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Designing the Frame (February to March)

A project log for Goliath - A Gas Powered Quadcopter

A BIG Gas Powered Quadcopter

peter-mccloudPeter McCloud 06/01/2014 at 04:210 Comments

After picking the engine, some preliminary design work was done to estimate the total weight of Goliath and what type of structure might be required.  After using some conservative estimates for the various components and assuming a steel tube frame, the total weight of the quadcopter was estimated to be 240 lbs.  Heavy, but still within the capabilities of the motor.  An early CAD drawing of the quadcopter with the steel tube frame is shown below.

The layout was designed to not only support the components, but to also encompass the belt system.  This will protect the belts from external objects and help to keep a broken belt from flying outside of the frame.

However, after getting the engine and starting to lay out the structure, it was clear that adjustments were going to have to be made along the way.  A steel tube frame wouldn't be the easiest to modify, so a switch was made to slotted angle steel assembled using bolts,  both of which can be obtained at most any hardware store and allows the frame to be adjusted as needed.

The layout started with the center beams beneath the engine.  The weight of the engine required the larger 2 1/2" x 1 1/2" angle pieces versus the smaller 1 1/2" x 1 1/2" angles.  The center rails are slightly skewed from front to back, (see the following picture)  due to the locations of the engine mounting points.

With the top Center Beams in place, one of the Prop Supports was added.  However this configuration allowed the frame to flex significantly when loaded.

More supports were needed.  After trying different configurations, the layout below was used.  All of the pieces around the engine are 2 1/2" x 1 1/2" and the Prop Support is 1 1/2" x 1 1/2".  After applying some test loads, the flexing was found to be much less.

With the layout around the engine decided, a duplicate was built and placed underneath it to build a cage for the drive belts.  Some short pieces of 1 1/2" x 1 1/2" angle was used to connect to top deck to the lower deck.

Finally all of the Prop Supports were added and a piece of 2 1/2" x 1 1/2" was added to the end of each Prop Support to mount the prop shafts to.  At this point the frame the quadcopter is 7 feet long from corner to corner.  The stiffness of the frame is probably less than a steel tube frame would be, but the weight of the assembled frame is about 52 lbs,  about what was estimated for a steel tube frame.

More detailed list of measurements and instructions on assembling the frame will be added later.

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