New Print-in-Place Fingers: Three Phalanges, No Elastics

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andreas
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New Print-in-Place Fingers: Three Phalanges, No Elastics

Postby andreas » Sun Aug 09, 2015 5:14 pm

I wanted to share some old work on print-in-place fingers that I was doing in March and April that I haven't had time to take the last 15% to something for beta testing, but I think I have good proof-of-concept here.

Print-in-place fingers make a lot of sense because they eliminate a lot of assembly, parts, and in this case, knots and elastics, some of our greatest pain points. What's most exciting is that with parametric design, we can keep the termination geometry (which is high-tolerance with respect to the monofilament diameter) and the clearances between joint faces constant while varying the rest of the geometry. See here for some promising results, which I will be posting about in more detail shortly. The other interesting thing is that the "negative space" of this joint (plus the cable-routing and termination geometry) can be booleaned out of many other geometries, making this extensible to more organically modeled geometries as well.

The next step is to build the drive-able parametric model for a three phalange push/pull finger and to determine proper clearances for different machines. This dovetails nicely into another high priority project, so I hope to have some more results soon.

Fusion 360 source files
STL for download and printing, terminus cover clip here. For reference, the trimmer line monofilament is 0.053in/1.34mm in diameter, but this can be easily changed.

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Flexion via nylon monofilament
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Extension via nylon monofilament
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Summary of know-free cable termination approach in distal phalange
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Installing maintenance cover
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Maintenance cover installed
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The print-in-place joinery can be used at very small scales when the clearances are maintained parametrically
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Iterations
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Detail of internal features
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More detail on internal features
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Assembly
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skjain2
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Re: New Print-in-Place Fingers: Three Phalanges, No Elastics

Postby skjain2 » Sun Aug 09, 2015 5:30 pm

Andreas, very interesting design. What kind of Nylon are you using?

Scott Darrow
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Joined: Wed Jun 10, 2015 4:46 pm

Re: New Print-in-Place Fingers: Three Phalanges, No Elastics

Postby Scott Darrow » Sun Aug 09, 2015 7:35 pm

Andreas, Where did you source you trimmer monofilament from?

Scott

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andreas
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Re: New Print-in-Place Fingers: Three Phalanges, No Elastics

Postby andreas » Sun Aug 09, 2015 11:15 pm

I'm using picture hanging cable, which is a little finer than 0.065 trimmer/weed whacker line, but carries a 50lb load rating. See below for some sourcing options:

http://www.amazon.com/OOK-Invisible-Han ... able+clear

http://www.amazon.com/Cyclone-065-Inch- ... +line+.065

Scott Darrow
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Re: New Print-in-Place Fingers: Three Phalanges, No Elastics

Postby Scott Darrow » Sun Aug 09, 2015 11:19 pm

I printed one of these fingers at 100% scale. One joint was fairly easy to break free, and the other a bit more difficult for me. I had to clamp the finger to the table with distal phalange hanging over and tap it pretty hard to break it free.

Once I had them broke free and moved them back and forth a bit, everything moved fine. This might just be my printer, but maybe we can increase the "clear" parameter to 0.50 instead of 0.40? I am going to try and print another one at this changed parameter and see how it breaks free.

Scott
Attachments
RR 3P Finger 100%.jpg
This is printed at 100% Scale
RR 3P Finger 100%.jpg (71.12 KiB) Viewed 3539 times

Scott Darrow
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Re: New Print-in-Place Fingers: Three Phalanges, No Elastics

Postby Scott Darrow » Mon Aug 10, 2015 1:22 am

Update on parameter "clear" being 0.50 instead of 0.40 is that at the same 100% scale, I found it easier to break the joints free, and the move without sticking much better.

Scott

PeterBinkley
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Re: New Print-in-Place Fingers: Three Phalanges, No Elastics

Postby PeterBinkley » Mon Aug 10, 2015 1:46 am

Andreas!
It's great to see you're trying out thick nylon monofilament. Here's what I'm using these days:
http://catchalltackle.com/monofilament-fishing-leader-100yds-1-0mm-2-4mm-w-crimps/
The great thing about the fishing leader is that it's available in a variety of thicknesses. I've made recommendations for mono gauge for print scales from 100% (1.2mm) to 160% (1.8mm) in the Osprey assembly instructions here:
https://docs.google.com/document/d/1xbfhPYKO-4hcpnAmYpvGPY-vzPpO1QTiwvFZkcN3034/edit?usp=sharing
When you make a comfortable device for a recipient (meaning they can crank it with a lot of force without hurting themselves) and they go to pick up something heavy, you'll know why the mono is so thick. They will need it. Because of the leverage generated by the fingers, the cabling must be rated much higher than the actual lift force, or you will get way too much stretch.
That picture hanging mono is a great choice for small devices. If you stretch a wire across the back of a 50lb painting and hang it from the middle, the wire is actually under a lot more than 50lbs tension. At 1.34mm, it would have a straight rating of about 175lbs, so it's perfect for small print scales.
Peregrine used .065" (1.65mm) trimmer line on his Talon from August 2013 to April 2015, when he started using 2.0mm mono fishing leader. The "Cyclone" trimmer line you sources is a kind of star-hex bladed stuff. Peregrine just used round trimmer line. The first Ody Hand, a small child's device, used .050" trimmer line (also round) and no elastics.
https://www.youtube.com/watch?v=gM8aV6coqEE
https://www.youtube.com/watch?v=jE4xYu7EqU4
You can also use nylon printing filament, but it's only available in one size.
Attachments
NylonMono.jpg
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GreggDennison
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Location: Falmouth, KY
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Re: New Print-in-Place Fingers: Three Phalanges, No Elastics

Postby GreggDennison » Sat Aug 15, 2015 12:56 pm

Any plans on sizing these for a Phoenix Hand?

Jason M Bryant
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Re: New Print-in-Place Fingers: Three Phalanges, No Elastics

Postby Jason M Bryant » Tue Aug 18, 2015 7:54 am

I'm heading back home (and to my printer) soon. I've accumulated quite a list of things to work on for the Phoenix, but I do want to print some of these out and play around with them.

Jason M Bryant
Posts: 198
Joined: Mon Feb 16, 2015 1:59 am

Re: New Print-in-Place Fingers: Three Phalanges, No Elastics

Postby Jason M Bryant » Tue Sep 01, 2015 12:20 am

I just printed out a finger at 100%. Here are my first impressions.

Breaking the finger joints is a bit hard. I worry that I'm going to break it in a bad way.

I've been working the joints for several minutes, and they are still very stiff. I'm not sure I'll ever get this finger to move freely. I've put a lot more work into trying to loosen them up then it would take to assemble parts, and with assembled parts I can sand them when there are problems. Right now I prefer separate parts that are assembled.

I brought several types of wire back to China with me. I've got 50lbs fishing wire and some weed-wacker wire that I was planning on using with an Osprey test. The fishing wire doesn't seem strong enough and the weed-wacker wire is too big to fit in the channels. I've also got some bigger and smaller fishing wire that I got here in China, but they're not right either. Maybe the 50lbs fishing wire would work if the fingers were not so stiff in the joints.

I like that I don't have to tie knots the clip seems great so far.

Jason M Bryant
Posts: 198
Joined: Mon Feb 16, 2015 1:59 am

Re: New Print-in-Place Fingers: Three Phalanges, No Elastics

Postby Jason M Bryant » Thu Sep 03, 2015 2:24 am

Okay, I've been playing with the finger I printed a little more, and the crimping stopped working.

One issue is that the finger never loosened up. So the pulling I've been doing on the joint has been with a lot of force to try to make the finger close. However, the fingers would also have a lot of force on them anyway just to make the hand hold things, so I think that's still a fair test.

As it is, the clip will no longer hold the wire. It just slips out under any amount of force.

Could the fingertip be made to have two vertical holes? That way we could thread the wire up one hole, around a little bar, then down the other side. If you pull it back up the first hole again, the retention clip would actually be putting pressure on the wire in two places, doubling the surface tension. More importantly, the wire would also have friction against the bar that it is wrapped around.

DougB
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Joined: Thu Sep 03, 2015 9:53 pm

Re: New Print-in-Place Fingers: Three Phalanges, No Elastics

Postby DougB » Thu Sep 03, 2015 9:59 pm

Just printed the finger, after a breaking the joints free, and a short work-in, it moves freely.
Nice Job!
Doug


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