Sorry for
the long pause in my blog … times are busy, and I had to put the
TreppenSchlepper project dormant for months. Let's hope there is more time
available during summer.
After a
lot of trying and some hints from HOTINT support in Linz (thanks, anyway!) I
still haven't been able to finish a first but useable version of a
TreppenSchlepper model. Maybe the task is somehow a mismatch with HOTINTs
original goal, or (more likely) it's me being no mechanical engineer. However, it
just didn't get me to a point here the basic kinematics of TreppenSchlepper
moving up a single step are simulated. So it might be time rethink strategy,
better define what we need, and look for alternatives.
So, what are we looking for exactly?
In order
to design a TreppenSchlepper, a model capturing
its basic mechanical behavior would come in handy
Why? So
we can…
- verify a mechanical design (e.g. to check if a certain geometry and setup is safe from tipping-over going up different types of stairs)
- calculate basic stuff like the energy required for a specific stair, as well as forces and torques to further specify the components
- use it in a next step, to test the control software to be developed (environment identification, path planning,…)
The idea
is to simulate basic static and dynamic aspects
in a mathematical simulation, which can be used to develop the main parts (see this article) in
parallel and independently, without having to invest into building up real
(physical) prototypes
Maybe
even a 1D simulation (z-axis) would be sufficient to get a first, rough idea.
We could already use it to estimate what the (lifting) actuators need to do,
and thus power consumption, timing, and energy storage requirements.
Adding a
second dimension (x, z) allows to start developing the control mechanism with
path planning etc.
Finally
we need to go 3D, and add environment models (ground, stair), This will allow
fully functional simulation of the whole system, and (together with some
rendering) allow to produce nice movies.
So maybe just start over, fire up MATLAB, and start with a 1D simulation and see where we
get?
The most simple model might be comprised of just…
4 objects
That
would be
- Foot_plate
- Outer_shell (includes payload mass as well)
- Floor
- Actuator (piston between foot_plate and outer_shell)
With each
part defined by its parameters (dimension, mass, potentially spring-constant)
Next, a…
Representation of the stair
is
needed. While there is a great variety in stairs, they do follow a fairly
common design principle, explained in the picture below.
Assuming
a human step length of 63 cm, ideal stairs should be sized like this:1 x
tread_depth + 2 x rise_height = step-length = 63 cm.
This is
why 18/27 stairs are so common, with 18 cm rise height and 27 cm tread depth.
Eventually
we would of course need all 3 dimensions, see this
blog. Might be nice to collect a small library of typical and interesting
stairways which can be used to test TreppenSchlepper models and even more so
its control software to come.
