Now that I had the joystick fiasco behind me it was time to get down to some build time! In the previous posts I have gone through the modifications to the gimble mount, the skull mounting tabs, and some of the electrical connections that will be needed. For those that did jump on the VSA offer you are ahead of the game. If you also purchased TrackSkull from MonkeyBasic.com then you could be way ahead of the game.
Here is a little clip to show that yes, it can be done. Yes, there is still more to do. I have not constructed my servo extension yet. The audio does not sync yet. The top of the skull does not fit properly. And the software is not easy to deal with. But it will only get better from here on out.
Here are some additional build pictures. The gimble is pretty solid now. There is still one issue where if you turn to fast to the left the weight of the skull will cause the servo to over rotate and then the skull will try to spin around backward. I just have to get the left/right tab and servo arm in the right combination of position to remedy the problem. As you can see in the photos there is also a little work to do inside the skull itself. There is a chunk of plastic that will interfere with the left/right gimble tab. It will hit if you have the skull tilted forward, as if looking down, and then try to turn the prop left or right. A dremel took made quick work of the plastic.
My extensions have arrived. They shipped pretty quck. I have just not had a lot of time to spend on this the last few days. I did change the servo horn for the left/right motion of the skull. It is smoother, and does not over extend anymore. And the joystick input on TrackSkull from MoneyBasic.com is working great. They are having a sale, btw, through Aug 31 (2011).
A thought occurred to me. And I may change direction and go this route. So I wanted to share my new alternative.
Get some servo extensions. Go to a local RC or hobby store and get 4 6″ servo extensions. Cut them in half. Splice them onto the 2 ends of your 25′ of CAT5 cable. Use the wiring guide as shown in the other extension posts. It will reduce the number of connections you need to make. And it doesn’t alter the existing servo cables on the servos.
Servo <—> male end of server extension <—> 25′ CAT5 <—> female end of servo extension <—> SCC 32
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.
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.
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:
Protecting the controller from the elements
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:
Will the wire run be too long for the servos to operate properly?
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.
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.
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.