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Aug 11 16 10:08 AM

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PROBLEM
The Ada hand has limited mobility for grasping objects, particularly when used as an end-effector to a system that does not have a wrist.

CHALLENGE
To make a powered wrist for the Ada hand capable of getting into the correct position to best grasp a variety of objects.

REQUIREMENTS
1. The solution must give the hand flexion, extension, adduction, abduction, supination and pronation (standard 3DOF wrist movements).
  • Different hand positioning is required to grasp different objects, without all of these movements, the hand wouldn't be able to get into position for some objects.
2. The solution must not increase the number of control inputs (still just one USB cable).
  • The Ada hand needs to be simple to control so it can be used by a lot of people.
3. The solution must be compact.
  • If it's to fit onto an existing arm, it must be as small as possible so as not to elongate the arm unaturally.

SUGGESTED BRIEF
Develop a 3DOF wrist to connect the Ada hand to. Use the control output pins from the Almond PCB to control the wrist motors (which would need their own circuitry). You could look at a few different wrist configurations, such as a stewart platform or a gimbal arrangement. Motor selection will be key, and stepper motors, brushless and brushed DC should be considered. The wrist will need to take a very large load but will not necessarily need to have a lot of force and as such a clutch type mechanism to move load off the motor gearbox onto might be worth considering.
 
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#1 [url]

Oct 11 16 7:55 PM

It is written that "The wrist will need to take a very large load...." 
Is there any defined load for the application? It would be helpful if you have numerical value determined or just assumed one from the observations. 

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#2 [url]

Oct 14 16 12:17 PM

Hi Koralp, 

With this sort of thing it's hard to specify a value becasue as far as the user is concerned stronger is always better. We're playing catchup with nature. However, in this instance I think assuming a hand payload of 5 kg is a good starting point; that's a heavy bag of shopping. This should allow you to work out the strength requirements for a wrist. Imagine both the case where the load is being held down by someone's side (an axial load for the wrist), and when they're holding it with an extended arm (bending across the wrist). 

I hope this helps, 

Jonathan. 

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