The original prototype is constructed from 25mm x 25mm x 2mm thick mild steel square tube for the main frame section and 20mm x 20mm x 1.25mm thick mild steel square tube for the cage arms. I believe the main frame section is over-engineered and consequently too heavy and so further models (including Sam's motor) will use 1.5mm thick tube for the main frame instead. The overall length for the main frame section requires 3000mm of steel. I've built the second frame with the new revision in order to get the total main frame requirement down to 3000mm so I can now get two main frames from one 6000mm length. The pdf file I've created of the dimensions for the chassis roughly follows the prototype with the use of 25mm x 25mm diameter square tubing for the main frame. Please note that the engine arms are off-center as the output shaft isn't central between the mounting bolt holes. If using 1.5mm thick steel instead of 2.0mm then I would advise 'inserts' or thick/large washers to spread the engine mount bolt pressure as I've already deformed the mounts on Sam's frame slightly when torquing down the engine. I recommend an APCO paramotor harness as the high hang points allow for a simple set up (no need for 'Roman Scale' type balance arms.

Click this image to download frame dimensions pdf.

This pdf is a revision (30th April 2009) as the motor mounts were found to be 25mm too high when building second prototype (Sam's motor). Sorry for any inconvenience.

To make the cage up I've used sections of 22mm round mild steel tube with an internal diameter of 15mm welded to the feet and cage arms. This allows the fitment of flexible pvc 15mm plumbing tubing to make the prop circle. The tubing is pop-rivetted to the arms and feet. Although a relatively flimsy material the tubing becomes fairly rigid once rivetted in. I'm not sure a heavy landing would save a prop while the engine is running but a dead-stick landing shouldn't cause such a problem.

These last three pictures show in order:

1) I've used some rubber washers to help reduce vibration. I'm not sure they really make any difference but they are there anyway.

2) While hang-testing the prototype I could feel the engine pulling down more on my right side due to the engine weight being offset. To compensate for this, the harness eye-bolt on the cylinder side is closer to the edge of the frame by about 1 inch (25mm) compared to the other side. This mod was also carried out on Sam's motor (see picture).

3) In the event of any torque effect trying to initiate a right-turn I fitted these anti-torque arms out of steel bar. They are roughly 8 inches (200mm) long and welded to be inline with the pilot's hips when fully seated in the harness. For extra comfort I have glued on a couple of foam grips which are the same ones used for the throttle handle.