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Feb 9 17 6:59 PM

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Hello everyone,

I am Juan Medrano. I just joined this community since I find here a place where I really want to contribute. I would really like to contribute in a positive manner to develop affordable advanced robotics that make their users happier. I have experience with the design of battery powered systems and those using lithium-ion technology. So this is were I want to contribute. I am posting this to be able to have your (developers + openBionics) feedback, since in the first place I am not really sure this is needed :S . I have seen several other projects around affordable prosthetics but that lack an integrated/portable/practical power source, so that is where the idea comes from. This might be a barrier to remove and might be a little contribution for a wider adoption of prosthetics like the Ada Hand.

So if I may ask some (fundamental) questions:
Is there a need (ordesire) in the users for a seamless integrated battery pack?
If such a device was designed and made available, do you think Ada Hand users would use it?
I am not sure, but I understand current Ada Hand (and arm) users need a wall adapter to be power their hands?
If not, what is the current power source? 
What limitations does it have?

Unluckily I do not own and Ada Hand right now but will print one soon (I am buying parts from openBionics' shop ;D ). So I cannot measure real power consumption/peaks required.

Anyways, the ultimate goal is to develop a safe/powerful battery pack that makes end users happier. 

I come up with the following characteristics which I am guessing are desirable. Here is where your feedback to give correct shape to this is deeply necessary.

Operational time: 4 hrs (per recharge)
Number of grips per minute: 10  (how many times a person will activate (close and open) the hand per minute...(this metric makes sense at least at the power budget level)
Lifetime: 1 year
Weigth:  (450 g = 1lbs) ??
Integrated into the prosthetic ?? (not  carry on in the waist, back, etc...??). This also constrains the form factor and volume: cilyndrical matching an arm, and around the thickness of an "average arm" (what is an average arm??)
Electronic Safety Features: Primary, Secondary, Soft and Charger Protection levels. Just as background, Each protection level is independent and adds redundancy. This is what you would find in your typical laptop battery.
Mechanical Safety Features: This is were I am more in the air. So there are considerations no matter the form factor or placement of the cells, but another group of considerations arises that depend on the position of the battery pack and what conditions it will be subjected to in that position.
Features: ability to report SoC (in %) (SoC might be the more relevant, but Cell/Pack Voltage, current, temperature, cycles may also be reported ) , fully independent from the main control of the arm, plug&play, report battery decay (capacity decay).   Optional: Try to implement fast charging (50% SoC in 15 mins or so), wireless charging....(optional if are not desired right now)

Based on some information (datasheets, blog posts, Ada hand specs, etc) I tried to develop a power budget for the arm. To make it short, it seems a 110Wh pack could make the job. A good insight is that the peak power required is around 1/3 of the pack capacity, so cells can be optimized for energy storage rather than for power delivered. This means a more dense pack and weights/costs less. To use commodity cells and reduce cost, 18650 might be the option, and it would probably take 12-10 cells (there is catch there that, if the pack form factor is cilyndrical, one could pack twice more energy adding not much diameter).

Well, thank you for reading a rather long post. I hope this sounds interesting enough to have your comments.

Happy day!


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Mar 20 17 3:49 PM

Hey RobP,

No, unluckily I have not yet received any response. However, I am still working on this. I already have the mechanical elements of my hand, and just waiting for the motors. It seems openBionics run out of some components, like the Almond Board, but I think I can substitute it very well with an Arduino. I will keep the progress posted here.

Maybe you can help me out with some details? I need to know several parameters like ,for example, how many grips per minute a user performs, and to "characterize" the power consumption of each grip. I would be useful to know how you use your hand in this sense.


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