Hints & Tips
DIY - Bungee Launcher Dolly
By Carl Tulanko
September 08, 2007 - 07:15:54 AM

	A 3/16" piece of steel rod from the hobby shop is used for an axle. It is marked for cutting at 13 1/2" in length	The rod is shown being cut and the ends are then flattened
The rod is cleaned with very fine sandpaper, followed by alcohol	Most wheels have 5/32" axle holes, so I used a spare pair of 2 3/4" lightweight wheels and drilled them to 3/16" diameter to fit the axle	You may have to sand/file the hole so it spins smoothly and without play on the shaft rod you made
Loktite is used to install the set screws in six 3/16" wheel collars that are used	Set screw shown installed in wheel collar	Clean up the excess Loktite with a Q-Tip
The first Wheel is installed and the Wheel Collar is tightened flush to the shaft	A second wheel collar is installed to hold the wheel in position. Make sure the inside wheel collar is not binding so the wheel can spin freely	1/16" braided steel cable is purchased from Home Depot, Lowes or any other similar store. You will need about three feet of cable
Aluminum Ferrels are also purchased for the wire. You will need three of them and they come two to a pack	The first ferrell is placed over the wire end	The wire is looped around and inserted into the other side of the ferrel
The wire is pulled tight so that the loop can just fit over the 3/16" axle shaft	Once crimped, you can solder the wire together for additional safety	Wire shown crimped and soldered

I used the side of a steel ruler to flatten the center of the ferrel and crimp it as shown	Photo shows a closeup of the crimp	A second ferrel is slid over the wire, then loosely looped back
A third ferrel is slipped over the other end of the cable and the wire is passed through to make a large loop	The center ferrel is shown in the photo on the left with the space between the two ferrels measured as seen	The center Ferrell is also adjusted so a 1" loop extends past it as shown below
Masking tape is used to hold the center loop and wires in position. Do not crip the center yet	The third end ferrel is adjusted over the wire to the same space of 12" between it and the center ferrel	The end is adjusted to fit over the 3/16" shaft, then it is crimped in place

The other end ferrel shown crimped and the wires have been soldered

Both ends shown even to eachother with similar sized loops

Tape is removed from the center ferrel and it is slid up the wire to form a 1" long loop

keep the two end loops together so the center loop is not made lobsided, then crimp the center ferrel as shown	Wire completed with two ends and a center loop	One of the loops is slid over the shaft
The wire loop is tightly retained with another Wheel Collar	Two pieces of 3/16" inside diameter brass tube are cut to about 1/2" in length	The tube is slid over the shaft
Both brass tubes are installed on the shaft	Slide another wheel collar on the shaft	The other wire end is installed on the shaft

Another wheel collar is loosely installed as shown

The second wheel is installed on the shaft

The final wheel collar is installed and tightened flush to the shaft end

The inside wheel collar is tightened against the wheel, but make sure it can spin freely. Finally, tighten the inside wheel collar tight against the wire loop

Once the inside wheel collars are tightened, remove the one outside collar and wheel

The right wheel was removed so you could more easily measure the distance between the two inside wheel collars. The distance is shown below as 10 1/2"

Make a center line using a marker at half the distance between the two collars, in this case 5 1/4"

Push the brass tube up against your mark, tape it in place so it doesn't move around and draw a full circle around the center line

With both brass tubes pushed to the right of center, epoxy is applied to the shaft on the left side of the center mark

The brass tube is slid past center and over the epoxy, then the excess epoxy is cleaned. Glue is applied to the right and the right side tube is slid over the glue back and forth until it fills inside, then the excess epoxy is removed from the right side tube

Position the two brass tubes evenly on each side of the center line with about a 3/16" thick space between them as shown. Let the epoxy set up

Bungee Dolly shown completed and ready to use

The towhook of the aircraft is hooked at the center of the Dolly axle, between the two brass tubes. The front loop of the Dolly is attached to the bungee cord using a 1/8" Quick Link