Arm Segment Fabrication

Arm Segment Fabrication

Date: 3.25, 3.28, 3.29
Goal: Fabricate sections of the arm and test the new gas spring.
Time: 6 hours
Students: Taren and Grant
Instructors: Mr. Pitz and Mr. Johnston

This segment of the project was much anticipated as the results of the test would direct us as to what we would have to fabricate in the future.  After some extensive testing (see past blog posts) we ordered a couple of gas springs (30 and 40 pound tension) to test on the arm to see if they could replace a traditional spring. We wanted to go with the adjustable gas springs, but they were cost prohibitive. Also, if we let too much gas out, we would have to send the spring back to be recharged. We did feel however the adjustable gas spring would be the best choice for the application.

A trip was made to PT Welding and Driveshaft in La Crescent to see if Pete had any 1 1/2" aluminum tube stock. He had a some shorts he gave us for free that worked out well for our horizontal arms. Thanks Pete!

The first thing we did was make the aluminum sides by cutting and then using the vertical mill to remove the metal where the spring would be placed. You can see a video of the action below.

Tube stock placed in milling machine

Milling out opening for shock and support arm.

Next the horizontal arms were cut and drilled to accept a 1/4" bolt to make a pivot point in the corners. We attempted to use plastic washers wherever metal met metal. The aluminum still needs to be filed and polished up. Research was done on the shear strength of a 1/4 in zinc plated bolt. We felt the rating was close to what we needed, but are considering replacing the bolts with a new graded bolt.

We will now need to make one more of these except with a 40 pound spring because it will connect to the one you see below and need to support more of the mass and load.

Horizontal arms drilled and bolted in place with gas spring attached.

Bolt head and plastic washer. 

Mr. Pitz started working on a design for the grinder mount. Part of this was previously completed but we were still looking at different ways to mount it to the arm and allow for flexibility of movement. We picked up some flange bearings (5/8") that we thought might make the rotation easier and smoother, then turned down some aluminum blocks on the lathe to accept the bearing. This will allow the grinder to rotate up and down while in the mount.

End blocks with bearings inserted to help grinder rotate smoothly.

We now have the mount to the point where the grinder will move up and down and rotate around its center longitudinal  axis. The next part will be to secure the grinder mount to the arm so it can also rotate right and left perpendicular to the body.

Linear Block Fabrication and Electrical Considerations

Linear Block Fabrication and Electrical Considerations

Date: 3.21.17
Location: Logan HS
Goal: 1) Fabricate linear block to move on linear rail system. 2) Design an LED indicator warning system for our electronics that drive our linear actuator.
Students: Taren and Grant
Time: 2 hours

Taren and Mr. Pitz worked on taking the two linear blocks that ride on the rail system and mounting them on a block of alum. to increase the strength and rigidity of the system. This is important because the arm will mount to this block system and it will have to support the load of the entire structure.

Dave Foye came in to work with Grant on a LED Indicator warning system. Basically this will be mounted on our circuit board to let us know if we have power to certain areas of the actuator or H-Bridge. It makes it easier to troubleshoot if you can visually see if an LED is on to indicate you have power to that specific area.

Sketch of ideas for using an LED warning indicator array.

Linear Block

Linear Block-View from front side with machine bolts mounting the alum. to the linear blocks.

Trane Donates Metal for Exo Arm

Trane Donates Metal for Exo Arm
Date: 3.13.17
Time: 9:00-10:30 AM
Location: Trane Plant #4

Trane donated some alumimum tube stock and other scrap materials for us to use on the Exo Arm Project. Mr. Pitz and myself drove over to Trane in the morning before parent teachers conferences to scout out what materials they had which could be utilized in the Exo Arm.

Special thanks to Mike Roach who took us around the plant looking for the material we needed. It was a busy time for Mike and he took time out of his day to help us out.

We found some tube stock and heavier alumimum solid stock that we thought we could use to make a hinge point. We also found some square 2" tube stock that would be helpful as well as some other assorted pieces of metal.

Alumimum dontated by Trane

Arm Test With Door Closer

Arm Test With Door Closer

Date: 3.6.17
Location: Logan HS
Goal: Test the tension and compression of the arm with screen door closers.
Students: Taren P.
Inst: Mr. Pitz and Mr. Johnston

Mr. Pitz wanted to see if screen door closers would work on the arm. He borrowed one from his Dad but the closer was pretty wore out. He then purchased two new ones that were rated for "Heavy Duty". We could not find a closing strength in pounds on them though. The closer did a nice job of making the action (up and down) very smooth. However, this needed to be counter balanced to offset the weight. The main problem was we did not feel we could increase the resistance of the closer enough to support the weight of the grinder. We could slow down the action by adjusting the closer, but that was it. We also tried to flip one of the closers around to counter the other one and that seemed to work better but still not enough. We may need to try out some spring tension here for the next test.

Bench test of door closer system. Not successful in current configuration.

Video showing the action of the arm with the closers. 

Students Experimenting with Tension/Compression Joint Articulation

Students Experimenting with Tension/Compression Joint Articulation

Date: 3.1.17
Goal: Use Vex gear to simulate different joint articulation options based on a steady cam.
Location: Logan HS
Time: 3rd hour DE class
Students: Mason, Alex M. and Vaeng

Students were given some research illustrations on different types of Exo Arm assemblies. We were attempting to scale it down and replicate the movements to determine if we could used it as a possible solution for the Exo Arm. Students used Vex parts to quickly put together a section and then used springs and rubber bands to determine resistance and tension forces.

Alex, Mason and Vaeng at work.

Measuring a spring to test on the assembly.

Spring appears to hold the assembly in a neutral position.

Testing out the assembly with rubber bands.

Testing out another assembly with springs which were cut to a specific size.