7/24/14 New Game Plan, Another Modular Tensioner Design

Today Alex and I came up with new goals to have done by the time this program ends.  First, we should have a working model of the Modular Beast and at least one attachment for it.  For now, that is primarily Alex's job.  Our next goal is to have a printed model of our version of the RIT Derek Arm.  We plan on applying splayed fingers and variable grip to it to make it more effective.

I looked on e-NABLE for ideas about variable grip.  The two best options I found were made by David Orgeman and Steve Wood.

Steve Wood tensioner balancing design

 I decided not to do this one because the strings get bunched together and tangled inside the tubing.  I'm afraid this would cause more problems than it is worth.

Orgeman spring design

Instead I have decided to adapt the above Orgeman design. By adding springs to the existing tensioner variable grip is achieved in a very consistent and simple manner. This has the down side of requiring non-printed springs but we believe that the benefits outweigh the cost.

As with yesterday I (Alex) continued to try and find a way to make the modular tensioner work. As I feared, the pins had a tough time printing and when I printed with PLA instead of ABS plastic they had nowhere near the flexibility required. After talking to Frankie about this problem we decided to adopt a design inspired by the bearing belt guide from a RepRap 3D printer.

My new modular tensioner design

This friction fit design is very simple and easy to print while still remaining strong. A few modifications will need to be made to prevent the tensioner assembly from rotating but overall I really think this could be the final design.

That's all for today, we have a field trip with our other undergrad research students tomorrow so we won't have anything new to post. See you next week!

Alex + Sam

7/23/14 RIT Arm Editing and Printing Pins

I spent today in Inventor with the Derek Arm.  Improvements were made in all the pieces except the fingers and knuckles.  First, I fixed up the trouble with the thumb tube in the palm by making the curve less extreme.  All it took was some quick dragging of control points.  Now the string should be able to tread through with less resistance.  Hopefully this helps with the lag in the closing of the thumb.  Next, I made the tensioners square.  After that, I edited the gauntlet to accept the new shape.  Here are some screenshots.

I put some holes through the gauntlet to reduce the amount of material used as well.  It should hold up just as well as it did with all the excess material.  

I decided to do the same for the forearm cuff, however, I'm not sure how it will turn out.  

I'm hoping to do a bit more editing with the arm tomorrow.  Then, I plan on printing it to show what Alex and I have done to improve it.  However, I don't think putting a few holes in it would make it worth printing another arm.  

I'll have to do more work on improving the overall functionality of the arm.  While I think it works fine now, we should do some brainstorming to see if there's anyway to make it better.  For example, the shape of the palm works, but it doesn't seem right to me.  I think we should come up with a better shape for it. We should also consider ways we can use the palm to get better grip out of the hand.  Maybe we can use the space inside the palm or pipe to apply the variable grip mechanisms.  Maybe the palm itself can slightly to better grip the object.  Maybe adding another thumb on the other side would help grip.  

I would like to make the first pair and second pair of fingers closing time be slightly staggered, splayed, and closer together as well.  In order to do this and make it effective, I think the arm needs variable grip. I'll come up with some sketches for that tomorrow hopefully.

While Sam was working in Inventor I spent my day in Rhino trying to sort out our modular tensioner problems. After searching around the web for awhile I decided to try a snap pin design similar to the pins used in the Cyborg Beast fingers. I already had one of these pins drawn up from when I was working with the Cyborg Beast earlier so all it took was some clever extruding and scaling.

My new pin design (shown in green)

Printing pins vertically like I have drawn above can sometimes be problematic but hopefully with some supports the print will turn out okay. Further testing on this will be conducted tomorrow.

Well that's all for today!

Alex + Sam

7/22/14 Inventor, Fusion 360, Modular Tensioner Problems

We finally got around to installing Inventor today!  I spent the day re-familiarizing myself with the Inventor while Alex continued work on our modular tensioner idea.  After fixing, printing, and refixing, we determined that the prongs are not flexible enough to be used here.  If they were longer, it might work, but that would significantly increase the size of the tensioner housing.  Tomorrow we shall discuss other solutions.

A example of how the prongs continue to break.

Meanwhile, I began work on editing the RIT Derek Arm.  So far I removed material from the Triceps Cuff to make it a bit cheaper (less material = less $$$).  Tomorrow I will probably do the same with the forearm cup.

Today we also published our modular tensioner idea to the e-NABLE community which received a very positive reaction. I (Alex) spent the majority of my day trying to come up with ways of beefing up these clips while maintaining flexibility but in the end I believe we will have to find some other type of clip.

One of several concepts I drew up today to try and beef up the prongs (sadly this didn't work)

The e-NABLE community is pushing hard for all designers to use a single program, Autodesk Fusion 360, so we spent some of our day installing and playing with this program. Fusion 360 is cloud based so it didn't run nearly as smooth as Rhino does. This combined with a more constraining (as opposed to the more free flow Rhino gives you) led to a negative reaction towards Fusion 360. The program appears to be very powerful but I just don't know if we will be able to break our Rhino habits and get into using it.

Well that's all for today!

Alex + Sam

7/21/14 Frankie's Day Off

Frankie isn't here today, so Alex and I are working mostly alone.  I have to admit, we got less done without him.  After spending an hour or so working out the size issues with the mid gauntlet and tensioner housing, I wasn't sure what else to do.  Alex and I decided to start work on redesigning the RIT Arm, but we realized we didn't know enough about Rhino to be able to do anything significant in a reasonable amount of time.  Because most of the original files for the Arm are Inventor files, I would love to begin editing the Arm in Inventor, but we are still waiting for the licence to be renewed.  After that, the real progress can begin.  We found ways to stay busy today, but we accomplished less than I would have liked.

The new and improved Mid Gauntlet with some sizing issues that were ironed out.

7/18/14 Modular Hand Additions

After posting our video about the modular hand last night, we received feedback about how to easily replace the strings.  We thought of this roadblock a while ago, but we decided it was time to confront the problem.  We decided to use the same snap fittings to be able to move the entire 'tuning block' from hand to hand.  Here's a prototype we drew up and are in the process of printing.

Here's the piece we printed today.

This part houses the tensioners.  The rectangles act as the female part of the link.  The male parts come out of the gauntlet.  This set up will keep the fitting from going inside the gauntlet and interfering with the wearers arm underneath.

The mid gauntlet finished printing today as well.  However, the female half of  the fitting is slightly to small for the male half.  And the walls of it are too thin.  With some tweaking, the mid gauntlet should be ready to go.

Someone mentioned the durability of these fittings.  Right now we are printing the prototypes in ABS, however, the male part isn't as flexible as we hoped.  To overcome this, we plan on printing in nylon to get more flexibility and durability.

That's all we have for today.  Join us next week when we finish the Modular Hand and maybe start another project!

Sam and Alex

7/17/14 RIT Arm Complete and Durability Tests!

Today was spent doing the final stringing and tensioning of the RIT Arm.  Overall, the arm works pretty well.  The only part that still sticks is the thumb.  It's sanded well, so I figure the thicker string is having trouble moving around the sharp curve in the thumb tube.  We'll have to work that out in the redesign.  We also changed the elastic bands of a few fingers to get them to the same tension of the rest of the fingers.  Here are a few pictures of our completed RIT Arm.

After finishing off the arm, we decided to do durability tests on the Cyborg Beast.  This included dropping the hand onto concrete from one story, three stories, and down a long stairwell several times.  The hand did very well in the drop test.  The only damage was in the cracked rails on the gauntlet that hold the Velcro in place. We aren't surprised they broke because the rails were very thin.  A few small modifications could beef it up.  Otherwise, the hand only suffered scuffs and a loose tensioner occasionally popped out.

After the drop test, we simulated a harsh environment by sandblasting the hand.  Sand got in all the joints and gummed up the entire system.  This was expected.  Any joint system would get stuck, no matter what it was made of.  Rinsing off the sand got the joints mostly unstuck.  At the same time, we learned that the Velcro straps work when wet.

We also printed the palm for the Modular Gauntlet and a test block.  Surprisingly, the snap fit actually worked!  I was expecting the prongs to break of the ABS to be too rigid but it worked great!  We posted a video about it to e-NABLE (https://plus.google.com/communities/102497715636887179986) and will eventually apply the slots to our mid gauntlet!  Yay we're contributing!

That's all for today!

Alex + Sam

7/16/14 RIT Arm Stringing, Handomatic

The RIT fingers finally printed!  We started off the day by sanding the fingers.  Then, we assembled the hand.  Turns out the thumb sticks because of the mess up with the knuckles.  We will probably reprint in.  In order to string the elastic bands, we mocked up and printed 10 small beads (printed in red) to anchor the strings.  Tying the knots was a pain because we didn't know how tight it needed to be, however, we learned it was fine.

Stringing of the elastic bands

Stringing the white strings was much more difficult.  Because the hand was designed for fishing line, the thicker string wouldn't easily go through the holes in the knuckles and palm.  First, we tried using a thin copper wire to pull the string through.  Even the copper wire was too thick for the holes, so we used a light weight fishing line to pull the string through.  This worked beautifully...until we reached the thumb.  As it turns out, the hole that feeds the string from the thumb to the palm has a sharp turn in it.  The string would get caught on the corner, then the line would snap trying to pull it through.  After quite a bit of work and jimmying of the string, it was finally pulled through.

The RIT hand after pulling all 5 strings through the fingers (the strings are white above)

The tensioners printed!

As a result of our struggles stringing the RIT hand, we reached several valuable conclusions about stuff we definitely need to change.

1.  Replace Chicago screws with 3D printed pins

2.  Use less material by making the pieces more "wireframed" (the tricep mount and elbow socket don't need to be solid pieces)

3.  Round the curve in the string tunnel from the thumb to the palm as discussed above

4.  Get rid of beads by adding holes in the palm to tie the elastic bands through (similar to Cyborg Beast design)

5.  Add silicone sleeve around elbow socket

6.  (I'm sure we'll find more problems)

We weren't able to complete assembly today but tomorrow we should be able to string up the tensioners and have a completed arm.

While talking to Frankie today I (Alex) found out that there is web based application created by the e-NABLE community known as Handomatic that aims to allow people to use a web interface to create hand models for printing. This application is still in development but I plan to investigate and possibly contribute code to this project.

Handomatic which is still in development

Hopefully tomorrow we will be able to finish the RIT arm and get back to working on more Cyborg Beast designs, but that's all for today!

Alex + Sam