RMS Delay Adjustment Tool

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By Art Applewhite

Brief:
AeroTech has published a procedure for modify the delay elements used in its RMS (Reloadable Motor System) motors. Delay elements may be adjusted for any length delay by following this procedure. This review describes how to build a delay adjustment tool from readily available parts so you can make this adjustment with precision and repeatability.

Construction:
Parts needed:

• 3/16 inch drill bit
• 3/16 inch to 3/16 inch Compression Union
• Metal rule marked in 1/32"

First a note on the selection of the drill bit. I choose the Vermont American Xtend brand of drill bit, part number 12739. This particular bit is made specifically for cordless drills. It features a unique speed geometry that combines an aggressive point that starts on contact with a fast helix that rapidly ejects material from the hole.

Construction of the tool is relatively straightforward. The 3/16" to 3/16" Union should be made from solid brass and have 5 separate parts: the main body, 2 sleeves, and 2 compression nuts. The center hole of the main body will need to be enlarged to 3/16" inside diameter. You can do that using the 3/16" drill bit that will later become part of the delay adjustment tool, an electric drill and a pair of vice grip pliers.

One of the sleeves will be modified to allow it to easily squeeze the drill bit and hold it firmly in place. I used a small triangular file to make 4 equally spaced notches in the end of the sleeve. The notches only need to be about 3/32" to 1/8" deep.

Assemble the tool by first sliding the drill bit into the main body of the union. Slide the unmodified sleeve over the cutting end of the drill bit. Slide the compression nut over the drill bit and sleeve and thread it onto the union. Tighten it finger tight only. The drill bit should still be able to slide in the union but there should be some resistance. Slide the modified sleeve over the back end of the drill bit and thread the other compression nut over it.

To set the tool, first calculate the required drilling depth from the AeroTech instructions. A general rule of thumb is 1/32" for each second of delay time reduction but always verify this with the instructions. Slide the union down the drill bit until only the need portion of the bit is sticking out. Use a 6" metal ruler with markings down to at least 1/32 of an inch to measure this distance. Tighten the compression nuts on the union with your fingers until the drill bit is held firmly in place.

When drilling the delay element, use your fingers only to drive the bit. Take your time and don't push too hard. The delay elements tend to be a little rubbery and pushing hard will cause the drill bit to go too far in and produce a delay time that is shorter than desired.

I have used this tool several times and it has proven to be very handy.

Also, you want to clean the tool after each use. The delay element material contains ammonium perchlorate and other chemicals that can corrode metals as will the sweat from your hands. To prevent corrosion, lightly oil the bit occasionally especially when storing it between launches and once a year disassemble the tool and clean all the parts.

Summary:
PRO: Durable, repeatable results.

CON: Not as cheap as the AeroTech suggested 12" of masking tape.

GUEST's OPINION:
"" (X.X.)