Final Prototype Testing, and Finishing up

We have done a several preliminary tests. We didn't have time to fine tune and completely define the relationship between force applied, RPM, and moment arm of counter weight. With our testing capabilities we were able to reach 1700 RPM while applying a 66 lb load on the circumference of the disc. This is a great success for us and a great proof of concept prototype. A video of a hand test, and one of the full tests is below.

In the next few weeks we are going to fabricate a new shaft (ours is off balance) and clean up the entire assembly to send to NASA before the end of the term.

Fabricated Test Fixture

After some heavy time in the machine shop, the fatigue tester was completed so that the we were able to begin testing. Below are pictures of the completed test fixture with the triaxially braided composite on the top. In the picture to the right, the polycarbonate frame that surrounded the fatigue tested can be seen. 

 Pictured below is a close up view of our force applicator which will be spinning around the composite material. Centrifugal force was utilized when applying the force. As the team reached higher revolutions per minute, the centrifugal force acting on the lock-nut became greater than the roller which caused it to apply the force.

Full assembly view

Roller/disc alignment

Initial assembly test

Strain gauge, proximity wiring on Arduino Uno

Full assembly

Up close of roller/disc interface. Bearing grease can be seen on roller face, indicating the high speed rotation during operation.

Gotta go to the shop...

We have been spending the bulk of our free time in the machine shop the past few weeks. Learning a lot, working on the assembly and hopefully having time to test.

Update

We have decided to revisit the centrifugal force application concept. It was ruled out months ago because its need for fine tuning, but at this point we needed a way to harness the centrifugal forces instead of fighting it.

We have been very busy redesigning, haven't had time for detailed posts. We have a good design now, we think we can get it together in time and we're feeling good about it now. We have about a month to build and test. It is going to be very busy. Here are some Creo models.

Central stationary shaft, with 2 bearings (red) in a bearing housing attached to a timing belt pulley. A steel channel is attached to the bearing housing and hangs out on both sides. The holes are a pivot point for the force applicator.

Force applicator operates when the centrifugal forces on the bottom mass (nut on thread) out weight the centrifugal forces on the roller (top). They pivot about the steel pin held by black collars.

This is the full functional assembly. The cylindrical bearing housing rotates the steel channel and pivoting force applicator around the stationary composite disc.

Big Design problem

We have been working on getting our design together to start ordering and fabrication in the past few days. Unfortunately, we have run into a problem in our concept that, embarrassingly enough, we overlooked while designing this concept.

The problem is overcoming the centrifugal force that will act on the roller as it spins around the composite disc. Because of the small radius and extremely fast rotation, even 5000 rpm, and 1lb weight estimation will cause approx 3000 lbf of centrifugal force. With our design that would require the spring to overcome that 3000 lbf to apply any force to the disc. I attached a quick sketch for clarity. 

We need to make drastic design changes, this will set us back enormously because we are suppose to be fabricating in a few weeks.

Winter Presentation Elevator Pitch

We made a video elevator pitch for our winter term presentation.

Quick Update Controls

In addition to solidifying detailed design, we are looking into the sensory equipment and controls we will need to implement. We will need a proximity sensor, strain gagues, signal amplifiers and a micro-controller at the very least. These are being spec'd out.