Re: [mowbot] blades, drives

Lawrence Lile (lilel nospam at
Mon, 3 May 1999 14:01:49 -0500

I'm designing around 5 RPM, and a 10" wheel for a real turtle of a mower.
Others are looking at faster speeds. I'm planning on a more continuous

I'm curious about other's experience with the plastic trimmer blade
converters. Most people seem to end up with the disk and razor blade
concept for a trimmer. I'm afraid of that - if the plastic swing blades
work they should be safer. I have a friend that lost a hand in a mower.....
What "didn't work" about the plastic blades?

I'm putting together a custom transmission. I've got some 6000 RPM motors
with worm gears on the shafts, bought some nice cheap little nylon gears at In a couple of stages I can gear it down to 5
RPM. The last stage is a chain drive to adapt to my wheel shafts. The
wheels are hardware store lawnmower wheels.
Idling current of the motors is 60mA, locked rotor is something less than an
amp. I figure the torque will be immense (probably limited by the plastic
gears, not the motor) becasue of all that gearing down. Ought to be able to
climb a molehill, at least.

-----Original Message-----
From: adamdb nospam at <adamdb nospam at>
To: mowbot nospam at <mowbot nospam at>
Date: Monday, May 03, 1999 11:52 AM
Subject: Re: [mowbot] test

>On Fri, 30 Apr 1999 19:43:53 -0400 (EDT) byron nospam at (Byron A
>Jeff) writes:
>> > Drivetrain: Two car power window motors with worm gear.
>> Same. Center mounted so that the circular body can spin on its axis.
>> I did most of my drivetrain work last spring. Learned quite a few
>> things:
>> BTW I'm using a couple of Hyundai WW motors....
>What kind of RPM do these generate? The ones I saw at
>operated at 100RPM. Figuring for 6 inch wheels (approximately 18 inches
>in diameter) that would give a speed of 2.5 feet per second
>(approximately). This seems way too fast to me, so I am thinking that I
>need to look for a motor putting out 10-20RPM instead. Seem reasonable?
>> > Cutting blade: Nylon blade adapter intended for use on string
>> trimmers.
>> Tried it. Not much success. My current blade is a 7 in circular saw
>> blade.
>Using a metal blade isn't feasible for me. I have small kids. What were
>the principal problems with the nylon blades?
>> I used a radiator fan motor. It has the heft to carry the saw blade,
>> which is
>> smaller and flat. So the saw blade actually spins faster than the
>> original
>> fan blade.
>Any idea of the current draw for the radiator fan motor?
>> > Grass cutting pattern: Random
>> This is actually a real problem. By necessity the cut path is much
>> smaller than
>> Again I haven't gotten this far, but I'm pretty sure I'm going to
>> implement
>> a real grass height detector and cut uncut grass.
>Did you see my earlier post on using an IR LED emitter/detector pair for
>uncut grass detection? I realize there are issues with the
>emitter/detector getting blocked by dirt or cut grass, but does this idea
>seem feasible?
>> a completely bounded area and bump sensors. Somthing like the very
>> popular
>> railroad ties. Anything I wish to protect will be bounded also.
>Eminently reasonable. I also have been thinking along the lines of
>keeping it simple for the initial implementation just so I can get
>SOMETHING working, rather than never finishing anything due to an overy
>complex design.
>> Also I'm an advocate of dropping core knowledge here. Many of us a
>> software
>> or firmware folks. However trying to figure out how to attach an
>> axel to
>> the driveshaft of a motor is a completly different skillset. I'd
>> like to
>Speaking of which, how did you attach axles to the power window motors?
>The specs on the ones I have been looking at say that the output shaft is
>only 5/8 of an inch long.
>Thanks for the informative post,
>Adam Bryant (age 0x23)
>abryant nospam at (work)
>adamdb nospam at (home)
>Parker, CO, USA
>Robotics, RC Airplanes, anything using a PIC
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