Steering Take Off Dolly Design
8 Jul 01 - Photographs added
The dolly described here was created for my Delta 2000. It was essential that the dolly was steerable as the model has no rudder. I decided that I didn't want the expense of another RX, crystal and battery in the dolly. I also didn't want the weight of an additional servo in the model that would only be used on the take off run. Therefore the servo signals would have to be passed from the models RX via a detachable cable.
The following sketch details the main points of the design & the photographs show the end product.
To start with I moulded the 2 carriers using polyester resin and 3" wide glassfibre bandage. The rear moulding incorporated 'wings' that sit against the underside of the wing to stop the model rocking on the dolly. I then connected them together by glassing 3 wooden batons to them. 2 thrust pegs were made from long M4 bolts and some high density foam as cushioning. These were positioned such that the leading edge was touching them when located correctly in the mouldings.
To these I added the necessary cross bracing and the 1/4" plywood plates for attaching the undercarriage. The front undercarriage was attached using the 4 bolt holes in the pivot block. The rear undercarriage was attached using 4 small 'P' clips designed for cable - these grip the wire tightly to ensure no sideways movement of the undercarriage wire. I grabbed 3 wheels out of my stock bin - 2 1/2" rear and 2" front as that is what I had.
A standard servo was mounted to the lower frame. A pushrod was made by soldering 2 pieces of studding to a piece of brass tubing. The linkage was completed using ball joints at both ends to allow for any misalignment. Next was the bit that took the longest to work out.
I made up 2 special extensions leads. The first in the model had a standard socket to plug into the RX on both ends. One end was plugged into the RX and the other end was mounted flush in the bottom of the fuselage. The lead for the dolly had plugs on both ends. One end was plugged into the servo and taped up, the other left free. A piece of strong thread was attached to the free plug end and tied off on the lower longeron. The length of the thread was such that the connector would be plugged out of the model before an tension was placed on the cables.
The advantage of the extension cable on the servo lead is that if it gets damaged it is easy to replace.
Whilst this system was created for a specific model it can very easily be adapted to almost any model.
Model Plans & Designs