There are a few conditions where rotating your foot against a resistance is a desired exercise for physiotherapy.
These are usually performed using a "theraband" elastic to provide the resistance, but that is a huge pain to organise. You have to fix the theraband to your foot (uncomfortable and awkward), get the tension right, dust it with talc/chalk afterwards to remove moisture... it's just a huge pain and it requires constant concentration.
I wanted to do the exercise while lying on my back so that I could read at the same time, and have an easy-to-setup system which would also allow for progressive increase in the resistance.
The solution was to use a small weight rather than elastic, routed through a frame which could sit on a flat surface and control the angle at which the resistance was applied to the foot. For comfort and rapidity of setup, there a small socklet was made to quickly slip over the foot being exercised.
Step 1: Cut the Frame Pieces
I used a single piece of scrap 1/2" (12mm) plywood to make the base and the upright, and another small scrap as the brace.
The upright piece was cut off, then a hole to allow the resistance strap to pass through was cut. This was drawn to size and a pilot hold drilled, and then a jigsaw was used to make the opening square.
After that, the brace was cut to shape, and all three pieces were given a quick sand.
The location for the upright was laid out on the base and suitable clearance holes for the securing screws were drilled through the base.
Step 2: Assembling the Frame
Once the clearance holes were drilled, the glue was applied and then the upright was put in place. Pilot holes were drilled through the clearance holes into the upright piece and 1 1/2" (35mm) screws were drive through and pulled tight to give a close bond.
The brace was fitted immediately afterwards, excess glue which was squeezed out of the bond was removed and the piece was left for a day for the glue to cure.
Step 3: Making the Bead Bearings
To allow the strap connecting the foot to the weight to move easily, there needed to be some sort of bearing to help it chance angle.
I made a close equivalent to a roller bearing by stringing wooden beads from the craft shop onto a short length of thick fencing wire.
The hole which was cut in the upright had been sized as an integer number of beads, so once that was checked a suitable length of wire was cut.
A jig was make to bend the wire against but driving a couple of screws into a piece of scrap wood. Using a pair of pliers, one end of the wire was bent into a tight "U" around one of the screws, then the correct number of beads were threaded on and then the second end was closed with the pliers.
Note that the wire only had the second end partially closed, then the first end was unhooked from the jig, and finally the second end was closed. Without this subtlety, the only way to remove the finished workpiece from the jig is to unscrew one of the screws.
Once completed, each bearing is fitted to the upright using a small pan-head screw fitted through the loop of wire created.
Step 4: Surface Finishing
Once test-fitted, the bearings were removed and then three coats of stain and varnish were put on the piece, sanding with a fine grit between coats.
The underside of the base was only given a single coat to seal the surface as it was going to be further covered later.
Step 5: Covering the Underside of the Base
The underside of the base was covered with self-adhesive felt, mainly because the plywood on that point was fairly poor grade and it was easier to cover it than to fill and smooth it.
The piece was laid on the upturned felt, and the outline marked on the backing paper using a Sharpie (other pens are available).
I always find that when using the self-adhesive felt, it always stretches a little when being applied, so either adjust your cut accordingly or be prepared to trim off excess once it has been stuck on.
Step 6: Exercise!
Before using, you need to make the socklet adaptor. Sadly, I forgot to take any photographs when making that. I just took a old sports sock and cut it down so that it came an inch or so (25mm) past the widest part of my foot. Then I rolled a hem with a length of paracord inside it and sewed it up on the machine. Doing it by hand stitching would not take too many minutes. The webbing strap which is tied to a light weight (in this case a rolled-up towel) is then tied to the paracord.
And now you can do repetitive and boring exercises while lying flat on your back and doing something useful, like reading.
As always, do what your physiotherapist tells you, not what you read from some random block on the internet.
Step 7: Errors and "Learnings"
1) position your hole correctly! I first put mine far too high up the upright, which meant that the webbing was always trying to pull the socklet off my foot. To correct this, just meant making the hole in the upright deeper and making new (longer) bearings to run the full height of it. That wasn't a problem, but because the frame was assembled, a lot of padding and clamping was needed before the jigsaw could make the cut.
2) when making the final pinch on the wire using the pliers, be _extremely_ careful. Or else you too could squeeze the fleshy part of your fingertip between the plier tips as hard as you can. The result might or might not be a really cool blood blister like mine, but it will almost certainly be painful.