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Re: Powerchair - was federated free software movement

From: Arthur Torrey
Subject: Re: Powerchair - was federated free software movement
Date: Thu, 2 Dec 2021 23:53:31 -0500 (EST)

I am not sure I understand what you mean by "references to functions of it".  
Also it is important to note that while most chairs use a common 'power-base' 
(which will vary by manufacturer / model, but functionally hardly varies) the 
seating and so on are very user specific and will vary based on medical needs, 
and the exact nature of the user's disability, as well as their physical size, 
etc.  The 'core' electronics don't change however, just the 'user interface' 
hardware and associated software.

However the electronics control system is really the only part that isn't 
effectively open in the sense of knowing how it works and being at least 
theoretically able to rebuild / replace it. (Sourcing an exact replacement 
might be an issue, but a different one)  I think that in order to be an 
effective option any control system needs to be at least as flexible and 
'universal' as the commercial systems.

I have looked at the list of projects you pointed at, and while there are many 
cool creations on it, none really seem like they would be tremendously useful 
as a source of development.  

Probably the biggest issue is lack of scale.  Where the descriptions gave power 
specs, most were on the order of 3-15VDC and 3A or less...  

A comercial power wheelchair power module runs on 24VDC and the best will 
provide drive power to two brushed DC motors at a current limited peak of up to 
120A for a few seconds and 100A for longer, although the motors will draw far 
less most of the time.  (Motors draw maximum current at stall, and minimal 
current running at speed, so rolling down the road takes far less power than 
lots of starting / stopping / turning)  This puts them into the same class as 
the controllers used in the Discovery Channel "Robot Wars" heavy robots. 
(it is also in the range of output for some welding machines) This kind of 
serious power needs a lot of serious design chops...

Arthur Torrey - <>

> On 12/01/2021 7:54 PM Jean Louis <> wrote:
> * Arthur Torrey <> [2021-12-02 03:00]:
> > I don't have much in the way of current photos, and don't see how
> > they would help much since it basically would just be 'black box'
> > electronic modules.
> In order to make free hardware power chairs provide clear references
> to functions of it. While your description gives insights, it does not
> explain functions.
> > I am a very active participant on the <>
> > website, which is probably the top site in the world for people that
> > hack on and do their own repairs of power chairs.  One of the
> > members there has created as close to an Open Source Hardware
> > control system as we have.  It is based on multiple Arduino Tinies
> > and is a very complete system, but it STILL requires a proprietary
> > Roboteq robotics controller, and a lot of very hairy scripting in
> > Roboteq's proprietary BASIC language.  The Roboteq controllers were
> > chosen because they were the only ones he could find with the extra
> > functionality for the Fail-safe / Safe-fail monitoring needed on a
> > power chair (or any other 'life safety critical' device)  It is also
> > a factor that high power motor controllers are NOT simple, as a lot
> > of the 'minor' things that get mostly ignored in basic electronics
> > become major factors.  Even so I'd love to attempt doing one of
> > those setups, except for the estimated $1-2K cost...
> That is one step forward in understanding what you would need.
> Here is list of free hardware Robotics devices which I have not verified,
> could be non-free as well:
> Feel free to provide link to instructions of that wheel chair which
> will tell about its functionality.
> -- 
> Jean
> Take action in Free Software Foundation campaigns:
> In support of Richard M. Stallman

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