Recording electrical activity in behaving animals can become cumbersome when the animals spin (and trust me, they will). The wires tangle, interrupting behavior, and cause unnecessary discomfort for all involved. Commutators allow for wires to spin without tangle, while maintaining the electrical connection with low noise introduced. Active commutators do this by measuring the torque and using a motor to drive the wire to minimize the torque. There are open source systems available, but they may be overly complicated for the needs of the researcher. Passive commutators simply allow for the wire to spin on its own. If the system can spin with sufficient minimal torque, then minimal strain is imposed on the animal. Some companies (such as Doric or Dragonfly) offer expensive solutions to these problems, but their solutions often don’t allow customization for your needs and can be unintuitive and cumbersome to setup.
Herein is a modular (1 to 10 channel) system that appears to require less torque than commercial passive commutator systems (I don’t have a torque meter, but by hand it feels like less torque than my commercial system). For around $80-$150 (1 to 10 channel) you can build your own commutator system, complete with connectors. This design is based on the Passive Commutator system by Daniel Baleckaitis, Kyler Brown, and Graham Fetterman in Dan Margoliash’s lab. I added Slick to the name to be distinct from their design, but also because the acronym becomes SPEC (which, from google “/spek/ (noun) in the hope of success but without any specific commission or instructions”) which I found funny. But I do hope these instructions help. I tried other cheap systems, but they just require too much torque for this application.
Special care is given to assembly with a coaxial cable (Miniscope!!!!). A very tiny 36AWG coaxial cable (Digi-Key A9436W-10-ND) is used for these instructions. If you can make that work, you can make anything work. Of course larger wires are easier to handle.
Note: slightly older versions may appear in the pictures. The pictures herein may show a screw in front (it was a terrible idea to try to hold the bearing with a screw!) and may lack the holes necessary for the Cap. The bearing is now held with glue and the Cap.
|Moog AC2690 Slip Ring||- 1 through 10 for the number of circuits||Also see here|
|Moog AC259 Brush Block||- 1 through 10 for the number of circuits||Also see here|
|McMaster 4262T9||Flaged Bearing for 1/8” Shaft Diameter, 3/8” OD|
|McMaster 93406A040||Screw Number 1 Size, 1/4” Long|
|McMaster 90272A148||Screw 6-32 Thread, 1/2” Long|
|McMaster 90480A007||Nut 6-32 Thread Size|
|Break Away Female Headers Sparkfun PRT-00743|
|Shrink Wrap||Clear is fun||Ginsco 324 Pcs 6 Size φ1.5/2.5/3/5/6/10mm|
|Epoxy or SuperGlue (any will do)|
|Wire||Coaxial or 22 gauge single core hook up wire|
The part numbers from Moog are hyphened with the number of circuits (1 through 10), the shape of the slip rings: F for flat (don’t recommend, but it’s what I have), V for 90* groove (recommend) or R for Raised Barrier, and the platting (G for gold or S for standard (I found success with standard)). Example: I would recommend ordering AC2690-2VS (that is a slip ring with 2 contacts, the V-groove, and standard platting) and AC259-2S (that’s the brush block with 2 contacts and standard plating).
Note: Ordering from Moog can take 14-16 weeks. Plan ahead.
FDM print the passive commutator in PLA or nGen, no supports required. This part can be held on a 6 mm stereotaxic rig, or however you’d like with the given square platform. Don’t have an FDM printer? Support the ONE Core and order though us!!!! Or use an inexpensive outside 3D printing shop. Rosenberg Industries is aware of ONE Core projects and requirements and has proven success with ONE Core projects.
Why metric and imperial screws? Because that’s what I had laying around.
Take the Moog AC259 Slip Ring and slip it into the McMaster 4262T9 bearing, with the flange on the opposite side of the wires. Cut the wires to a reasonable length, maybe like a cm. Strip the wire. Cut the break away female headers for the number of channels you system will have (coaxial will have two).
Put the female headers on the wires and bend at a 90 degree angle so you can solder the wires in.
Then bend back straight.
Put hot glue between the headers and the Slip Ring.
Cut some shrink wrap to cover the assembly excessively long. It is important to push the shrink wrap down as you heat it. This will create a stop, such that the Slip Ring cannot be pushed out of the bearing.
Shrink the shrink wrap with a heat gun (hair dryer if you have to). Cut the excess shrink wrap off.
Assemble the 3D housing with the 6-32 nut and screw, the M2 nut and screw, and thread in the two number 1 screws. By pre-threading the number 1 screws and then removing them, you have set up the necessary threading in the plastic. (again, the screw that appears in front isn’t in a version you will have, please ignore)
Use super glue or epoxy to afix the bearing into the 3D printed housing. It’s a good idea to put the glue on the plastic and then place the assembly in the plastic (this keeps the glue away from the moving parts). Place the Bush Block over the slip ring (there is an orientation to the Brush Block; the side with more length between the side and the brush should face the 3D printed house).
Pull the Brush Block down and screw in place with the two number one screws. Strip the wires that will attach to the Brush Block (for the Miniscope, this will connect to the DAQ). It is easier to start with the ground wire of the coaxial cable. Try to thread it through the holes of the Brush Block at least twice. Then solder it in place. Cut any excess wires to ensure they is no shorting (probably a good time to check for shorts with a DMM). Cover the solders with hot glue.
Now let’s assemble the wires assembly to the recording device (Miniscope!). Take the break away headers and cut off another set of channels. Strip the wires and wrap around the legs of the headers. Again, it’s easier to start with ground.
Make this assembly more ridged by adding hot glue and shrink wrap. Try to make the wire centered when adding the heat to the shrink wrap. Test electrical connection and for shorts with a DMM. Here is a picture of the assembly outside of the 3D printed housing.
(!) I strongly recommend that you use pliers or something to hold onto each side whenever you connect/disconnect the system(!).
And of course it is critical to now test and verify the orientation of the polarity. After you are sure that you have the orientation correct, you can paint each side of the connector. I used my wife’s nail polish. It’s the perfect crime; she is sure to never read this, and she has little reason to suspect I would steal her nail polish.
Put the Cap over the assembly and screw in place with the Screw, Number 1 Size. This cap is much larger than necessary for the 2 circuit shown, but can immediatly accomidate the larger 10 circuit system suggested.
ONE Core acknowledgement
Please acknowledge the ONE Core facility in your publications. An appropriate wording would be:
“Engineering support was provided by the Optogenetics and Neural Engineering Core at the University of Colorado Anschutz Medical Campus, funded in part by the National Institute of Neurological Disorders and Stroke of the National Institutes of Health under award number P30NS048154.”