General Misc > Misc

First personal project.

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Tommy:

--- Quote ---A ┬Ácontroller is just a few bucks, but I don't see why one motor would need it while another wouldn't?
--- End quote ---
Soeren
If the main controller(PC) shuts down for what ever reason and the DAC voltages go to 0v with the Sabertooth or RobotQ
Drives will go Full reverse and full CCW turn until the batteries drain, drives fail or the test bed ends up in Cleveland.
With the P&G drive if the main controller shuts down and the DAC voltages drop to 0v the drive will shut down and show
a fault. also if I power up the drives with the main controller(PC) turned off the Sabertooth and RobotQ will take off, but
not the P&G drive, it would show a fault.

It reminds me of the mid 80's when working on the positioning feedback devices on the first generation CNC machines
you always had one hand on the E-Stop button when you first turn it on, because if you made a mistake on the feedback
devise the machine would take off as fast it can until it hit and end of it's ball screw, turning on the test bed with the
sabertooth drive installed and no micro as a hart beat, I hold my breath and have a hand on the E-Stop.

With the P&G drive it's kinda like todays CNCs, if anything is wrong it just faults out.


--- Quote ---Why would it?
Just use encoders on either the wheels or the motor shafts and count pulses, then you know how far each wheel traveled. With a bit of testing, you will probably find how much you need to modify a given distance at a given speed for complete travel.
--- End quote ---
Because I'm not doing random cutting paths(I hope) any deviations from the target path will cause me a problem, with the Sabertooth
and RobotQ drives even if one wheel runs over a toy the kids left laying around or even Dog crap(my mother has a dog) the drive
can make the speed and direction correction very fast(full reverse to full forwards in .5 seconds), because of the Acc/Dec programed
into the P&G drive it takes 6 seconds to go from full reverse to full forwards.

.5 sec = @2.5" linear travel
 6 sec = @30" linear travel
mowing deck on test bed 20", I want it to be 48" when project completed.


--- Quote ---Just use encoders on either the wheels or the motor shafts and count pulses, then you know how far each wheel traveled.
--- End quote ---
because of the reason listed above(dog crap, toys,gopher holes) I can't use the drive wheel in the velocity or positioning loops


--- Quote ---Why would tracks damage the garden more than wheels (as long as you don't rotate too much in one place)?
Tracks will spread the weight over a larger area, so it will be lighter per square area of contact.
--- End quote ---
I was thinking about all that friction while turning, but also how much wider and long they are, and can my mom plant her carrots
without running over the ones she already planted?. I have never used tracks before so my information in very limited.
I willing to give them a try.


Tommy

Soeren:
Hi,


--- Quote from: Tommy on September 02, 2010, 08:17:23 PM ---If the main controller(PC) shuts down for what ever reason and the DAC voltages go to 0v with the Sabertooth or RobotQ
Drives will go Full reverse and full CCW turn until the batteries drain, drives fail or the test bed ends up in Cleveland.
With the P&G drive if the main controller shuts down and the DAC voltages drop to 0v the drive will shut down and show
a fault. also if I power up the drives with the main controller(PC) turned off the Sabertooth and RobotQ will take off, but
not the P&G drive, it would show a fault.

--- End quote ---
OK, plus one to the P&G then.



--- Quote from: Tommy on September 02, 2010, 08:17:23 PM ---Because I'm not doing random cutting paths(I hope) any deviations from the target path will cause me a problem, with the Sabertooth
and RobotQ drives even if one wheel runs over a toy the kids left laying around or even Dog crap(my mother has a dog) the drive
can make the speed and direction correction very fast(full reverse to full forwards in .5 seconds), because of the Acc/Dec programed
into the P&G drive it takes 6 seconds to go from full reverse to full forwards.

.5 sec = @2.5" linear travel
 6 sec = @30" linear travel
mowing deck on test bed 20", I want it to be 48" when project completed.

--- End quote ---
You wouldn't need a full reverse in such cases, just minor adjustments and when mowing the lawn, you won't be going fast anyway, so I'll still recommend encoders (they could be mounted on two springloaded casters for non-slip).



--- Quote from: Tommy on September 02, 2010, 08:17:23 PM ---because of the reason listed above(dog crap, toys,gopher holes) I can't use the drive wheel in the velocity or positioning loops

--- End quote ---
I don't think a turd here and there should upset precision, but that would depend on which sensors you use of course.



--- Quote from: Tommy on September 02, 2010, 08:17:23 PM ---I was thinking about all that friction while turning, but also how much wider and long they are, and can my mom plant her carrots
without running over the ones she already planted?. I have never used tracks before so my information in very limited.
I willing to give them a try.

--- End quote ---
As long as you make all of it yourself, you decide how wide they're gonna be and of which material.
However, I don't think tracks will be a necessity - most people that makes autonomous lawn motors use regular wheels and if the winter means too much slippage, a set of modified (shortened) car chains should help. With cybernetics, neither snow, ice or gigantic turds should be a problem, as it is part of the autonomy to negotiate such obstacles.

If you can post sharp photos of the control electronics and what else materials (schematics, descriptions, links etc.) you may have, we could perhaps find a way to disable the acceleration/deceleration profiles.

Perhaps you should take a look at the CMU cam for navigation purposes.

Tommy:

--- Quote ---You wouldn't need a full reverse in such cases, just minor adjustments and when mowing the lawn
--- End quote ---
Soeren
While on blacktopped pavement your above statement is correct, both drives can do a very good job because only small
corrections are needed, but not on my lawn with it's tree roots, 25deg slopes and uneven surfaces. the P&G with it's Acc/Dec
can't even make it one pass while the Sabertooth can. as it turns out not even the 25Amp sabertooth is up to the task.
The 150Amp RobotQ(don't have yet) should do the trick.


--- Quote ---so I'll still recommend encoders
--- End quote ---
I do have two encoders for closed loop control 1-positioning, 1-Directional velocity, no feedback on the drive wheels(yet)
the RobotQ does have 2 encoder inputs for wheel encoders.


--- Quote ---As long as you make all of it yourself, you decide how wide they're gonna be and of which material.
--- End quote ---
If I was going to add tracks chances are they would be  http://www.snowblowersdirect.com/Ariens-72600500/p829.html?utm_source=froogle&utm_medium=shop+portals

Tommy

blackbeard:
nice idea but it seems a bit under engineered. first off from your diagram it shows casters. casters are a death trap on grass and dirt. now think about this. is it worth spending 2500 on a robot that you have to remote control to cut grass when you can get a riding mower for 1000? also why would you have a wheelbarrow sort of thing if you don't have anything to fill it with? i mean if you have to fill it then it's a little superfluous. lastly i think you could do that with half the budget if not much, much less depending on what you've already spent. a wheel chair is a good platform but you should really think about how to utilize as much as possible and you should realize that they are NOT for driving in the dirt. in fact you will need to change the wheels to something bigger if you intend to use it at all.

Tommy:

--- Quote ---nice idea but it seems a bit under engineered.
--- End quote ---
blackbeard
I'd have a hard time arguing that point, truth be told this is my first project of this type
and with no prior experience I'm learning as I go, for me learning new things comes easiest
when working on an application. I picked the project to help my mother maintain her independence
in small ways around the yard/garden, and for me to have some fun making it work.


--- Quote ---first off from your diagram it shows casters. casters are a death trap on grass and dirt.
--- End quote ---
While the casters are working even on my sad excuse for a lawn they do create uneven forces causing
automatic control issues, the new test bed I picked up has four casters (2 in front, 2 in back) and they
are wider, worst case would be to have to pull the motors from one test bed and mount on the the second
one for 4 wheel drive.

 
--- Quote ---is it worth spending 2500 on a robot that you have to remote control to cut grass when you can get a riding mower for 1000?
--- End quote ---
With what I have now, I could use WiFi to network the testbed's PC with my mom's PC in her living room
and she could mow or clear the snow from her drive and walkways by cameras. I'd pay much more to give
her that kind of independence.


--- Quote ---also why would you have a wheelbarrow sort of thing if you don't have anything to fill it with?
--- End quote ---
The payload dump box is so she can haul potting soil and other things around her yard, she may not be able
to Handel a wheelbarrow by herself anymore but she can use a joystick to move things around her yard and garden.


--- Quote ---lastly i think you could do that with half the budget if not much
--- End quote ---
Right now I have about 1300.00 into the project, my lover could tell you to the penny, but she's not here now.
The big ticket items still needed are the 48" mowing deck, I have a 20" for testing, and the tracking system for
autonomous functions, I'm leaning towards multiple wireless dog fence transmitters, they advertise real time range
information. even if they have values that could change over time due to sun spots or god only knows what, I
could have a master unit in a fixed location to use as an offset for the rest of the units.

 
--- Quote ---in fact you will need to change the wheels to something bigger if you intend to use it at all.
--- End quote ---
The new testbed I picked up has knobby tires, but if need be I would add tracks.

Tommy

  

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