[mowbot] Prototype Status Report

byron nospam at cc.gatech.edu
Sun May 31 23:09:49 EDT 1998

My prototyping is progressing nicely. Cef Peterson's post gave me a few
ideas to work with. I'm just about finished gathering parts and starting
to put the first prototype together. Here's a rundown of my components:

PLATFORM: As I've said before I'm trying to keep everything dead dumb
simple for the prototype. For the platform I'm using a circular wooden
table top from a $5 tripod table. It's study enough to carry motors
batteries etc. but easy to drill and bolt to.

DRIVE MOTORS: Taking Cef's suggesting I went to the auto junkyard searching
for window wipder motors. I did think about the supposed intermittent
operation but then I though two things: 1) That wipers do work when on for
long periods of time, and 2) That they're cheap enough to replace if they
ever blow out. Of course I had no clue what I was looking for. The owner
of the junkyard let me borrow a couple of different motors to test out.
At this point I'm going to prototype with motors from Hyundai vehicles
(sorry no model number on the motor). What I liked about it is that the
mounting screws actually screw into the motor housing. I did some testing and
found that the motor draws 1A unloaded and 8A at stall (which was extremely
hard to do BTW).

DRIVE WHEELS: Standard 6 inch lawmower wheels from the Home Depot. They
fit on a 1/2 in shaft.

AXEL and MOUNTING: After searching the hardware stores for a mountable
ball bearing to pass the axel through I was finally directed to Grainger.
After purchasing bronze bearings (which do not move. That's what I get
for trying to be cheap!) I went back to the catalog and found pillow
block mounted ball bearings with 1/2 in bore (Grainger catalog #2X897).
I plan to pick up a couple tomorrow. For my initial test I plan to mount
the wheel outboard using a single bearing to shoulder the load. But I
think later on I'll mount the wheel inboard (via a hole cut through the
platform) between two bearings to gurantee that the motor has none of
the axel load on it.

DRIVE MOTOR AXEL CONNECTION: This is where I'm still a bit fuzzy. The
windshield wiper shaft ends with a screw and bolt. There isn't an easy
way to thread the end of an axel to attach it. What I've been trying to
find is a 'U' shaped bracket with a hole at the bottom to attach to the
motor and attach the axel at the top. Crude ASCII picture:


Where M is the motor, T is the threaded shaft of the motor, N is the nut,
U is the U-shaped bracket, S is the screw that attaches the axel to the
bracket, and A is the axel.

I had no luck finding one until I started writing this message. While
looking for the grainger part number, I decided to look up brackets, well
grainger has about 100 different bracket types but the one the jogged my
memory was the category battery brackets. I have a project where I mounted
9V batteries to a board. I just happen to have it in front of me. 9V
battery brackets are aluminum, U-shaped, has a hole at the bottom center,
and is about a 1/2 in wide. I plan to test these as my U-brackets in the

BATTERY: We have a battery specialty store in the area that I browsed on
Friday. The best deal seems to be sealed, deep cycle, 12V 33AH, wheelchair
batteries. Presuming I can keep my power load under 5A, I should be able
to get over 5 hours operation to a charge.

COST: Not as expensive as I thought.

Battery: $60
Motors: $40
Wheels: $10
etc: $20
Total: $150

I still need to add the cutting engine and blade and the control electronics
but so far it doesn't seem exhorbitant.

I'll keep the list posted as I make progress.

Good luck in your mowbot projects!