Hi Paul.
We sometimes have real problems with switch controlled powered chairs. The
PG8 is not a problem as we have full adjustment of both forwards and
backwards bias. The DX system is sometimes incapable of adequately
correcting for straight line bias at low speeds, as the + or - 10% refers to
maximum speed. At 16% maximum there is hardly any adjustment at all. Some of
my client's would benefit from EPIC gearboxes fitted to their EPIOC motors
just so the motors are running more efficiently.
We have also found large discrepancies in the performance of motors at low
speed/power. We have built a wheelchair rolling road with optical speed
sensing and can therefore tune the no load straight line speed with some
accuracy.
Unfortunately this means nothing unless you only drive on a completely flat
and level uncarpeted floor, and your motors are both thoroughly run in. New
brushes can have a high resistance of nearly a Ohm, (depending on the
motor), until they have moulded themselves in to the commutator, (as they
may only be making contact with one winding at a time), with bearings in
good condition and tyres of the same size and correctly inflated (where
appropriate).
In practice I would expect to be able to achieve no more than 10cm lateral
error over a distance of 5 to 10 meters or so, but then most of my client's
are low speed drivers.
Finding a convenient piece of completely flat and level floor is half the
problem.
There does not seem to be anything useful in BSEN12184, you could try one
of the ISO 7176 documents, part 6 perhaps.
It also depends on the individual client circumstances. Around a domestic
house it is not much of a problem. Along the corridors of a school or
college it can be really frustrating for a client with minimal control
ability.
Good Luck.
Geoff
G.J.Harbach I.Eng MIED IIPEM
Clinical Technologist
Special Controls Service Manager
West Midlands Rehabilitation Centre
91 Oak Tree Lane, Selly Oak
Birmingham, West Midlands, B92 6JA
Tel 0121 627 1627 Ext. 53238
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-----Original Message-----
From: Paul Nisbet [SMTP:[log in to unmask]]
Sent: 11 February 2003 17:08
To: [log in to unmask]
Subject: Re: powered chair veer adjustment
Hi folks
I'm trying to get a figure for what constitutes acceptable and
unacceptable
veer for a switch-controlled powered wheelchair. This is so that
when we are
providing a chair to a client, there is a clear procedure for
testing and
adjusting veer compensation to a known standard.
I've been fiddling with DX veer compensation settings on a chair
here and a
1% veer adjustment can result in a difference of 60 cm between left
and
right wheels over 20 revolutions, or approx. 20m, which is an error
of 3%.
This suggest that this is about the best accuracy we could expect.
Does anyone know of any standards which are relevant to this? When
the
manuals say 'adjust to compensate for veer', what do you interpret
this to
mean?
Thanks for your help.
Paul
__________________________________________________
Dictated using ViaVoice Mac OS X - please allow for any errors I may
have
missed in the email!
__________________________________________________
Paul D. Nisbet
Research Fellow
CALL Centre, Faculty of Education
University of Edinburgh
Paterson's Land, Holyrood Road
Edinburgh EH8 8AQ
Tel. 0131 651 6236/5 Fax 0131 651 6234
email [log in to unmask]
http://callcentre.education.ed.ac.uk
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