pockets with drinking straws, which is probably a workable approach here as well.

dhbarr said:

Reminded me of how some folks do fin pockets with drinking straws, which is probably a workable approach here as well.

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Ooo plus the flexibility will help in this tight of a space.


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I used a brake line in a Wildman Junior (38mm motor mount in a 54mm tube). It just barely fit, and I had to notch the coupler to make it fit.


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Another option for lightweight conduits is fiberglass or carbon tubing sold for kites. Usually available in a few diameters and lengths at a local kite shop or online.
-Ken

All the brake line I’ve seen is steel. For that reason alone I would recommend instead using something else. Carbon arrow shafts work well, as do paper soda straws.


Steve Shannon

Steve Shannon said:

All the brake line I’ve seen is steel. For that reason alone I would recommend instead using something else. Carbon arrow shafts work well, as do paper soda straws.


Steve Shannon

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I use the arrow shafts of some of my broken arrows as the tubes that I mount sleds on as a 1/4" rod fits inside perfectly.

You can get aluminum or brass tubes of various sizes at any good hobby store, brick or online.

I noticed aluminum tubes in the hardware section of Lowes too.

To the OP. Like in post 4, you may want to consider forgetting the tubing. As you mentioned in post 1, there is only 1/8" to work with. The thin wall 1/8 K&S aluminum tubing has a wall thickness of .014, which yields an ID of .097. All of the igniter wires I have, keeping the insulation on both wires, are .100 wide. You are looking at a tight fit.

I came up with a solution much like in post 4, and something like this makes for a smooth fit. I also slotted the rear of the motor mount to give additional clearance between the wire and the interstage coupler. It includes slots to move the coupler forward a little, a dam for when I epoxy the fins, and a strap for a motor retainer.

If you want to use a tube, look into the K&S thin wall 3/16. You would have to flatten it .050 and slot the CRs, but it would fit between the motor mount and inner wall.

It is a fun build...enjoy