Broken Rotor Axle

A project log for Goliath - A Gas Powered Quadcopter

A BIG Gas Powered Quadcopter

peter-mccloudPeter McCloud 02/17/2016 at 16:280 Comments

Test 41 was to determine if the starboard engine was working correctly again. After idling the engine for a while, the rear starboard rotor axle broke.

Looking at the slow motion video, it's clear that the axle breaks, and then the belt tension pulls the pulley inwards. This caused the rotor to hit support arms and sheared off a piece of the rotor. The double sided belt then falls off all the pulleys since the tension has been lost. Here are some pictures of the damage.

The rotor is the biggest issue, since a new one will have to be manufactured. The rotor pulley flange was dislocated as the belt came off, but it should be a simple fix to press it back on.

As hindsight is 20/20, it's fairly obvious that adding the grooves for the E-clips made it so the remaining material was insufficient to handle the loads. A 0.07" groove depth didn't seem like much, but the remaining material was only 0.485" in diameter, significantly less than the 0.625" shaft diameter.

The plan is to switch to 0.75" axles and bearings for the rotors. The new bearings are the same external size, so the pulleys won't have to be modified. The E-Clips will also be replaced with retaining rings. The rings won't be as easy to install or remove, but they only require a groove depth of 0.023", leaving 0.704" of material.

The new hardware has been ordered and the process of building the new rotor has been started. Meanwhile, the engine still appears to be running rough, so that will hopefully be addressed by the time all of the new hardware is ready in a couple of weeks.