The task (lawn mower topic)

[Tommy_T]

The task

Automatically mow a field 100ft x 1000ft.

Task started: 4/2018
Task Completed:


The tool.


I found the mowing deck on Craig's list 3 months ago,
the engine was blown so the mower deck only cost me
$300, then I found an 14.5hp Briggs engine on Craig's
list for $120 and with a little searching I also found an
electric PTO clutch that fit the engine for $60.


the next thing I need to find is a 24Vdc alternator. the briggs engine has
a 9 Amp 12vdc alternator to charge the battery for the 12vdc system(PTO clutch, Arduino(2), Lights, PC and starting engine).
The Electric drive system is 24vdc.

Electric Drive System:
(1) Sabertooth 2x60 with the V2(kangaroo) motion control board.(Serial interface)
(2) 1000 watt electric wheelchair motors with encoders.($150 from Ebay, sweet!)

Control System( Manual Mode ):
(1) Arduino Mega
(1) Arduino Nano (Safety System)
(2) XBee-PRO 900HP

Control System ( Automatic ):
(1) Lanovo S10 laptop PC (Windows XP)
(1) US Digital USB4 device(I/Os, encoder cards, analogs)

Current Senors:
(1) Yocto-GPS
(1) Yocto-D3
(2) Encoders (odometer, Direction)



Tommy

[jwatte]

Looks like a fun, real-world system!
How much fabrication experience do you have? Do you have machining tools?
I'd love to see more about how this project goes!

[tician]

Looks like a fun, real-world system!
How much fabrication experience do you have? Do you have machining tools?
I'd love to see more about how this project goes!

This is Tommy_T we're talking about, jwatte. It's another developmental stage of the Magnificent Mule; autonomous instead of human control through FPV or direct viewing from the porch.


Not sure I would trust any of my code to safely on a platform equipped with a proper gas-powered mower deck. I would definitely have to build a collision sensor system around the bot's perimeter to ensure nothing ever gets near the blades.

[Tommy_T]

It's another developmental stage of the Magnificent Mule

tician, I see it as too big a task for the mule. the mule is just not fast enough.

this platform is designed for mowing speeds needed to do 3 acres in 6 hours.
and with the gas engine also strong enough to charge the battery packs they can
be greatly reduced in size and weight.

this platform is also using servo motors for it's drive system.

the Mule System is waiting for snow.



Tommy

[Tommy_T]

It can't be said I didn't give an electric mowing deck a try.



but, after seeing what a 14hp gas engine can do with even very overgrown
grass like the below image, I'm sold.



Tommy

[Tommy_T]

Not sure I would trust any of my code to safely on a platform equipped with a proper gas-powered mower deck.

tician, this platform while using a different control protocol(serial), does use the same safety logic
as the mule, which has demonstrated its worth countless times.

It turns out these gas engines have a terminal on the coil of the ignition system that when ground is
applied it stops the engine, so interfacing the engine kill to the control circuits is very straight forwards.
also, the mower blades are controlled by an electric clutch, which is also easy to connect to the safety system.

the electric clutch draw 5amps at 12vdc.
the gas engine has a 9amp built-in generator.


Tommy

[Tommy_T]

Plan A:



record a perfect sequence of going 100ft then turning 180deg to the left with a .5 ft overlap of
last cut path, then going back 100ft and turning 180deg right with the overlap, then stop.



take an image with a webcam of a target area. using that image I should be able to correct any
alignment issues from last cut path, then just rerun the last recorded path.

the high contrast between sky and tree tops should come in handy.

repeat 154 times.

the pauses should come in handy as a way to control drive motor temperatures.
it does get very hot out in the sun.


Tommy

[jwatte]

Because it's a known, surveyable area, you totally should use RTK GPS. You can get centimeter precision using just that!
Adding vision and other sensors would be candy on top.

Also, 14.5 HP is just, what, 11 kW? How much safety do you REALLY need for that anyway? :-D :-D

Using LiFePo4 batteries as stabilizers for the alternator seems like a great idea, as long as you can avoid overcharging, presumably by shunting in some big resistive load of some sort (or turn off the alternator.)

[Tommy_T]

Because it's a known, surveyable area, you totally should use RTK GPS. You can get centimeter precision using just that!

jwatte, I'm sure it would help, but not sure how it would handle tree lines the block sections of the sky(lost satellites) errors.

I'm looking into it, thanks.

Tommy

[Tommy_T]

Just as I was about to test the record/playback software one of my motors failed,
seems like a motor brush problem(spring broken).



Tommy