[mowbot] Experiment in speed

Michael Davenport (michael.davenport nospam at wheatstoneenergy.com)
Wed, 2 Jun 1999 21:02:52 -0400

An experiment in determining speed for my RC lawn mower:

Walking the length of my driveway carrying a Robic stopwatch and walking at
three different speeds yeilded the following data:

"the mosey" (slowest walk) 139.8' in 48.34 sec
"the standard walk" 152.4' in 33.71 sec
"the olympic walk" 151.5' in 24.51 sec

This yeilds my walking speed for these three walks to be:
(I'm 5'9" and my legs are not disproportionately long or short)
mosey: 1.97 mi./hr. or 2.89 ft./sec.
standard: 3.08 mi./hr. or 4.52 ft./sec.
olympic: 4.21 mi./hr. or 6.18 ft./sec.

So for the following wheel diameters, the RPM will need to be:

RPM table:
mosey standard olympic
8" dia. wheel 83 129 177
10" dia. wheel 66 104 142
12" dia. wheel 55 86 118

So, it looks like I'll have to use 12" wheels in order to use direct drive
from window winder motors (I'm planning to use one at each corner) - The
ones I have seen are usually rated in the neighborhood of 100 RPM, so I'll
have to drive them from full stop to full RPM. Can this be done with PWM
signals? I should be able to get 118 from a 100 RPM motor by increasing the
voltage slightly, right?

Michael Davenport