Servo Extensions Part III

So now that we know we want to use CAT5 cable we may as well begin hacking, cutting, and splicing.  In Part II I mentioned that stranded CAT5 is probably a better choice for this project.  Since I can repair my own cables easily, I am going use what I already have laying around my “lab”.  I have a 25′-30′ length of solid CAT5 wire.

I have also decided to not just add 25′ of wire to the skull.  I don’t want 25′ of wire in the way when I am setting up or taking down the prop.  So I am going add a new connection at the skull with a short piece of wire, and then connect the 25′ extension to that.  I will be using a DB9 serial connector.

There is a male and female connector for this.  Again, I am using what I have around the lab to put this all together.  So…

I will cut the connectors off the servos, and using a short piece of CAT5 cable, attach a male DB9 connector to the servos.  I will then take my 25′ piece of CAT5 and on one end attach a female DB9 connector, and on the other end I will splice the servo connectors back on.  Writing it makes it sound more complicated than it is.  The key is to make sure the same wires are connected on both ends when you are done.  My color scheme as shown below is simply what I came up with.  You can choose your own as long as it matches all the way through.

In the diagram below you will see that I am using both brown wires, and both green wires for the Red, and Brown servo wires.  This is from the discussion with Mr Chicken regarding having the wire able to carry enough power to the servos.  So by doubling up on the Brown and Green pairs of CAT5 to carry the ground and VS1 (or power) we should be able to get enough power to the servos based on what I have read on other 3-axis skull forums.

I will update this post with pictures from the build when I start working on the actual cable.

 

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Servo Extension Cables Part II

After some reading it looks like the best option is to go ahead and use CAT 5 cable to extend the servos to the PC.  There are lots of references to using lengths of CAT 5 that are 50′ or more with no issues, as long as the servo power supply is correctly sized.  Our kit came with a power supply that can provide up to 2 amps.  That should be plenty of power to push through 25-50′ of CAT 5 cable.

So what is CAT 5?  It is sometimes called UTP or Unshielded Twisted Pair.  It has 4 pairs of wires that are twisted together.  It is most commonly used to connect computers to networks.  The cable that runs from your home DSL modem to your computer is a CAT5 cable.

CAT 5 comes in different grades.  There is CAT5, CAT5e, and also CAT6.  E and 6 are more expensive.  You do not need the E or the 6.  Plain old CAT5 will be fine.  You can purchase a length of bulk cable from a hardware store or buy a long CAT 5 patch cable at someplace like Fry’s, or order one from Monoprice.  If you get a patch cable, you will be cutting the ends off anyway.

One more thing – CAT5 wire comes in stranded and solid.  Bulk wire is often solid.  Patch cords are usually made with stranded wire.  This makes them more flexible and the wire in the cable is less likely to break from being moved around over time.  So stranded is probably the way to go.  So if you do go to the hardware store, check if the bulk cable on the spool is solid or stranded.

So the next step is to figure out what we are going to cut and splice, nut, crimp, or solder, to what.

On to Part III…

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Servo Extension Cables Part I

Extending the servo cables is not quite as straight forward as it may or may not appear. In the class Mr Chicken showed us how he used a 4 pair (8 wires) CAT 5 network wire to extend the servo connections to the SCC32 servo controller board.

There are several things to consider before trying to extend the cables.

Will you house the SCC 32 somewhere safe in the prop and power it locally? If so you can do a relatively short extension to the controller and run a single serial cable, which can be up to 50′, to the show PC.  Otherwise you have to run a long CAT 5 wire from the prop to where the PC will be, and then power the controller near the PC.  This could cause problems if the wire run to the servos is too long and you get to much voltage drop between the contoller and the prop.  Your servos may not function correctly.

I have not decided yet, as I am not sure where I will be placing the prop in my haunt yet.  I can always splice more wire in place, but I would prefer to not do that if I can help it.  A 25ft serial cable from Monoprice is less than $4 (Man I love that place).

So my main concerns for keeping the SCC 32 local to the prop are:

  1. Protecting the controller from the elements
  2. Having power for the contoller (120 volts for the servo supply) So that means an extension cord to the prop.

My concerns with having the SCC near the show PC are:

  1. Will the wire run be too long for the servos to operate properly?

I need to think about this some more…

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Mounting Tabs

The L brackets that attach to the servo mount plate and the skull did not fit properly inside the skull.  The screw holes are too close to the edge of the plate.  When the L brackets are mounted to the plate and turned so they face the skull edge, they extended past the edge of the plate a little.  The plate is already a tight fit, and with the brackets not quite fitting correctly, the plate would not fit properly into the skull.  It would push the sides out a little and then the top of the skull would not fit properly.

To fix this I simply turned the L brackets around the other way and used a longer #4-40 bolt to reach the threads.

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Skull Stand

This is a simple stand I made to hold the skull in a working position on my work bench.  I make all kinds of things with the kids out of PVC pipe.  It is a material that is fast and easy to to work with, so I always have some pipe and fitting laying around.  For the main mount I just took a short piece of pipe and heated the end and then stepped on for a couple minutes until it cooled again in the flat shape you see in the picture.  I then just drilled a 1/4 inch hole for the bolt.

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Gimble Mods

The gimble mount required some modification as shown in the image below.  The primary problem was that the nut at the bottom of the gimble would come loose.  Once that happens the tab on the gimble shaft that makes the skull pan left/right comes loose.  Then it doesn’t matter if your servo is working, the skull will no longer turn left/right.

If you tighten the nut down so the tab stays in place, you can push the nylon cap nut where the other 2 servos attach off the top of the rod.  It will strip the threads out and push it off the top.

The fix was to remove the regular 1/4-20 nut at the bottom and replace it with a nylon lock nut.  I then added a new nut to the top so that I have metal pushing against metal.  See the picture for details.  The side effect is that the extra depth of the nut pushes the tab down a little.  So to get your servo arm back in proper alignment you have to let the arm out a little more.  If your little piece of all-thread is to short, you may not be able to get the servo attachment arm back into perfect alignment.

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3 Axis Skull Servo Controller Board

Here is a picture of the controller board.  The black and red wires on the left side are to the 9 Volt Battery Clip.  The 2 black wires directly below that are to the 5 Volt plug in power supply.  The connector of the power supply has been cut off, and wire striped back to fit into the connectors on the board.  The top wire has a white stripe along the side that is not visible in the picture.  Click on the image to see the full size with the annotations.

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Now what…

This domain has been hanging around for a while now so may as well do something useful with it.  I will be documenting a few halloween projects here.  The first is the latest Make & Take project from CalHauntsNorCal.  This a truly demented group that gets together once a month and does something “Halloween-y”.  Projects in the past have included pneumatic ground breaker zombies, corpsing a skeleton, make-up and silicone mold making demonstrations, lifecasting, monster mud reapers, and lots more.

The current project is a 3-Axis articulating skull.  The skull will be able to turn, tilt, and nod.  And there is a 4th servo to operate the jaw.  The build is complicated with the servos and servo connections, electrical connections, software, and programming.  I am going to try and document my efforts so that others in the group can benefit from my triumphs and mistakes.

Here goes nothing…

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