Electric wheelchair questions...
Hello all,
This is likely a bit off topic, but I can't think of where else to ask
this. I've recently lucked into a (working) electric wheelchair that I want
to turn into a robot base. Unfortunately, I don't know anything about them
and it didn't come with a manual. The model is an "Invacare Action Arrow".
I'm kinda hoping someone here might be able to answer a few questions about
it...
1. There's a switch on the joystick box that seems to select "Drive A" or
"Drive B". I don't know what this switch does as the drive system seems to
function in either position. Internally, this switch pulls a 5V low in one
position and leaves it high in the other. Does anyone know what this switch
does?
2. The other switch on the joystick has high, low and off positions. I
can't seem to get the chair to power up in the LOW position, although it
works well in the high position. Is it broken, or is there some trick to
getting it to power up in the LOW position? This switch was partially
broken/ wires disconnected when I got the chair.
3. The (analog) joystick outputs two (xy) control signals centered around
5.8V. These swing ~1V in either direction to steer. What is a good way to
generate these signals? Ray suggested using a DAC (that can output up to
say a 7V supply) which I think is likely a good method. Any other ideas?
Any other additional info on electric chairs in general would be greatly
appreciated, too.
Thanks, Duncan
This is likely a bit off topic, but I can't think of where else to ask
this. I've recently lucked into a (working) electric wheelchair that I want
to turn into a robot base. Unfortunately, I don't know anything about them
and it didn't come with a manual. The model is an "Invacare Action Arrow".
I'm kinda hoping someone here might be able to answer a few questions about
it...
1. There's a switch on the joystick box that seems to select "Drive A" or
"Drive B". I don't know what this switch does as the drive system seems to
function in either position. Internally, this switch pulls a 5V low in one
position and leaves it high in the other. Does anyone know what this switch
does?
2. The other switch on the joystick has high, low and off positions. I
can't seem to get the chair to power up in the LOW position, although it
works well in the high position. Is it broken, or is there some trick to
getting it to power up in the LOW position? This switch was partially
broken/ wires disconnected when I got the chair.
3. The (analog) joystick outputs two (xy) control signals centered around
5.8V. These swing ~1V in either direction to steer. What is a good way to
generate these signals? Ray suggested using a DAC (that can output up to
say a 7V supply) which I think is likely a good method. Any other ideas?
Any other additional info on electric chairs in general would be greatly
appreciated, too.
Thanks, Duncan
Comments
Some speculation:
> 2. The other switch on the joystick has high, low and off positions. I
> can't seem to get the chair to power up in the LOW position, although it
> works well in the high position. Is it broken, or is there some trick to
> getting it to power up in the LOW position? This switch was partially
> broken/ wires disconnected when I got the chair.
** Is it possible that they switched from one to two batteries in series for
hi/lo? My elec car does this. There are two battery banks, each 24 volts.
The low range uses a parallel connection at 24 volts, and a series
connection for 48 volts in high range.
Ray McArthur
>
>> 2. The other switch on the joystick has high, low and off positions. I
>> can't seem to get the chair to power up in the LOW position, although it
>> works well in the high position. Is it broken, or is there some trick to
>> getting it to power up in the LOW position? This switch was partially
>> broken/ wires disconnected when I got the chair.
>
>** Is it possible that they switched from one to two batteries in series for
>hi/lo? My elec car does this. There are two battery banks, each 24 volts.
>The low range uses a parallel connection at 24 volts, and a series
>connection for 48 volts in high range.
In every electric wheelchair I have used, they have _all_ used two 12v
batteries in series to run on 24v. They then used PWM to drive the motors.
Regards
Jean-Michel.
>Hello all,
>
>This is likely a bit off topic, but I can't think of where else to ask
>this. I've recently lucked into a (working) electric wheelchair that I want
>to turn into a robot base. Unfortunately, I don't know anything about them
>and it didn't come with a manual. The model is an "Invacare Action Arrow".
>I'm kinda hoping someone here might be able to answer a few questions about
>it...
>
>1. There's a switch on the joystick box that seems to select "Drive A" or
>"Drive B". I don't know what this switch does as the drive system seems to
>function in either position. Internally, this switch pulls a 5V low in one
>position and leaves it high in the other. Does anyone know what this switch
>does?
Purely a guess, but the wheelchair may come with two motor types;
arbitrarily labelled "A" and "B". The drive circuitry may be mounted right
on the motor, and one interface uses negative logic, and the other uses
positive logic. As I say - just a guess.
>2. The other switch on the joystick has high, low and off positions. I
>can't seem to get the chair to power up in the LOW position, although it
>works well in the high position. Is it broken, or is there some trick to
>getting it to power up in the LOW position? This switch was partially
>broken/ wires disconnected when I got the chair.
Again a guess - there may be an optional two-speed motor (indoors and
outdoors).
>3. The (analog) joystick outputs two (xy) control signals centered around
>5.8V. These swing ~1V in either direction to steer. What is a good way to
>generate these signals? Ray suggested using a DAC (that can output up to
>say a 7V supply) which I think is likely a good method. Any other ideas?
Analog is not my expertise, but I've seen comparators used as quasi-digital
gates for decision logic. I can point you to a schematic if you'd like
(least I THINK I can <g>).
>Any other additional info on electric chairs in general would be greatly
>appreciated, too.
Carl Kollar makes a GREAT motor controller board that interfaces nicely
with Stamps and PICs and was DESIGNED for wheelchair (an similar uses), and
can optionally use a joystick (or other external control) OR be controlled
DIRECTLY from the Stamp/PIC digitally with the digital interface board.
Contact me off-list for more information.
>Thanks, Duncan
Yer welcome
Bruce Bates
> >Some speculation:
> >
> >> 2. The other switch on the joystick has high, low and off positions. I
> >> can't seem to get the chair to power up in the LOW position, although it
> >> works well in the high position. Is it broken, or is there some trick to
> >> getting it to power up in the LOW position? This switch was partially
> >> broken/ wires disconnected when I got the chair.
> >
> >** Is it possible that they switched from one to two batteries in
> series for
> >hi/lo? My elec car does this. There are two battery banks, each 24 volts.
> >The low range uses a parallel connection at 24 volts, and a series
> >connection for 48 volts in high range.
>
>In every electric wheelchair I have used, they have _all_ used two 12v
>batteries in series to run on 24v. They then used PWM to drive the motors.
Just in passing - higher voltages (less amperage) have been the trend of
late. I wouldn't doubt that 48 VDC might be in future plans for smaller
mobile platforms. 90 VDC is CERTAINLY available, from MANY motor
manufacturers, INCLUDING those used in electric cards.
>Regards
>Jean-Michel.
Regards,
Bruce Bates
>** Is it possible that they switched from one to two batteries in series for
>hi/lo? My elec car does this. There are two battery banks, each 24 volts.
>The low range uses a parallel connection at 24 volts, and a series
>connection for 48 volts in high range.
I don't think this is the case. I think the switch somehow changes the PWM
logic. Perhaps there are two duty cycle ranges? Tough to test this as it
won't power up in the "LO" speed position. It's still perfectly useable
because the "HI" position can be adjusted from zero to 100% on the control
panel. This must change the upper limit (width) on the duty cycle.
Duncan
Just my 2 cents
Bruce Bates wrote:
>
> At 10:43 AM 7/8/00, you wrote:
> > >Some speculation:
> > >
> > >> 2. The other switch on the joystick has high, low and off positions. I
> > >> can't seem to get the chair to power up in the LOW position, although it
> > >> works well in the high position. Is it broken, or is there some trick to
> > >> getting it to power up in the LOW position? This switch was partially
> > >> broken/ wires disconnected when I got the chair.
> > >
> > >** Is it possible that they switched from one to two batteries in
> > series for
> > >hi/lo? My elec car does this. There are two battery banks, each 24
volts.
> > >The low range uses a parallel connection at 24 volts, and a series
> > >connection for 48 volts in high range.
> >
> >In every electric wheelchair I have used, they have _all_ used two 12v
> >batteries in series to run on 24v. They then used PWM to drive the motors.
>
> Just in passing - higher voltages (less amperage) have been the trend of
> late. I wouldn't doubt that 48 VDC might be in future plans for smaller
> mobile platforms. 90 VDC is CERTAINLY available, from MANY motor
> manufacturers, INCLUDING those used in electric cards.
>
> >Regards
> >Jean-Michel.
>
> Regards,
>
> Bruce Bates
--
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>90 volts? EVs now run a lot higher, in the 180 and 220 vdc range.
Indeed they can and do. 90 is the low range of larger, high torque,
industrial DC motors which are available to me. The higher the voltage, the
more available they are - or that has been my own experience. A simple
benchmark I use for thoughts such as this, is the TRUE (not just listed)
availability of a given motor type from TWO resources:
1. Grainger [noparse][[/noparse] www.grainger.com ] a mail order resource
2. An EV motor provider (Mohawk Distributors ??) in upper
New York State
My own needs are NOT for "legal" (able to be registered) roadworthy
vehicles, but more in the line of ATVs and like off-road use; thus, the
West Coast sources are known by me, but not generally checked due to
transportation costs. What the Big Three auto manufacturers are using, is
NONE of my own personal concern <shrug>. I generally seek surplus or used
motors for my own prototyping needs, and gauge performance accordingly.
YMMV, of course.
Regards,
Bruce Bates
mall/home or similar scenarios. If you will look in the main control
box, there is usually a set of pots. These control things such as
overall system speed, A/B overall speed, left and right turn speeds.
Sometimes these may be set too low and the unit will appear
nonfunctional...probably worked fine w/new batteries. There may also
be an A/B switch on the main control unit. If so then there may be
additional pots. If this is the case then you can consider this as a
4 spd manual transmission....ie AHigh very fast ALow Fast BHigh
Medium BLow Slow.
Good Luck!
Vince
>At 08:58 PM 7/7/00 -0400, Ray wrote:
>
> >** Is it possible that they switched from one to two batteries in series for
> >hi/lo? My elec car does this. There are two battery banks, each 24 volts.
> >The low range uses a parallel connection at 24 volts, and a series
> >connection for 48 volts in high range.
>
>I don't think this is the case. I think the switch somehow changes the PWM
>logic. Perhaps there are two duty cycle ranges? Tough to test this as it
>won't power up in the "LO" speed position. It's still perfectly useable
>because the "HI" position can be adjusted from zero to 100% on the control
>panel. This must change the upper limit (width) on the duty cycle.
>
>Duncan