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.

Spring Locking Mechanism Detail Design

We've worked on designing the locking spring force applicator and started a parts list and mapping out what materials we need to buy. detailed design is the first image and the second is the conceptual assembly.

Detailed design shows a large roller on an inclined linear slide. The roller slide assembly is pushed by the spring. This spring force will be adjusted by a screw in the back of the block.

This is a conceptual assembly. The detailed assembly design including motor, frame, bearings, and counter weight is next.

Piezo-electric concept will not work

We spent the last few weeks looking into what we need to build the piezo-electric concept. It turns out that our understanding of the actuators that we were hoping to use isn't near what we would need.

The actuators have a stopping force of 300lbs, but that is at 0.00" displacement.
The controller alone for what we are theorizing would cost up toward $30,000 and the actuators would be $2000 each. Way over our $3000 budget.

This means we will be falling back on our secondary design, the locking spring force applicator. This change late in the semester will set us back a bit.

Piezo-electric Design

We have decided to move forward with the piezo-electric design. We need to start detailed design of the piezo design to see if it will work with our budget. We have chosen the spring locking force applicator as our secondary design.

First Presentation

Our first presentation went well. We presented our concepts and discussed moving forward by choosing a concept and starting detailed design.

Rotating force

Linear actuator design

Piezo-electric Design seems to be ideal at this point.

Concept Sketch Spring Lock

We are considering how we plan to apply the rotating load. We think the most adjustable and clean way is to use a spring locking force applicator. This will eliminate messy wiring and complicated linkages.

This sketch shows the basic assembly and function. The spring compression can be adjusted with a screw, pushing more or less on the plunger with roller attached.

This sketch shows how the spring roller assembly would fit on the overall rotating assembly.

Centrifugal Concept Sketch Video

Here's another video sketch explaining one of our concepts in more detail.

Rough Concept Sketches

We have generated several concepts that have a lot of potential. They're shown here in rough sketches.

Piezoelectric actuators will be mounted around the composite disc. These actuators will fire off in sequence in a rotational motion. This will simulate a rotating load without the need for actual rotation.

This method involves using a linear actuator and a series of linkages to transfer a vertical force to a horizontal force that acts on the circumference of the disk. This allows the electrical wires needed to operate the actuator to remain fixed while the linkages spin.

This horizontal design was inspired by the orientation of a lathe to keep the system stable at high speeds.

This concept utilizes the centrifugal forces that are in effect at high rotational speeds. This concept uses a purposeful unbalance to apply a load to the disc. The limitation is that it is difficult to control the load magnitude because it has 3 variables that effect it. It will need to be very fine tuned. 

Communications Problem Definition

The problem has been defined. We are working remotely with Dr. Kohlman so ease of communication isn't ideal. So I have made a video that details out the problem definition to be sure we are on the same page.

This proved to be a very effective communication tool.

Project CRoFT Overview

Hello

We are a Senior Design team from Drexel University that is working with NASA Glenn Research Center. We are tasked to design a Composite Rotary Fatigue Tester (CRoFT). The team members are Timothy Chua, Dylan Paproski, Joseph Rappazzo, and Nikhil Tandon. Under the supervision of Dr. Leslie Lamberson and guidance of our NASA contact, Dr. Lee Kohlman, we will design and build a prototype rotary composite fatigue tester.

Composite materials are often utilized to reduce the weight in structural components. In this case, the composite material serves as the web of a gear between the metal hub and the teeth of the gear. In drive train applications of these gears, there are radial vectors and overturning moments applied to them which cause fatigue. Our goal is to prototype a testing machine that will simulate these rotating loads.

The specifications of this project are to design a test fixture that will have the composite gear undergo a radial load vector with an amplitude of 300 pounds while operating the test machine at a rate of 5000 rotations per minute. The second goal of this project is to have 5x the rpm of the original speed in order to achieve accelerated fatigue testing. While the disc is undergoing these conditions, the deformation of the disc is to be measured. The last goal that is trying to be accomplished is to generate a rotating overturning moment on the composite disc without rotating the test article. 

This description is the current overview of the project and with the help of our adviser and NASA contact, we are looking to design an effective test fixture that will satisfy all these goals, and help with the development of hybrid composite gears.

-Team CRoFT