Low Cost Adapters for Low Power Motors

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Scott Turnbull

This article describes some low cost, do it your self, options for putting smaller motors in upsized motor mounts.

One popular modification when building rockets is to upsize the motor mount. Upsizing the mount provides more options later for motor selection. Those upsized motor mounts provide the ability to scrape the clouds on large fields, but it’s also nice to be able to use the smaller, less expensive, motors on more modest fields. To use those smaller motors you need an adapter.

Shown here is a selection of burned motors to be used in making adapters. They are 18mm (A, B, and C6) , 24mm (C11, D and E), and 29mm motors.

When building a 24mm motor mount, you can choose to allow for the standard "D" length motors, or stretch the motor mount to allow for the longer "E" motors.

If a long mount is built, then one inexpensive adapter is a spacer that makes a "D12" motor fit into an "E9" mount. By comparing a D casing with an E casing, the appropriate spacer length can be marked and cut off of an expended 24mm casing. Peel a couple of layers of paper off of the spacer so that it slides in and out of the motor mount more easily. To use the adapter, just slide it up into the E length mount before installing the D length motor. A dental pick is a handy tool for later hooking onto the adapter for removal.

To use a 18mm motor in a 24mm mount, an adapter can be fashioned from a used 24mm motor. A 18mm casing fits snugly inside a 24mm casing.

Using a razor knife cut a slot in the outside of the 24mm casing. Cut a narrow slit all the way through the casing at the forward end of the slot to accommodate the forward hook of a motor retention clip. Cut the slot so that a standard motor clip fits flush into the slot. The 24mm casing, with its flush mounted clip, can be loaded with a 18mm motor and inserted into a standard 24mm mount. You can also use a section of 18mm casing as a thrust ring glued inside the 24mm casing. Make sure the forward end of the adapter has a hole for allowing ejection gasses to enter the airframe.

The same technique can be used to install a hook in an "E" length 24mm casing.

After upsizing to a 29mm motor mount, there may be a desire to use 24mm motors to fly on smaller fields. A previously flown single use 29mm motor casing can be used to create an adapter for loading 24mm motors.

Using a fine-toothed saw, slice off the 29mm motor nozzle. A thin walled 24mm motor mount will fit into the empty 29mm motor casing. The 24mm motor then fits into the 24mm motor mount. Make sure to enlarge the hole in the forward end of the casing to allow for ejection gasses to enter the airframe.

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

1. Motors
   Motor conversion! SO ...you got more time than money, and you like the A series motors? Here's one for you! The Estes A10-3T is ALMOST identical to the performance of the Estes A8-3. (according to their charts). Take a used Estes 18mm motor- A8-3 through C6-7. knock out the clay nozzle with a drill, knife, or screwdriver; BE CAREFUL! Take a 13mm motor, and cut off 1/4 or so, from the top. Test fit a 13mm motor into the 18mm motor. If it doesn't fit, take an x-acto, or similar knife, and strip a couple layers from the inside by slicing lengthwise down the inside, and removing a couple of layers of paper till the 13mm motor fits. Use aliphatic resin glue to hold all the insides down. Test fit a full size 13mm motor again into the engine casing to see if it fits well, and into thick end. Strip layers until the 13mm motor fits easily into the 18mm. Place some quick dry epoxy approx 1 1/4 inches in a ring up inside the 18mm motor. Take the 1/4 piece of 13mm motor you cut earlier, and insert it into the 18mm motor, followed by a full size spent 13mm motor into the 18mm casing, until the full size 13mm motor is flush with the end of the 18mm casing. Quickly remove the 13mm casing. (Just like placing any other engine block). When it dries, place tape around a 13mm motor, until it fictions fits insides the 18mm casing, and use as you would any other 18mm motor! VOILA! A regular A8-3 for the price of a mini motor. You can reuse the 18mm casing too! :) CHEAPER flights! – A.T. (FL)
2. Motors
   Remember, if you intend to use Aerotech composite motors as well as Estes black powder motors in your rocket, test the rocket for stability using the Aerotech motors. They are heavier than the Estes of the same size (18mm, 24mm). If the rocket is stable with the Aerotech motors, it will be more so on the Estes motors. An over- stable rocket is safer than a marginally stable rocket.
3. Motors
   You can make motor blocks from a section of used motor casing cut off with a razor saw and glued in position. - (D.S.)