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.