[Dprglist] Fwd: My Robot Chassis Dynamometer

David davida at smu.edu
Wed Jun 23 00:30:17 PDT 2021

Forward from Dave Ackley


-------- Forwarded Message --------
Subject: 	My Robot Chassis Dynamometer
Date: 	Tue, 22 Jun 2021 21:12:34 -0500
From: 	David Ackley <dackley at verizon.net>
Reply-To: 	dackley at verizon.net
To: 	'Anderson, David' <dpa at mail.isem.smu.edu>

Hi David

I found the email I had sent you and modified it for the DPRG mailing list.

I tried sending it via the DPRG list, but it didn’t seem to go out.

So I’d appreciate it if you would send it out to the DPRG mailing list.



*From:* David Ackley [mailto:dackley at verizon.net]
*Sent:* Tuesday, June 22, 2021 9:05 PM
*To:* 'DPRGlist' <dprglist-bounces at lists.dprg.org>
*Subject:* My Robot Chassis Dynamometer

Hi All

My “Robot Chassis Dynamometer” is what I tried to show at the 9/24/2020 
VRBNO meeting, but I’m not sure whether it ever showed up when I was 
discussing it or that people followed my description.

Just in case it didn’t show up I’ve attached a picture of the bare 
“Robot Chassis Dynamometer” and a picture of my “Build-More-Robots” 
robot sitting on it that I’m going to try tuning the PID on.

I really like the size, cost, and characteristics of the 
“Build-More-Robots” robot, so I have several different versions of it.

I decided that what I really wanted was a way of running this robot in 
place while analyzing and tuning up its  PID.

So I came up with the idea of building a “Robot Chassis Dynamometer” 
where load/inertia on the robot’s wheels is a reasonable approximation 
to what the robot would see if it was actually running around “In-The-Wild”.

In theory, the inertia that a robot’s wheels see is roughly the robot’s 
mass (Mr) times its wheel radius (Rr) squared

(i.e.~ Mr*Rr**2).

So I built a “Robot Chassis Dynamometer” with two flywheels that the 
robot’s two wheels drive that try to approximate the effect of the 
robot’s inertia.

The inertia of a solid flywheel is */one half/* its mass (Mrcd) times 
its radius (Rrcd) squared

(i.e. ½ Mrcd * Rrcd **2).

So I got a chunk of metal with a suitable mass and radius such that its 
inertia approximates my robot’s mass and wheel radius to build the 
“Robot Chassis Dynamometer” shown in the attached pictures.



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