Sunday, August 4, 2013

The arm

The arm assembly

This part was done well before the bicep assembly which I have already done a blog post about but I just didn't want to risk being accused of being organized. All told the forearm and hand assembly was quite an adventure and actually continues to be interesting. The main reason for all that is that this was the first part that I tried to print and to assemble and as such has been loaded with errors that I had to correct. 

This picture show the arm, wrist and hand in the process of connecting the strings. Actually the second time I did the strings. The first time was with some waxed cord that I found at the hardware store before I had ordered the 200 lb test fishing line. It didn't work very well, hence the change. The strings lay flat across the wrist like that because I put a piece of double sided tape there in order to keep the strings in order as I pulled them in. Paper plates are an important part of my accessories. I use them for almost everything.

A detail shot of the forearm with the servo cable for the wrist servo.

This is a shot of the arm and hand when I was partway through the process of attaching the strings to the servos and the ugly knots that I was making. I was making tighter and tighter knots to adjust for slack in the strings. What I didm't realize at the time was that I had not paid enough attention to the routing of the strings. I made two important mistakes: I had gotten the strings for different fingers wrapped around those for other fingers and I had not paid enough attention to getting the pull strings on top of all possible passageways and the return strings on the bottom. The combination of these two things made trying to get proper tension in all the strings a real mess and trying to get all the fingers to pull and return mostly impossible. A bit later in the process I pulled and re-strung all the strings getting them all straightened away. I actually untied all those ugly knots using a magnifying glass and tweezers. Like I said, doing this process was a real adventure.

By the way, I had the servos connected to a Raspberry Pi by way of an Adafruit 16 servos board. The Pi that I was using was actually the control for a wheeled robot that I was playing with.

Here is an overhead shot.

A shot with all the strings attached. If you look closely you can see the confusion of strings as they enter the wrist. The problem may not be obvious unless you have tried to do the strings once. Also, you can see that three of the fingertips are pulled up. This is evidence of the problems with string tension due to tangling.

A shot of the arm during testing. The small thing with 6.2 showing is a step down voltage regulator running on the battery pack of 8 cells giving 12 volts. The index finger is flexed.

The arm assembled with Joe Walsh on the tube. At this point in the process I had already restrung all the fingers and tested the whole arm. As I discovered later there were more errors during this process that would add to my later enjoyment.

I may not sound like it at times but I am really enjoying this process. 

Next the arm, shoulder and torso assembly. And the other arm that is keeping the printer warm in my absence.

Thursday, July 25, 2013

New servo holder - better flex

After printing the newest servo holder and assembling, here is a picture. It looks better than the last version.


Wednesday, July 24, 2013

Prosthetic finger version 3 assembly

This is another version of the finger and new actuators. The actuators were redone because they were printing thicker that was intended. Here is the same sequence of pictures, extended, flexed and extended. The cutters are to hold down the servo holder.

The extend position looks good but the flex position is still short of ideal. After peering down inside for a while I found that the #1 actuator was hitting on the servo holder in the flex position causing the rotation to stop short of the end. Here are two pictures showing the flex position with the actuator #1 lower pin in place and with the lower pin pulled out.

Either some of the servo case has to go or the actuator needs a redo.


Prosthetic finger version 2 assembly and success

I printed the new versions of the finger and the actuators. There were some small problems with three parts of the fingers and the actuators printed a bit thicker that the previous ones.

This picture is of the new pieces.

I think they are much more attractive in purple.

This picture is of the bottoms of the three parts that have a first layer problem.

This one is of the assembled finger in the extended position.

... and the flexed position ...

... and the extended position once again.

Each of the flex/extend positions were done by moving the part connected to the servo base only and no adjustment of the other pieces was done. I would call that success. There is a newer version that I have not yet printed that should take care of the actuator issues and the finger layer 1 problem.

Also, I have a working servo holder/worm gear assembly that has to be mated to the 'final' version of the finger.

More to come.


Saturday, July 20, 2013

Finger assembly #4 and other stuff

Assembly test #4

Here is the info about the latest assembly of the prosthetic finger.

I printed the two new parts and they are a fraction shorter. I assembled the pieces and the finger comes closer to working but not quite.

Picture of the pieces before assembly. You can just see the little filament plug that I glued into the tip to connect the actuator to.

With the actuator on the pin.

The finger together but without the various filament pegs.

And the finger with the pegs.

Now, the flex tests. This picture is when I rotated the gear to check the flex. The tip is still in the start position.

And this one is the result if I turn the gear quickly. The momentum of the other joints flexing causes the tip to flex also. When the finger is flexed as in this picture or the prior picture, the tip joint can be moved from the straight original position to the flexed position and back but the actuator does not have enough 'pull' to keep it flexed.

Prosthetic finger servo and worm gear

While I have been working on assembling the finger I was working on getting the worm gear and servo together and ready to run the finger. I got the worm gear to run freely in the servo holder and got the worm gear mounted to the servo. I have not yet received the Corona servos for this so I am using a micro servo that I had laying around. In order to make things fit I made a 7 mm diameter 2 mm thick spacer and then glued the worm gear, space and cut down servo horn together. Tomorrow will be making the assembled bits flex the finger, hopefully without breaking any of the delicate little bits. 

Here's some pictures.

Torso mostly together

In my quest to eventually get a whole InMoov together I have gotten one shoulder and most of the torso and some odd left shoulder parts printed and together. I have a torso mount and an old broomstick connected to the end of my table with the torso mounted. I imagine my InMoov looking over to check out what I am doing occasionally.

The 3d printer difficulties have been greatly reduced lately except for a broken X axis pulley and a randomly failing extruder that turned out to be bad bearings and a pulley slipping on its shaft.

Here's a picture of the torso. You need to supply the missing head and arms in your imagination.

Well, I can see the head and arms.


Friday, July 19, 2013

Prosthetic assembly #3

After dealing with extruder problems I managed to print the new finger piece to try to get the finger tip to flex. On looking at the printed part I could immediately see that the new hole was so close to the edge that there was really not enough plastic to give the end any strength so I had to add some plastic around the hole and on the edge. The red part is the added plastic. 

The next two pictures show the new part in place with the filament pins and flexed. The addition of the new hole and pin essentially locks the tip into a non-flexed position.

The next picture shows the finger in flexed position with the new pin removed and the finger tip part manually flexed. It appears that the finger tip would need to pivot around the new hole location and the relative location of the actuator end would have to shorten in relation to that pivot location.

The next two pictures are taken from the other side in order to show the location of all the pins.

I tried to fit together the part with the new hole and the other parts in as many ways as I could but the way it is shown here was the only one that allowed all the holes to match that I could find.


Wednesday, July 17, 2013

Prosthetic assembly test #2

After Gael told me I had the first actuator upside down the assembly went a lot better. Here is a picture of it together but with filament pins still sticking out. I haven't done the servo assembly part yet.

And a picture with the finger flexed. The end joint does not flex yet. There doesn't seem to be a mechanism for making that joint move. I can see that there is a hole in the end piece without a way to insert a pin and no matching hold in an actuator. I may still have an assembly error. Important part here is that rotating the gear part flexes the finger.

Here is a shot from underneath to show where I used my exacto knife a bit to make clearance for the gear to rotate.