DaVaHaG - Dynamically Variable Hand Grip tension box

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DaVaHaG - Dynamically Variable Hand Grip tension box

Postby mmcginnis9272 » Tue Jun 23, 2015 11:32 am

I thought it would be good to take the advice of some and start a thread about developing a dynamically variable tension box to replace the current one for the Raptor type hands. As you can see in the proof of concept video below, a dial on the back of the gauntlet can be rotated to allow for 4 different grips.

1. normal, all finger grip.
2. precision thumb and first finger pinch
3. writing grip. Thumb and index and middle finger.
4. cup holding grip. little finger curls more to support bottom of cup.

Again, I know this is an unusable version due to the size of the cam. i am working on other methods to reduce the size of the cam box.

The .stl files are located here in ThingiVerse:

Video of the tension box in action:

Pic of design:
DaVaHaG-v1.JPG (36.15 KiB) Viewed 3031 times

Normal all finger grip:
WIN_20150620_200053.JPG (177.54 KiB) Viewed 3036 times

Cup hold grip:
WIN_20150620_200028.JPG (182.98 KiB) Viewed 3036 times

Writing or instrument hold grip:
WIN_20150620_195939.JPG (188.26 KiB) Viewed 3036 times

Precision index/thumb grip:
WIN_20150620_195931.JPG (184.71 KiB) Viewed 3036 times

View of the tension box with oversized single cam:
WIN_20150620_195912.JPG (166.98 KiB) Viewed 3036 times

Soon, I'll be posting version 2 of this box that uses 2 small cams instead of one large one to resuce the size of the box. Stay tuned......
Last edited by mmcginnis9272 on Tue Jun 23, 2015 11:55 pm, edited 1 time in total.

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Skip Meetze
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Re: DaVaHaG - Dynamically Variable hand Grip tension box

Postby Skip Meetze » Tue Jun 23, 2015 12:43 pm

This is quite a breakthrough! Well done! The large cams might not be an issue in a modular arm. I look forward to following up with you on that.

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Re: DaVaHaG - Dynamically Variable hand Grip tension box

Postby jameshs » Tue Jun 23, 2015 1:22 pm

Great idea.

I think the cam box is your way of making it happen - but what is says to me is just a linkage system that can at its simplest be de-coupled and at it's most complex be coupled/decoupled in a 'pattern'.

so if the tendon is attached to a pin, and then plugged into a peg board then it could either be plugged into the board or not - and if not then no tension when flexed, and if plugged in then tensioned as normal.

My report binder has such a system with pegs that the user pulls out or in for A4 long side or A4 short side - and this controls whether the knives slice or not when the handle is pulled.

So the idea should (by clever people!) be translated into a series of sliding plates that do what your cams do and be small and flat.

great idea!


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Jason M Bryant
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Re: DaVaHaG - Dynamically Variable hand Grip tension box

Postby Jason M Bryant » Tue Jun 23, 2015 1:46 pm

The writing instrument grip is also good for drinking from tea cups.

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Re: DaVaHaG - Dynamically Variable hand Grip tension box

Postby Gyrobot » Tue Jun 23, 2015 5:46 pm

I would like to describe a solution that is based on "Keys".

The current tensioners slide backwards and forwards in the tensioner slots individually. if we had a key that slid in through a slot in the side of the tensioner block in front of the tensioners, the profile on the "key" would limit the forward travel on each individual string. This will allow the fingers to close at different intervals. Almost unlimited key profile shapes could be printed for different grips.

Any thoughts?

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Re: DaVaHaG - Dynamically Variable hand Grip tension box

Postby mmcginnis9272 » Tue Jun 23, 2015 11:53 pm

Both of the before mentioned ideas sound intersting in their own way. I have discovered that the individual strings move just over one inch from open to closed poition. So, to prevent a finger from being activated it's string must either be disengaged all together, or its string effectivly legthened by 1 inch, thus the need for the large cam in my test setup. i just printed another version that has 2 half sized cams side by side and 180 degrees out of phase with each other. The string travels in an S pattern, under one cam and over the other. The cams are turned in the same directoin with a common gear between them. The box is now thinner but had to be made a bit longer. The problem I have is that the strings on the non engaged fingers get so loose, they fall off the cams. So, I added a guide between the two cams to keep the stringns in the grooves. We'll see how that works.

I'm not at all married to the idea of cams. I actually thing the key idea that Gyrobot mentioned could be a better way to go. A single slider on the side could be pushed in or out to any number of positions and change the position of each peg. I might play with this idea some.

I also thought about having 5 holes in a row with a string passing over each hole. If the pegs are then plunged into the holes at different depths, each peg pushing it's respective string into the hole with it, the strings could be shortened. This would accomplish the same thing. The simplest of which being either completly in or out could be held in place with the same mechanism as in an ink pen. press it down and it stays. Press again and it retracts.

My main desire is not to have the user "program" each finger separatly, but to have a cam or a key or something that has just one thing that needs to me moved that sets all fingers to a specific grip.

The final peice to this would be to have the base of the thumb on a pivot that can rotate to at least 2 positions so that the thumb can be made to touch either the top side of the index finger (like when inserting a key into a lock) or the tip of the finger (to pick up something). I know this has been tested in other hands already, but it would surely add great benefit to the overal project.

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Re: DaVaHaG - Dynamically Variable Hand Grip tension box

Postby mmcginnis9272 » Mon Jun 29, 2015 10:49 am

Here is version 2

This version is half the height of version 1 with the same effective action. 2 of the original cams has been placed side by side and 180 out of phase to each other. The finger strings run under the first cam and over the second cam. The knob is connected to the 2 cams via gears to allow the cams to be placed into 4 unique positions to cause the 4 different grips.


Here are the .stl files for those who would like to experiment with this idea:

DaVaHag2-Pic.JPG (47.96 KiB) Viewed 2933 times

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Re: DaVaHaG - Dynamically Variable Hand Grip tension box

Postby untulis » Tue Feb 02, 2016 9:25 pm

What is the state of this work?

Have others duplicated your work or the variations?

Have many recipients asked to have this capability?

Beside the added complexity of printing more parts has anyone found a reason to not implement this?

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