Step 7 - Mounting actuator + potentiometer / sensor
Mounting actuator, potentiometer, and sensor placement: The next step is to mount the Actuator to the arm brace and then the potentiometer (option 1), flex sensor )option 2) or the muscle sensor (option 3) - pick whichever option you chose for step 5 and 6.
Mounting the Actuator
To mount the actuator to the brace you will need to use the Chicago screws. Note you may need to use a drill bit to slightly increase the size of the holes in the brace and on the actuator so that there is little friction.
Make sure any rough edges are filed off so that the screws fit in flush.
Then mount the Actuator and screw on the tops, making sure it's not too tight.
Mounting the potentiometer (Option 1)
If you are building the potentiometer option then this is when you will need to decide where best to mount it. We tested out some approaches here but never committed to this option as a good way forward as we really wanted my daughter to control the assistive arm through her muscle signals. However during testing we simply left it loose so that she could hold it in her hand.
A potential solution could be to mount it on the forearm brace, or possibly to mount it on a ring that can be worn. Another option that was suggested to us was to use a switch instead of a potentiometer and then mount the switch on the finger.
Mounting the Flex Sensor (Option 2)
If you are building the flex sensor option then this is when you will need to decide where best to mount it. We are experimenting with her finger, thumb, and wrist. My wife sewed together a stretch fabric sock that snugly fits her thumb or finger then we simply slide the sensor in the sock.
Muscle sensor placement (Option 3)
If you are building the muscle sensor option that uses a single signal and the MyoWare muscle sensor then you should mount it in the gap of the arm brace on the bicep muscle. Here is a great tutorial that we followed to understand how to use the MyoWare muscle sensor: https://learn.adafruit.com/getting-started-with-myoware-muscle-sensor/about-emg
Clip on three wet electrodes to the muscle sensor and peel off the plastic cover. Then place it on the bicep in between the upper arm brace.
Then stick on the reference electrode to another part of the arm away from any active muscles.
Note: that this worked really well on me but not my daughter. Because of the motor neuron damage, the signal strength getting through to her arm was extremely weak and the muscle sensor was not able to pick it up out of the noise.
Note: that the muscle sensor will be worn below the clothing, while the brace will be worn over the clothing and not like it is shown in the picture.
Optional - Help build next version
The next version of the assistive arm that we are currently working on will not use the Arduino, potentiometer or the MyoWare muscle sensor but rather a series of electrodes that will provide a Raspberry Pi up to 8 separate raw signals from the limb. The onboard software will learn to recognize the unique signals being produced by the limb and use those to control the assistive device.
With this approach, we were able to consistently pick up my daughter's muscle signals! If you want to help us with this challenge please go to this page: Help Needed.
