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Coke-in-MN 
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Joined: 12 Sep 2009
Location: Afton MN
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 Topic: Bobcat A 300 - wheel position
Posted: 14 Jan 2024 at 9:15am |
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Have a A 300 machine with all 4 wheels that will go into steer mode or skid mode .
Machine sort of CRAB Turns with front and rear axles pivoting to allow machine to turn without skidding tires .
Right rear wheel gets a mind of it's own and decides to lock into turning position and stay cocked out of line with other 3 axles .
Had it to Dealer and their idea of fix was throw parts at machine and said it was fixed but a hour of running it here and it's doing the same thing it was brought to them for .
Seems if you wobble stick control and switch between CRAB and Skid switch it will unlock that one wheel but , then go out of kilter again - unexpectedly . Bumping wheel into straight position works for a while - but having another machine to do it against or push it back is not always possible .
Anyone know what the repair might be as Dealers $4,000 fix didn't work for any length of time . Replacing the full onboard computer is something they suggested but cost is a extreme and ridiculous cost . After their last idea " It's Fixed " can't afford their trial and error method .
Edited by Coke-in-MN - 14 Jan 2024 at 11:05pm
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Faith isn't a jump in the dark. It is a walk in the light. Faith is not guessing; it is knowing something.
"Challenges are what make life interesting; overcoming them is what makes life meaningful."
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orangeman
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Posted: 14 Jan 2024 at 1:29pm |
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orangeman
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Posted: 14 Jan 2024 at 1:45pm |
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steve(ill)
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Posted: 14 Jan 2024 at 4:23pm |
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this may be 100% non related.. But Son has a 190 with tracks.. Few years ago it had problems steering on one direction. We worked on the pump, the motor, adjusted linkage, etc..... Hand lever pulls on a cable that ran to a cam/ lever bolted to the valve spool... Found the lever bore was worn a slipping on the spool as it rotated.. Only a few degrees, but enough to cause the problem... Rebuilt the lever bore / bolt clamp for better clamping..
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Like them all, but love the "B"s.
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DiyDave
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Posted: 14 Jan 2024 at 4:47pm |
Sounds to me like it might be a wiring problem. When something gets rubbed or pulled wrong, it acts up. Might also be a solenoid problem, or a hose, too. I long for simpler days and simpler machines... 
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steve(ill)
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Posted: 14 Jan 2024 at 5:11pm |
Seems if you wobble stick control and switch between CRAB and Skid switch it will unlock that one wheel
If not loose linkage, then Daves idea of electrical / solenoid may be an idea.
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Like them all, but love the "B"s.
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Coke-in-MN
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Posted: 14 Jan 2024 at 11:09pm |
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Seems it's all electric wobble stick control - manual switch from crab to skid is located on overhead dash . When moving machine 3 wheels steer fine and all of a sudden right rear gets a mind of it's own - ends up pointing from forward to right direction when other 3 still respond to steering controls
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Faith isn't a jump in the dark. It is a walk in the light. Faith is not guessing; it is knowing something.
"Challenges are what make life interesting; overcoming them is what makes life meaningful."
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im4racin
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Posted: 15 Jan 2024 at 5:55am |
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Sounds like angle sensor for that wheel or the wires associated with it
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jaybmiller
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Posted: 15 Jan 2024 at 10:52am |
1st I'd get my $4K back as it's NOT 'fixed'... 2nd, read manuals and see WHAT actually controls the wheel turning. If all are fed from a 'computer', as others say maybe a 'wiring' issue, either from a sensor or to the actuator that controls the wheel turning. Good news is 3 out of 4 work fine, so process of elimination....
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3 D-14s,A-C forklift, B-112
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DaveKamp
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Posted: 15 Jan 2024 at 11:01am |
So the key element of a Servo system, is the FEEDBACK circuit... the sensor that detects position... because...
IN a SERVO system, the operator's control is read, interpreted, and a command is sent to the servo to "Go to XXXX"... at that point the servo's processing reads the position sensors, compares that to where it WAS LAST, and sends a movement in the direction of the commanded position. It observes the sensors to determine how far it has moved, and how fast.
In a SERVO system, the velocity at which the actuator runs is compared to the DESIRED speed of the command, and if not sufficient, the drive output is ramped UP until the desired SPEED is met, and then, as the target position is approaching, the output is ramped DOWN to prevent overshoot. This all happens very fast.
Since the wheel is going noplace expected, it is likely that either the
sensor is kabashed, or the data going from the MCU to the servo's drive
electronics is messed up.
My GUESS is that they used some sort of Absolue Position Encoder (APE) either a rotary or linear scaled device that has optical incrementations that are unique through it's span, so that it doesn't need to be 'homed' to a startpoint to determine where it ACTUALLY is. Older systems would just use a quadrature encoder, and count from a 'start' point when initialized, to determine position... but in case of an Absolute, when the system powers up, the bits read from the APE identify it's scalar position immediately.
One thing you might note- if the machine powers up, and attempts to swing it's wheels before starting, it's probably a basic quadrature system, and has 'homing' switches.
IF it has homing switches, and those switches gowonky, it will THINK it is 'homed", when it's actually not.
Edited by DaveKamp - 15 Jan 2024 at 11:11am
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SteveM C/IL
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Posted: 23 Jan 2024 at 10:15pm |
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I've said it before....Dave knows everything about EVERYTHING!!!! I can't fathom it!
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