Re: [mowbot] Re: Gotta have gas to cut ??

KEN_REED nospam at
Fri, 7 Mar 97 08:30:00 -0700

>Previous Message:
> >>>I believe the disk is important since it would stir the air less
> >>>than some form of a cross. The air would be churned up by a cross
> >>>always pushing air out of the way, and it moving right back in.
> >>>It's interesting you used the phrase "propeller type arrangement",
> >>>since it would be a zero pitch propeller.
> >>>Note: I haven't experimented with anything but a disk, and I'm
> >>>satisfied enough with it that it is designed into my LawnBot.
> >>>To me it seems intuitive that a disk would cause the least air
> >>>friction losses.

OK. Mind telling some specifics?

1) Exactly what kind ot motor. Would something like the heavy duty motor
at Rat Shack be feasible? What about maybe a 12V DC fan motor?

>>>My motors are about 75% the size of an automobile fan motor,
>>>permanent magnet type, with a tach. They have a 1/4" shaft coming
>>>out of either end, and have permanently sealed roller bearings. I
>>>found several at a local surplus house and bought all of them,
>>>(spares you know). They also have a tachometer on them, which
>>>might be nice to detect stall of the mower system.

2) What is the thickness and mounting method for the disk?

>>>For my test I used 0.042" thick aluminum sheet cut out with a hand
>>>held saber saw. I used a crude, but effective method to attach the
>>>motor to the disk. I used the clamp on type electrical connector lug,
>>>the type that have a set screw to tighten down on the wire. They are
>>>available for wires from about 10gauge and bigger. They have a tab on
>>>them that I bolted to my disk. This is not a good arrangement for
>>>permanent mowing. It vibrates quite a lot because its not balanced,
>>>But for the 30 minutes of running that I did for testing, it worked
>>>great, and took about 20 minutes to make one test disk.

>>>For my actual LawnBot, I'm going to turn out some adaptor hubs.
>>>They will have 4 setscrews to attach securely to the motor shaft,
>>>and a hub to bolt on the disk. I'm using 1" diameter aluminum
>>>shaft stock to turn them out of on my lathe. I've used the
>>>same method, but with 2" shaft to attach my drive wheels to the output
>>>shafts of my dc gear motors. I've used this arrangement on many
>>>personal robot projects, up to 150 lbs weight.

>>>(Personal note:
>>> I believe anyone serious about making their own complex robots
>>> should find a good local machine shop that does good work,
>>> and has reasonable rates. Most machine shops aren't
>>> all that high priced. You have noted that Dave Everrett is
>>> doing this. My solution was to buy a "ShopTask" combination
>>> vertical end mill/lathe. Its fine for me, and I use it on the ranch
>>> and for many projects, but then I have a bit of a machinist
>>> background. It cost about $1700. Its interestig to note
>>> however, that most hobbyists would not spend $1700 over several
>>> years of going to a machine shop for their work. One warning,
>>> those with great tools have lots of FRIENDS that they never see
>>> unless the friend needs a part made, or something welded.
>>> ---Okay no more editorial, just the facts Maam. :)

3) Any idea how to handle cutting on an incline? Will the cutting disk
simply always be perpendicular to the body of the Mowbot or does it have
some type of movement relative to the body.

>>>Just like a regular mower. Motor w/blades attached firmly to the