Eric's 2-motor Walker Balance Calculator
Amaze your friends, astound your enemies!
All that's required is a browser with
I built this tool (originally) to help me salvage a
walker I built -- namely,
to figure out why this particular walker drug its back feet,
rather than walking correctly. You can use it for two
Your experience may differ, but since I developed this
tool, I use it more for the second purpose than the first...
Note that the tool is currently set up for a walker
with a single geometry (front motor shaft horizontal, rear
motor shaft vertical); I'm working on an updated version of
this tool that does not have this limitation. Note also that
the coordinate frame I use has its origin directly below the
front-leg attach point on the front motor shaft.
In order to run this tool, you just need (at least a
rough guess for) a few parameters describing your walker.
Note that this tool doesn't care what units of length you
use (inches, cm, meters, furlongs...), as long as you are
consistent and use a single unit throughout.
- Front and rear motor angles -- how far
you want your front / rear motor to rotate each way from
"zero" (i.e., if a motor's total range of motion will be
60 degrees, you'll input that motor's angle here as 30
degrees). This value is a function of the motor
you use, the voltage you're running it at, and your
circuit timing (i.e., how long you drive the motor
for in each "spurt"). I wouldn't recommend you go above
45 degrees for either of these angles.
- Foot touchdown points -- coordinates of your
walker's feet, if all 4 were on the ground at the same
time; refer to the diagram below. Note that if your
geometry looked like the "stick-figure" in my diagram,
"Xf" would be a negative number.
- Walker frame length -- distance between the
front-leg attach point on the front motor shaft, and the
rear-leg attach point on the rear motor shaft. If you're
just tinkering around, I'd suggest you use "1" for this
value (then all the other dimensions are just percentages
of the frame length).
- Front motor axis height -- most 2-motor
walkers are pretty "low-slung," so this parameter will
generally only have a small effect on balance. Still, for
As for outputs, there are three important ones, and a
couple that are available to satisfy your curiousity:
- Foremost &
rearmost extent of allowable CG
location range -- as is mentioned elsewhere,
2-motor / 4-legged walkers rely on correct location of
walker CG in order to
achieve a useful walking motion. This allowable CG
range is shown in the diagram below as a green diamond
(though, strictly speaking, you should strive to keep
your CG as close to the
walker center-line as possible).
- Percentage of frame within allowable CG
location range. As I've described in my walker
balance discussion, the larger this number is, the
less-constrained your walker design will be. But don't
get too carried away with maximizing this, since walkers
with a very high number for this value tend to tip over
- Rotated foot touchdown points -- you won't
normally care about these values, I only output them to
make it easier for me to check this tool's results.