After cleaning up the parts their dimensions were checked and minor adjustments made so they would fit precisely into one another.
Initial assembly allowed us to mark the exact locations for the fixing screws, which were then carefully drilled through the temporarily joint parts.
The lower end of the arm attaches directly to the “wrist” motor, making it effectively a key element of its structure. These holes were also carefully marked and drilled.
The arm was then temporarily clamped to a dummy shaft to access its overall stiffness.
Finally the arm was clamped to the aluminum shaft to test its integration with the robot.
Our tests so far demonstrated that the arm requisites are being met. However the aluminum shaft on which it is clamped has proved to be too flexible causing an unacceptable degree of torsion to the whole assembly.
The voind robot design is based on a swivel arm that rotates on a horizontal shaft driven by a worm/wheel combination gear. This shaft has a very simple design with a 10mm main section and a 20 mm narrower section with 6mm diameter.
To fabricate the narrower section we decided to build a small combined Milling/Lathe machine from MDF board. This contraption basically holds firmly a small rotating tool with a small drill and at the same time allows a 10mm shaft to be fed and rotated against the mill.
After a quick test we were good to go at machining the end of our aluminum shaft. Check the actual footage below:
After the operation the machined surface shows a scaled aspect due to the manual feeding of the shaft.
But after a quick sanding with fine sand paper the result looks very smooth:
You can see below the wheel firmly clamped to the new shaft and being driven by the worm.
This aluminum shaft proved to be too much flexible. A steel shaft will have to be used instead.
One of the motors on the voind robot is an External Linear Stepper Motor, more precisely an SY17STH0404-300A6.35X2X2-P1-EX. It has a threaded shaft engaging a threaded nut that drives the robot arm perpendicularly to the equipment face.
This motor is conveniently supplied with a 30 cm shaft which should be more than enough for every application. However in our case we needed to cut the shaft shorter.
We first wrapped the motor in plastic film to protect it from any metal chips and used a small drill press vice to hold it firmly by the shaft, having wrapped it in a generous quantity of soft paper to protect the thread.
We then used a Dremel EZ456 cutting wheel to make an initial cut one centimeter outside the mark to be able to position the tool perpendicularly to the shaft for the final cut. To prevent overheating the shaft and motor we cut in 10 to 15 seconds intervals followed by 45 to 60 seconds periods of pause for cooling.
Interestingly, although the shaft seems to be made from stainless steel, not a single spark was produced during the cut…
Ideally we would have a 6.35×2 nut screwed in to help restore any damaged thread start by removing it after the cut. However we did not have any suitable nut around and we had to resort to a magnifying glass and some fine sand paper to make sure the threads started smoothly.
Finally the motor with the correct thread length and ready for assembly.