Exo Arm Work Night 5.12.17

Work Night
Date: 5.11.17
Location: Logan High School
Time: 3 hours (4-7:00)
Goal: Complete the wiring and begin building the E-Stop control circuit and delay.

Tonight we worked on completing running a different kind of conduit and pulling wires through it. This sounds easy on the surface, but we solder each wire connection in a grounded junction box, wire nut the connection and then use electrical tape over the wire nut to ensure it will not come unscrewed. The conduit is a new plastic flex conduit which protects our wiring running from the box looks surprisingly good on the arm.

Ben and Grant worked with Mr. Foye on two different circuits/boards that we needed. One to control the actuator and the other to allow the E-stop, relay and timer delay circuit to connect. This circuit is being soldered up after we tested it.

We are anxious for our next work night which will allow us to hopefully connect everything and test the system on the arm.

Grant testing his circuit.

Ben and Mr. Foye designing the timer and delay circuit.

Grant soldering a connection.

Pulling wire through conduit.

Soldering connections.

Testing the timer circuit.

Running wire through conduit.

Circuit Design Progress

Date: 5.10.17
Location: Logan HS
Time: 2 hours
Goal: Design and test the delay circuit and linear actuator circuits.
Students: Grant and Ben

We need a delay circuit for the grinder operation. We would like about a 2 second delay between when the grinder is turned on to when the operator begins to use it. This is to allow the operator to get both hands safely on the grinder. We are using a 555 timer in the circuit and used the RC time constant formula to help calculate the necessary components.

In the video below you will see when the two wires are connected (simulating a switch on the grinder) a LED will light up appoximately 2-3 seconds after the circuit is closed. This will give us the delay

The control circuit for the linear actuator has been bench tested. What you will see in the video (if you look at the multimeter to the left side of the frame) is the voltage changing as the switch is depressed. This indicates the switch we are using works and the multimeter takes the place of the linear actuator to show a voltage is sent to it. The switch also has a built in LED.

Saturday Work Day 5.6.17

Wiring Exo Arm Conduit and Control Box

Date: 5.6.17
Location: Logan HS
Time: 5 hours
Goal: Pull wire though conduit and reconfigure the control box for another receptacle with main power switch.


We needed to get a lot of the wiring done today so we can connect to the main circuit board and begin to test the electronics. Much of today was spent fabricating covers, attaching boxes, measuring wire and conduit, finding places to connect and attach everything without taking away from arm functionality.

The metal flexible conduit we saved from last years project came in handy. We tried some other types of conduit, but they were not flexible enough. This material is very flexible for a metal product. Pulling wire though flexible conduit is a challenge so we fished the wire though. The flex connectors that were used to connect to the arm and electrical boxes seem to hold the conduit firmly yet allow for arm movement. Plastic inserts were placed in the ends of the conduit to protect the wire from the sharp edge.

16 gauge wire was run through the conduit along with the power cable for the grinder. This will have to be terminated in the junction box we attached.

Control box is ready for more additions. The GFCI box was a tight fit and that receptacle is so much bigger than a regular receptacle, we had to go out the top of the box with 90 degree elbows and EMT pipe. The larger quad  box is where we will mount the relay.

Work night planned on Thursday.

Linear actuator and pipe attached to the mounting plate.

Close up of linear actuator and mounting placement. The 1/4" bolts will be replaced with graded.

The plastic control box had to be trimmed to receive the electrical boxes and wiring.

Cutting EMT pipe for conduit.

Electrical boxes mounted.

Receptacles wired in.

Getting ready to wire the grinder switch back to control box.

Hole drilled in with grommet for grinder power cable.

Box mounted on underside of arm.

Wire running through grinder arm.

Showing how conduit is attached. A metal cover was fabricated to hold the flex connector.

Arm with wire pulled through conduit to electrical box.

Exo Arm Work Night 5.4.17

Exo Arm Work Night

Date: 5.4.17
Location: Logan HS
Time: 3.5 hours (4-7:30 PM)
Students: Alex R., Alex M., Grant, Trent and Ben.
Goal: Begin to wire in the electronics for the Exo Arm.


Our goal of getting most of the wiring done tonight fell short. We spent at least an hour discussing wiring possibilities and exploring the option of a 2 second delay using a 555 timer before the grinder actually turns on. Also, part of the existing wiring for the GFCI had to be redone to allow for another switch and separate receptacle for our 12 V power supply. Regardless we made progress and have a new parts list to pick up.

The good news is the linear blocks that we fabricated (thanks to Mr. Pitz) seem to secure the arm to the rail with no deformity to the rail or block. No bearings are used in these so they will need some grease to work well.

Filing down rough or sharp edges were taken on by Alex R. and Alex M. This is really an important job because in the production of the arm we are sure to have forgotten some sharp edges so having another set of eyes go over it again really helps.

We determined that the wire gauge we will be using is 18 GA to ensure we have enough wire to carry the current without melting anything. Much discussion went into the location of the grinder switch and how it will be mounted. We decided to mount it near the grinder and then experimented with different conduit to see which one allowed for the most freedom of movement. We got some blue plastic tech conduit that we thought would work well but it did not. A piece of metal flex conduit will be used along the bottom of the arm.

The warning light at the top of the rail was wired in to a switch and tested out to perfection. The toggle switch to operate the linear actuator was tested but we could not get it to work. We suspect we have it wired wrong and need a jumper somewhere on it. The circuit for the linear actuator did not work as expected. We need to bring in a 6 V power source for it somewhere.

Work night next week will focus on more wiring and troubleshooting.

Trent stripping wires.

Alex R. filing the arm down.

Ben working with Mr. Foy on the relay circuit using transistors. More work needs to be done on this.

Filing the aluminum base.

Alex M. cutting a piece of aluminum for the grinder switch.

The newly machined bearingless linear blocks.

Trent getting some wires stripped.

Box and Panel Fabrication

Box and Panel Fabrication

Date:5.2.17
Location: Logan HS
Time: 2 hours
Goal: Begin to mount components in box and fabricate switch panel.

Our primary concern right now is the bearings on linear rail supporting the working load of the Exo Arm. We have been in contact with Schaeffler engineers to see they have a manufactured solution for us. We feel we either need to get an all metal bearing or machine out a new bearing block without a bearing in it. Special thanks to Schaeffler engineers as they are working on a solution from their end.  Mr. Pitz and Taren got to work on a new bearing block that we hope will only be needed as a backup.

The 15 amp GFCI outlet will be our fuse in the system.  That was mounted to the wall of our electrical box. We tested it and it works as advertised. We also put standoffs on our 12 V PS to keep airflow around it while it is working. This will be mounted to the side of the box.

GFCI mounted in place on box wall.

12 V PS with standoffs attached to allow for air flow.

Grant getting everything labeled on his motor control circuit.

Test block machined out to fit over the linear rail. It rode nicely on the rail, but we do not have a load on it yet.

Piece of aluminum bent up and being  drilled out  for switches.

Wiring the Electrical Requirements Begins

Wiring of the Electrical Requirements Begins

Date: 5.1.17
Location: Logan HS
Time: 3 hours
Goal: Purchase electrical parts and begin to assembly the control box.

Part of Saturday AM was spent at Menards looking for electrical boxes, connectors, wires, termination devices, wire protection...etc. We want to begin wiring the linear actuator into the system right after it is mounted so we purchased a large plastic electrical box ( we have used something similar before) to enclose all the components.

Right away we ran into problems with the thickness of the wall of the box as it was almost too thick for mounting a metal box where our 15 amp GFCI will be. We needed to modify the way we mounted the box slightly. The GFCI will be our circuit breaker instead of running a separate breaker for the system.

Someone donated a heavy gauge 3 wire electrical cord a while ago that we are repurposing for our power plug which will run into the GFCI.

Next step is to mount the 12 V power supply and then wire in a bus for our lights which also run on 12 V.

Raw materials before we begin connecting

15 amp plug attached to our wire.

15 Amp GFCI protected by a metal box and bolted to the plastic wall of our larger component box.

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.