Work on Exo Arm Base Moves Forward

Work on Exo Arm Base Moves Forward

Date: 4.27.17
Location: Logan HS
Time: 3.5 hours
Goal: Fabricate a base that will support the linear rail assembly.


Work on the base has moved at a rapid pace. Based on the wooden prototype base we extracted measurements to help us determine the angles and lengths we needed to attain stability. The 3 x 3 aluminum tube stock provided a nice welding and bolting surface for Mr. Pitz and his students to build off of.

A aluminum plate platform has been bolted on to mount the linear actuator and electronics. We are concerned about the stability of the arm when moving right or left. We feel we may need to strengthen the back support or increase the base support under the platform to help stabilization. The front to back motion is well supported by a diagonal brace that was installed.

We may need to replace one of our linear bearings that mounts on the rail system. We noticed some wear and tear on it. The bearing is designed for a different type of load. We are using it in a vertical application which puts more stress on the bearing. This is not a manufacturer defect, but a result of the application we are using it in. Calls have been made to our supplier to see if a metal bearing is available instead of a plastic one.

Plate and arm being bolted to the base.

View from the back which shows the angle support and weight holder.

I know this does not look good, but the 2 x 4 just hold the arm in place until we install the linear actuator.
The arm is contracted back toward center mass and secured with velcro.

Another view of base assembly.

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Taren welding the base

Taren welding the base.

Picture of linear bearing that has experience some wear and tear toward the opening. Again, we do not feel this is a manufacture defect, but a result of the application we are using it in.

Testing Arm Movement

Testing Arm Movement

Date: 4.21.17
Location: Logan HS
Time: 2 hours
Goal: Our goal was to fabricate a mount for the warning light that will be placed at the top of the linear rail to indicate when the machine is in operation and test the arm on the linear rail.

The entire arm had to be disassembled to tighten up the gas spring bolts and replace lock washers. The spring assembly creates a lot of force on the frame which caused the nuts to loosen. Nothing fell apart, but we tightened the nuts down more. This take about an hour to disassemble and reassemble.

We also made a mount for the warning light at the top of the linear rail out of aluminum plate.

The big test was the movement of the arm when attached to the linear rail. We found the farther we extend the arm, the more force it takes to move it on the rail. When we bend the arm back toward the rail so its center mass is close to it, the assemble moves easily up and down. Also we noticed some of the small bearings that attach the mount to the arm on the linear rail came out.  We are not sure why, it could have been a burr on the linear rail when we cut it, or just the wear and tear from the arm moving up and down. We were able to put the bearings back in, but we will have to watch to see how this progresses.

We are pleased with the movement of the arm while attached to the rail system. We feel we have the spring tension very close to what we want. Movement is smooth and it does take the load of the grinder off the operator and transfer it to the arm and rail system. If you check out the video below, you will see how it moves.

Now we begin working on the base and wiring the system electronics.

Mount for light.

Mount temporarily attached to the linear rail.

Video of arm movement.

Arm Assembly and Fabrication

Arm Assembly and Fabrication

Date: 4.13.17
Location: Logan HS
Time: 7 hours
Goal: Fabricate the connection and pivot hinge points for the arm and connect the assemblies.

It took quite a while but we fabricated the hinge points and got the arm assembled in hopes of doing a test on spring strength. We are waiting for two flange bearings to finish the assembly and then mount it on our linear rail system to begin testing range of motion and functionality. Much of the aluminum raw materials had to be machined down to tolerance which took hours to complete. When the assembled arm was placed in a vice for an anchor point and tested, it appeared the gas springs were operating well and taking the load of the grinder off the operator. We will have to see once we get it mounted to the linear rail system.

Welded head tube assembly.

Another view of the head tube assembly.

Drilling the brackets used for creating the pivot points.

Brackets being measured up before mounting.

Flange bearings pressed in place.

Brackets secured in place with graded bolts.

Pivot block being drilled out for 3/8" bolt.

Center pivot point assembled.

Head assembly bolted onto arm frame.

Arm assembled and anchored to vice to test range of motion.

Another view of arm assembly.

Grinder Gimbal and Interface Fabrication

Date: 4.3.17
Location: Logan HS
Time: 2 hours
Goal: To create an interface and gimbal to allow the grinder to move multi directional freely.

Mr. Pitz worked with some students to fabricate the gimbal part of the grinder. This complex part has to allow the grinder to rotate and move up and down to grind a weld all while supporting the weight of the grinder.

Flange bearings were used on the outside edges and measurements were taken to ensure the grinder could rotate.

Concerns are in order to grind horizontally across a vertical surface the side mounts may hit the metal plate that needs to be ground down. This would cause a problem, but we don't know how severe it will be until we assemble the arm and test it. We feel right now it will effect the grinding operation minimally.

In other areas, we had concerns about the strength of the aluminum "U" bracket we fabricated out of some 1/4" tube stock. A test model was created and welded against a piece of aluminum. A 3/8" bold was used to secure it and then pressure was placed in a downward motion and then assessed. It held up much better than expected strength wise.

Test platform for gimbal prototype.

Testing the strength of the aluminum "U" bracket we fabricated out of some donated tube stock.

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