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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…

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.

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.

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.

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.

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…