Experimental Powerchair Base
4x4 - Part 1
Self built, technical
Construction details - Started on 26th April 2003
Part 1 |
Part 2 |
Part 3 |
Part 4 |
The objective was/is to
practicalities of 4x4 steering - "Tank Style", or "Skid
Steer" and see how much it rips up carpets, tyres and
how much power is consumed. I suspect it's only good for
Difficulty of making a "balancing" powerchair (like the
In so far as the basic electronics is concerned. Because
I think I can do this using Solid State "model
helicopter" Gyros, and other simple sensors and basic
how difficult it is to interface this new system, (and
Model Aircraft Radio Control since its the same thing)
with a standard Powerchairs Controller such as the Penny
and Giles one fitted to my own
ability to use this Powerchair base as both an off-road
powerchair when going outdoors with say a Recaro "car"
style seat, or as a Radio Controlled "Camera Platform"
at other times. There is no reason it can't do both!
how difficult it would be to design or build a better
powerchair. (Its just not! A trained monkey could do it
OK Part 1
the design/build! (Click an image to see a bigger
There are no
powerchair designers here! Just me and I am basically a
plumber! So what does that say about the "experts"??? God
knows. Just don't ask for any drawings. The only one I
have was on the back of a beer mat.
of all I laid out all the bits I already had, which means
the pair of ex wheelchair motors from my F55s, a new Penny &
Giles 100 Amp Pilot Plus power-chair controller from a Pride
Mobility Blast Powerchair and four brand new trailer wheels
and tyres bought from Halfords, a car part place...
I took the
two motors from my F55s Quickie wheelchair because the
things were very clunky and the motor was noisy and
"hesitant" at times... Nothing that about 10 hours work,
some new brushes, new cush drive rubbers and new gears wont
fix! But they are not "technically" available...
Still it CAN be done, I have my own ways...
wheels were 350 x 8 tubeless tyres on steel 8" x 2"
rims with four mounting holes at 115mm PCD or
107.5mm radius if you prefer. After several days
staring at all the bits a cunning construction plan
filtered in to my brain... I wanted Tank steering,
with chain drive to the wheels, simple compact and
elegant engineering construction. No yucky steel
brackets, added on bits etc, much thinking, but
little cutting!!! I chose these wheels because they
are readily available, cheap, chunky, strong,
tubeless (less puncture problems!) and I spotted
them in a local car accessory shop...
the spacers and the cross bars that join the
gearboxes together are being drilled and tapped to
M8 in my old lathe in my bedroom. The furniture
polish (Mr Sheen) makes really useless cutting
lubricant... But we use what we have The
Girlfriend is DEAD pleased! She LOVES finding
metal swarf in bed and stuck in her feet when she
gets up... Everything had to be machined alloys and
stainless steel cap screws... No bodging here... Oh
AND Cheapish! OK, enough threading and turning...
decided to check out these 3 year old "used"
wheelchair motors and look inside! They DIDN'T
look like this! First I stripped them and
tipped about 2 cups full of black burned carbon
brushes! And rust... No wonder they were a bit
hesitant, and noisy! Surprised they
worked at all... No room for anything to turn!
If you have a powerchair that sees daily use then
you must blow the dust out of the motors and
replace the brushes AT LEAST annually. If not you
are going to be stuck sooner or later. If you do
they may well last forever. A important lesson
learned. Oh, you can just see my home made Gas
Turbine's tailpipe sticking out at the top right of
the picture if you click it!
They were completely stripped cleaned in soapy
water, re-greased bearings, new brushes, and the
commutator was cleaned up with a bit of fine emery
paper. Good as new!
Gearboxes were cleaned only externally, for now, but
I will be getting new internals, and new cush drives
soon because they are clunky with lots of
backlash... These will hopefully come from Rebel
Replicas. In the meantime it will have to be noisy!
(excessive backlash from too many wheelies
previously) It will not break.
old brushes...These are a comparison, between the
old motor brush and a new one. Some were much worse
than this one on the left but I threw them out
before I remembered to get a picture...
whole project started as "something to do with all
the spare wheelchair bits" I had kicking around, and
the fact that I have a lathe in my room... Oh, and
because I can...
design had to be as "close coupled" as possible
(wheels as close together as possible) so that the
"tank style" steering does not cause problems and
its' "smooth" and controllable. Too far apart and it
will struggle to turn and tear up tyres and carpets
with my weight on it.
It was about
this time I decided that it would also make a good
powerchair base too for the street... I am a wheelchair
user! So we have a problem... And we have another problem
too! I thought I might fit a big flywheel type weapon and
compete in that Robot wars TV show! So now I need three of
these things! OR one that
will do all three jobs... We will see what happens.
I mention 4 wheel drive? Well for tank style
steering to work you need 3 things:
4 wheel drive
LOTS of torque
Wide overall track compared to the wheelbase
TaperLocks shown, allow Sprockets, Pulleys etc to be
fitted to standard sized shafts like 20mm in this
case. Extremely useful and solid fitting. They lock
onto the shaft, not needing keys or splines although
I fitted a key anyway for security.
drive chain to connect the front two wheels to the
rear ones achieves 4 wheel drive easily. These fit
using TaperLock fittings as shown
OK too much brain work, my head hurts, time for some
relaxation time So I am taking a rest.
picture shows the NEXT larger taperlock fitting sat
on the shaft as well as the sprocket one.. This one
will allow me to also fit a modified V-Belt pulley.
This pulley will have the "V" bit machined off, and
four M10 holes tapped so that I can bolt the wheel
on! Sounds worse than it is of course!
pulley is not shown here. This is how I intend to
get power to the front wheels, with a 19 tooth
sprocket on both the rear and the front wheel
shafts. These shafts are "keyed" but this is a bad
way to transfer a reversing torque load. The
sprockets (and the wheels) will all use these
"taperlock" fittings. These locate inside the
sprocket, and clamp securely on to the shaft as a
couple of Allen keys are tightened up.
Construction started! Finally Bit basic to
begin with. But the plan is in my head...!
angle bits are already drilled, and the following
pictures show how the spacers, cross pieces, and
side rails all fit together using long 8MM bolts.
The cross bits that go between the gearbox have been
tapped to take the M8 bolts.
Another view so you can see what I am talking
about... This time with the threaded bar joining
both sides. View as above - but different angle.
Now much more built!
Showing all four cross pieces, and all four side
rails fitted as well as a sprocket and chain.
A view with the bottom
aluminium plate fitted, and the wheels mounted on
the motors, with the drive sprockets for the front
This is in the wrong
place on the page! Out of sequence, blame the
Showing how the front
wheel axle and drive chain/sprocket will mount
Close up of the motor,
sprocket mounted to the shaft using a taperlock, and
the modified pulley that now forms the mounting for
those cheap wheels!
the end of the first day or part 1
More days below!
Part 1 |
Part 2 |
Part 3 |
Part 4 |