Thread: My 3 axis skull...in progress

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Im making three of these, and other than finding a place to drill and tap a #2 screw this project is turing out to be quite easy! Thanks for putting together a great tut! Also the brass spacers look like an easy soultion as well.

Originally Posted by thedudedrummer

Im making three of these, and other than finding a place to drill and tap a #2 screw this project is turing out to be quite easy! Thanks for putting together a great tut! Also the brass spacers look like an easy soultion as well.

Let me start by saying that I have yet to fully connect my servos so there is still some open questions about any possible kinks in my setup. That said I'm pretty confident that the way I'm doing it is going to work.

You can look for local machine shops to turn the bolt on a lathe or you can do like I did, run to Lowes, buy a bunch of 1/4" x 6" carriage bolts, slap 4 or 5 nuts on them and stick the nuts in the vise and drill the end by hand. It really wasn't that hard although I don't know about drilling and tapping #2s by hand, I broke two drill bits and one tap doing the 4-40s (they broke because I was rushing, just remember to keep the drill straight, take your time and then use WD40 or 3-in-1 oil while doing the tapping and once it starts getting firm, go one turn, back it out, repeat a couple times, then back the tap all the way out, spray some parts cleaner in there, reoil and repeat until you get to the desired depth)

Like I said, I'm using 4-40 screws and I don't think they are going to pose a clearance problem and they are readily available (did a late night Lowes run and picked up some extra 4-40s). I should have my skull done within the next night or two, if you can wait a bit I'll let you know if 4-40 turned out to be too big.

I would recommend checking out some local hobby shops that do RC cars and planes, although not all shops are created equal. I happen to be extremely lucky, my LHS is owned and by a bunch of really nice, knowledgeable and willing to help people. I have lived in other areas where the people that the LHS were arrogant and generally unpleasant, just try another one if you encounter that. Mine had pretty much everything I needed except the miniSSC.

It wasn't actually the 4-40 screw that I was concerned about as far as size goes. If you use a 4-40 screw, then you will need a larger size linkage arm. Put two or three of those larger linkage arms in that tight space and they might start hitting each other limiting your motion.

I'm guessing here because I know space was tight in mine and I used smaller parts.

Please let us know how you make out with that. It would be great if space is not an issue at that size. Those screws, drills and taps are all easier to work with than the 2-56 size, so it may simplify the process.

Originally Posted by HalloweenBob

It wasn't actually the 4-40 screw that I was concerned about as far as size goes. If you use a 4-40 screw, then you will need a larger size linkage arm. Put two or three of those larger linkage arms in that tight space and they might start hitting each other limiting your motion.

I'm guessing here because I know space was tight in mine and I used smaller parts.

Please let us know how you make out with that. It would be great if space is not an issue at that size. Those screws, drills and taps are all easier to work with than the 2-56 size, so it may simplify the process.

I agree with you that the ball links themselves could pose a problem. Worst case scenario, since the loads on them are going to be relatively light, I can shave some of the nylon off to make them a little more cooperative. I already called my LHS and told them not to tap the two other bolts just in case I have to go down to a #2 screw.

I'm more concerned about the fact that my nod servo doesn't line up perpendicular to the other servos. I have a couple options for fixing it if rotating the servo doesn't bring it closer into line.

In all reality the build time for these things is relatively short once you start to see how the pieces fit together, I'd say to start from scratch again build time would probably be under 4-5 hours knowing what I know now.

Wish me luck, I'm going to try and steal an hour before dinner and get this thing together.

Good Luck! Be sure to report back. Can you take some pictures of the servos that show how they line up with each other. I don't understand how they can't be perpendicular.

Ok, so I flipped the nod servo around and the links are pretty perpendicular now. I created a new support bracket, and created a cam to mount on the rod for the pan function.

Put everything together and fired it up.

The good news is - the 4-40 ball links seem to be fine, the bad news is that something is not right with the pan linkage. Tilting the head causes it to turn when the pan linkage is attached. It was pretty late when I got to this point last night so I wasn't thinking super clearly, but I think this may be unavoidable and that the only way to correct it is to do some servo mixing.

I'm only a member of the 2 axis club at this point =/.

I'll post some pictures later today.

It's all in the alignment. If everything including the rotate servo linkage are lined up right and on the correct plain, no servo mixing is necessary.

I do not have to do any mixing with any of the 4 I made.

The answer will be in the pictures.

Originally Posted by HalloweenBob

It's all in the alignment. If everything including the rotate servo linkage are lined up right and on the correct plain, no servo mixing is necessary.

I do not have to do any mixing with any of the 4 I made.

The answer will be in the pictures.

I couldn't leave for work today without looking at this some more. I have some clearance issues that I need to work out.

The rotation when nodding is caused by the nod linkage hitting the screw connecting the cam to the rotate linkage. This should be fairly easy to fix.

I had to remove the right side of the bracket so that the arm on rotate servo could travel freely while noddind and tilting. I actually have to remove a little more of the bracket (the rotate cam still hits the bracket at the extreme nod down position), I'm just glad I created the new bracket with a hole in the middle rather than cutting out the entire middle the way you did it.

The bigger problem with unintentional rotation is with the tilt servo, I think the rotation cam has to be closer to the point where the tilt and nod ball ends connect to the rod.

Tonight I'll try moving the rotate cam up on the rod and mounting the rotate linkage from underneath but something tells me there is always going to be a little bit of rotation at the extreme ends of tilt. I also need to put some more thought into the length of the servo arms and the distance between the gimbal and the point where all the linkages attach to the top of the rod. If I rotate the skull too far to the right (skulls left) I end up passing the point of no return and when I try to go back the skull keeps rotating left, this is because I shortened the cam prior to cutting the bracket for clearance. I also need to work on my nod up, I don't get much travel that direction, I think I just have to put some thought and possibly some math into the distances.

Here are some pictures:

Top - centered


Top - nod up


Top - rotate left


Top - rotate right


Front - centered


Front - nod down


Front - tilt right


Front - rotate and nod interference

HB:

Do you recommend the LynxMotion SSC32?

I seem to be having a few problems with my MiniSSC II, I am using the VSA demo and I can't control anything other than the first two channels (I have to keep swapping the servos out to test different motions). I also noticed that occaisionally it stops responding to commands until I restart the program and it's not very smooth, setting the jumper for 90 degree range of motion helps but it's still not very smooth. I'm going to try running the MiniSSC test program but I think I'll just spring for the $40 for a LynxMotion, I figure the higher baud rate may be beneficial once I add a additional skulls to my setup.

I'm looking to do a duet kind of thing and for backup singers I'm going to do a simple jaw movement with head tilt and possibly a lift for the entire head to go up and down.

I can see by your very first picture that you need to pull your rotate linkage in closer to the center of the servo at the servo end. It is no where near 90 degrees and does need to be as close to that as possible. It looks like you will get some fighting between servos until that is resolved. The others seem to be lined up fairly well.

Keep playing with alignment until everything is as perpendicular to everything else as possible. It will start working right once you have achieved that.

You can adjust which hole on the servo armature you mount to, wether you mount the linkage on top or under that servo arm. Which servo arm you choose, and the length of the linkages. Plenty of things to play with to get the alignment right.

I do recommend the lynxmotion board. I have had no trouble with it at all. It is a great bargain at that price since it can control 32 servos instead of the standard 8 and their customer service is excellent.

I had trouble setting it up because I was confused with setting the baud rate. They talked me through it no problem and were easy to get on the phone.