Re: Suspension losses

On 1/3/2025 11:46 PM, Jeff Liebermann wrote:

On Thu, 2 Jan 2025 12:17:22 -0500, Frank Krygowski
<frkrygow@sbcglobal.net> wrote:
 

A pair of series RLC circuits (one for the road-tire interface
and a second for the suspension-rider interface) would be a good
start. I'm not skilled enough to do the calculations, but others
on this group likely are.

>
I _may_ have been able to do such calculations 50 years ago, but I'm not
sure. I certainly can't do them now.

 Actually, the analogy between a mechanical system and RLC (resistance,
inductance and cazapitance) calculations are fairly simple.  For
example:
 "Mechanical-electrical analogies"
<https://en.wikipedia.org/wiki/Mechanical%E2%80%93electrical_analogies>
 "Electrical Analogies of Mechanical Systems"
<https://www.tutorialspoint.com/control_systems/control_systems_electrical_analogies_mechanical.htm>
 "RLC circuit: Analogy with mechanical systems."  (From Brazil)
<https://proceedings.sbmac.org.br/sbmac/article/download/134486/3384/0>

I'm pretty familiar with the RLC analogy to mechanical vibrations.
Actually, I remember sitting in a Vibrations class taught by my least favorite professor on the day he brought in a large, demonstration-sized Analog Computer (Remember those?) to model something we had been calculating. To the amusement of the students, he was not able to get the thing to work properly.

 

The hardest part is apt to be finding
an equivalent circuit for the rider, who isn't a rigid mass but
rather a dissipative blob....8-)

 If you're going to build a computer simulation, there are cut-n-paste
mechanical models of various human bodies available.
 "A mechanical model to determine the influence of masses and mass
distribution on the impact force during running"
<https://pubmed.ncbi.nlm.nih.gov/10653036/>
"Simple spring-damper-mass models have been widely used to simulate
human locomotion. However, most previous models have not accounted for
the effect of non-rigid masses (wobbling masses) on impact forces."
 Ok, a running model is not going to work well on a bicycle.  So, look
around for something that's a better fit.  I'll admit that I've never
done anything like this, but I can see how it might be possible to
model a wobbling blob on a bicycle.
 Also, modeling is NOT the hardest part of the problem.  In my never
humble opinion, the most difficult part is dealing with the large
number of significant figured necessary to maintain accuracy.  I human
or bicycle model might work accurate to maybe 1/10th of a watt, while
the power produced by a road bump powered energy harvesting system
might be on the order of fractions of a milliwatt.  This forces the
human model to be accurate well beyond reasonable limits.

My idea wasn't to model a human body for computation purposes, although others are probably interested in doing that. I'm thinking more of coming up with a physical device, perhaps for weighting a tire during a rolling drum test, so the test would more accurately reflect behavior of tires when ridden by a human pedaling a bicycle. Maybe 75 pounds of raw meat?
--
- Frank Krygowski