Greetings, long time lurker, but first time poster here. Love this forum, and the wonderful ideas I get from here so I figured I should start chipping in. I made some sealed miniature Hall pots for a modified Thrustmaster Cougar I made for my mechpit, which I will be posting about shortly. I'm also a sailplane pilot, and have some sailplane cockpit stuff to share later too. I figured I'd start with the pots though, since it is potentially useful to more people than either my mechpit or my glider pit contributions will be.
Sealed Hall pots. I wanted Hall pots that would:
1. not be easy to disturb once installed
2. be easy to install and calibrate
6. do not collect steel shavings
All compasses pointed to sealed units. After pricing them in the wild, I decided a different approach would be needed, one that fit my budget, which is close to nothing. The tried and true bic pen method it is, (for anyone not in the know: http://www.simpits.org/geneb/?p=299
) only I decided to bring it up to date. Below is what I have come up with. The pots work great and were well worth the time it took to make them. The Ubiquitus A1302...
Currently in the classic bic pen arrangement. A1302's necessitate that I use two of the 5x5x1mm N52 square magnets I procured for this, but the sealed units use the A1301, which are identical in appearance but only need one magnet on each side since they are twice as sensitive. Only using one magnet on each side is important for the sealed pots I made because they need to fit with enough clearance to freely rotate within the footprint of the 1/2" OD of the little bearings. I was worried they would be susceptible to interference, but short of sticking a big magnet right up to them, they are dead quiet. Also completely unaffected by the presence of ferrous metals, much to my surprise.On the bench...
The little square next to the bearing is one of the magnets I'm using. Once I established the 1301's work fine with the single magnets in the bic pen arrangement, it was time to ditch that giant bearing and make something a little more elegant.Size *does matter
...sorry, but it's unfortunately true. In this case smaller is better, and there is no need for a 200kgf bearing for this anyhow. The large bearing is a skateboard bearing: 5/16 x 7/8 x 1/4 vs the smaller bearing, which are found at hobby shops: 5/16 x 1/2 x 5/32.Exploded view of the new pots
A refined version of the now classic bic pen method. These were not hard to make, and required no special tools, just time and care. My original test bearing is bottom right, and the grid is 1/2" squares for scale. The little bearings have the same bore (5/16"), but are significantly smaller. No need for a 200kgf bearing on these! (QTY) Parts [size]-price(s): *-$...
(1) Alegro A1301EUA-T -$1.50
(2) 5/16 x 1/2 x 5/32 bearings -$1.20($2.40)
(2) 5x5x1mm N52 neodymium magnets -$.50($1.00)
(1) bic pen [~1/2"L] -$...
(1) K&S Engineering brass tube [17/32 x ~3/4"] -$.30
(1) mylar disc [.030 x 1/2"D] -$...
(1) Magic Sculpt epoxy clay -$...
(3) 22ga wires/pigtail/etc -$...
(1) 9/16" brass jam nut [drilled to 5/16" bore]
*too small to calculate and/or can easily be substituted for other materialUpon closer inspection
You can see the spiraling of the threads I cut into the bic pen. I used a 1/4-20 tap and held the pen body in my hand. The 1/4-20 thread makes them very easy to mount directly to moving bits or to linkages, and is very easy to adjust/refine/tune/change at a later date.Semi exlpoded
The thing that looks like a nut is not a nut, but some hex stock I bored to 5/16", since that's the magic pressfit size for mating with the bic pen, same as the bearings. It gives me something to grab onto for indexing them or mounting them, as well as preventing the pen segment from splitting when I screw a 1/4-20 set screw into it.One of these things is not like the other
It has female threads for it to mate onto an axis that terminates with a segment of threaded lamprod. I had to use a tiny dab of superglue to keep this one happy.Hello hello hello...
Ok, not echo-cavernous, but pretty empty.3 Pin SIP, FTW!
Discs are cut out of mylar plastic, using a 1/2" hole punch. Easy peasy. Poke some holes and your good to go.5mm is juuuuust right.
This puts the sensor head dead centered with the magnets when using the bearings I did.Bend prongs thusly
...but make marks to keep orientation of wire positions. If you make multiple of these, I highly recommend bending them all in the same relative orientation in relation to the chip, to keep form hosing yourself once soldering, a trap I somehow avoided this time.Relief notches
at the bottom rim to allow the wires to pass. Note the 1/4-20 threaded stud sticking out of the pot on the left. I recommend using stainless (non magnetic) set screws for this, but this is just an aluminum threaded segment.Hemostats are a must!
Not only to hold your chip, but to act as a heatsink while soldering. There is no danger in shorting the pins together at this phase, but overheating them will kill them. Careful now!
It's really easy to disturb the wires when getting it into the recess, so be patient and work gently.Wired for sound aaaaand potted
Magic Sculpt works great to pot the bottoms. Easy stuff to work with, cleans up with water, dries in a few hours and a nice dielectric to boot.I call them ducks
The brackets are just bent aluminum stock, 1/2" x 1/16". After making a few mangled ones, I was able to efficiently make some fairly clean ones. They securely hold the pots, but allow easy repositioning if needed.Mounted X-axis...
This pot is directly mounted in the azimuth potion on my modified Thrustmaster Cougar I made for piloting mechs. The stick moves in pitch/azimuth instead of pitch/roll, and is very intuitive to aim with since it controls the upper body of a mech which moves like a tank turret. Mounted Y-axis
Current shot shows crappy wire connecting my test arms. New arms much cleaner with less holes, and now uses miniature ball linkage made for R/C gear to transmit motion and looks much nicer, but the subject today was sealed pots. The stick is it's own thing...