Thread: Moving Arm Mechanism for 3 Axis skeleton?

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I have some other images showing more detail of the bracket which holds the twist and shoulder servos.

Keep in mind that the servos shown in these pictures were the cheap knockoffs used in the prototype and have been replaced with higher quality Hitec servos as listed above.

Here is another view of the rotate and shoulder servo

http://halloweenbobshaunt.com/Arms/15.jpg


This is the Bracket that holds the arm to the skeleton as seen from the front:
http://halloweenbobshaunt.com/Arms/16.jpg

Here is a closeup showing how the elbow servo is attached to the shoulder rod which runs through the hollow Barney arm and is attached to the shoulder servo at the top:
http://halloweenbobshaunt.com/Arms/17.jpg

This next picture shows the metal block that attaches to the tabs on the large Shoulder servo and hold the shoulder rod that runs through the hollow Barney arm. The angle it is mounted at is determined by how it sits on the shoulder blade so that the arm hangs down straight while at rest.
http://halloweenbobshaunt.com/Arms/18.jpg

This image shows how the rotate servo attaches to the shoulder servo. This image is from the chest looking out at the arm. At the bottom of the shoulder servo, you can see one of the screws which hold the metal block to the servo. This is the opposite side from what you saw in the previous picture.
http://halloweenbobshaunt.com/Arms/19.jpg

Finally, this shows the bracket which holds the twist servo which attaches to the bracket that attaches the entire arm to the shoulder blade. You can also see how the Shoulder servo attaches to the twist servo pretty well here. This shot was taken from behind.
http://halloweenbobshaunt.com/Arms/20.jpg


Hopefully some of these close-ups will help

They worked OK for the arms.

They had enough torque, but the failed too often for me.

Of course, for the price, you can buy about 5 of these for each Hitec, so having replacements around is easy, but no fun if it goes down in the middle of a show.

It's all about reliability.

That much torque is not needed anywhere in the skulls.

Originally Posted by snake-byte

Bob,

How have those MG995 servos worked out for you? I bought a small batch to try them out and I think that they seem to work really well. The one thing that I did was I opened each one up and hot glued the 3 wires to the circuit board. I've read that this is the weak point for these servos. I do like how much torque these servos have. Also, do you use these servos inside your skulls or do you prefer a different servo with less torque?

Great work on these skeletons!! Can you figure out how to make them walk?

All the parts are custom made.

Don't take any of the parts that I made as the only way to do it. I used material I had laying around. It does not indicate that the thicker aluminum was needed for structural support. It was just what I had around. I'm sure my designs can be streamlined as well.

I hope the other detailed pictures I posted help.

Originally Posted by Halstaff

Bob, those are great and answer a lot of questions. And quick too!
However, I'm still not sure of the different brackets that make up the shoulder joint. It looks like you're using a combination of 1/16 and 1/8 inch aluminum for those. I assume you had to custom make the elbow joints?
Steve

Perfect Bob! That really clears things up.
Have you had any experience with these heavy duty servos from Futurlec - http://www.futurlec.com/Servo_Motor.shtml ? They look like they have around the same amount of torque and all metal gears for less than a third of the price of the Hi-Tec.

If you're not into fabricating parts, the arm assembly I made is assembled out of off the shelf componets. There is very little fabrication required. I posted a parts list awhile back if there is any interest I'll see if I can find it and repost.

However if you like tinkering and designing then cut, bend and saw away!

Originally Posted by Halstaff

Perfect Bob! That really clears things up.
Have you had any experience with these heavy duty servos from Futurlec - http://www.futurlec.com/Servo_Motor.shtml ? They look like they have around the same amount of torque and all metal gears for less than a third of the price of the Hi-Tec.

I have not seen these before, so I can't comment on how reliable or quiet they may be, but their Heavy Duty 180o Servo Motor has close to the same torque specs as the HiTec HS985MG. They might be worth a look. The price is right.

Originally Posted by scareisburg

If you're not into fabricating parts, the arm assembly I made is assembled out of off the shelf componets. There is very little fabrication required. I posted a parts list awhile back if there is any interest I'll see if I can find it and repost.

However if you like tinkering and designing then cut, bend and saw away!

I would like to see the parts list if you could find it. Would these work http://www.servocity.com/html/standa...rvoblocks.html there is a video of the blocks in action. I can make a lot of stuff, but sometimes it is easier to purchase the parts. Trying to find time to work on fabricating is hard to find right now.

Originally Posted by Hobie14T

I would like to see the parts list if you could find it. Would these work http://www.servocity.com/html/standa...rvoblocks.html there is a video of the blocks in action. I can make a lot of stuff, but sometimes it is easier to purchase the parts. Trying to find time to work on fabricating is hard to find right now.

Post #15 Animated 3 DOF Arm

Originally Posted by scareisburg

If you're not into fabricating parts, the arm assembly I made is assembled out of off the shelf componets. There is very little fabrication required. I posted a parts list awhile back if there is any interest I'll see if I can find it and repost.

However if you like tinkering and designing then cut, bend and saw away!

This is an excellent job and perfect for arms that might be covered in some way with clothes.

It looks like the mechanics are bulkier and more difficult to hide if the entire mechanism is not covered.
Although mine does have exposed parts they are not all that visible from a short distance away, and everything is mounted on a regular Bucky skeleton.
My goal was to make something that could be mostly exposed and not give away the mechanics of how it was done.

Originally Posted by HalloweenBob

This is an excellent job and perfect for arms that might be covered in some way with clothes.

It looks like the mechanics are bulkier and more difficult to hide if the entire mechanism is not covered.
Although mine does have exposed parts they are not all that visible from a short distance away, and everything is mounted on a regular Bucky skeleton.
My goal was to make something that could be mostly exposed and not give away the mechanics of how it was done.

Your correct Bob, my goal was to build something with the least amount of fabrication and using off the shelf parts. The biggest part is the shoulder rotate, I used a servo city gear assembly, I wanted to make sure to have enough torque to lift the arm at full extension including a hand and arm bones. I like your design for the shoulder rotate, I might be able to adapt it to use standard lynx motion brackets and get rid of the big gear box.

The plan was to make it programable using realtime motions. I made a master arm that controls the slave arm, but have not done much more then that. Need to work on the computer interface and make the other arm. Monkey basic was the program I planned on using. Perhaps some day when the moon (money) sun (time) and stars (desire) align it will happen.