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Bird & Tom great take re: position & draft control Just a few things Tom mentioned that I should have touched on. Toms dead on right, the term constant depth is used rather loosely especially by mfgs. They would like to make you think of it as auotmatic sense both up and down & that the slightest deviation in implement angle/hieght change would cause exact output to compensate. this is not 100% the case there is a bit more to it than that. while they are not totaly wrong the device can and does work but like all things there is some limitations. Toms right about lowering to a certain point & if the 3ph needs to go lower because of a out of range condition-(beyond physical ability of the travel limits and the limits of the mechanicle sensing device. But hey it's not a perfect world nor are we or our machines. another thing tom pointed out is he mentioned soil conditions or hard objects, he is right about that a good portion of draft sence is based on that objective... lifting the hitch to a point where wheels grab more as the implement is lifted. I supose my previous post wasn't to indicate its a full featured automatic closed loop control, it does have a few traits of a open control loop the more I think about it there is a base setting as mentioned regarding selecting the proper ratio of the center link. Positiong the top middle or bottom hole for the top link. This not only dials in the varing geometry to the imlement/tractor relationship but it also trims out or amplifies the varying sensing signal for the mechanical to hydrolic relationship a s.p.f.b (set point feed back) if you will. simply stated hit or dig into a hard object or as implement digs in due to geomety change from irregular surface contors than there will be a compensating out put proportional to the input signal. But then goes back to a certain point because of gravity on the implement.

So what I think it all comes down to is some mfgs publications hit more on continuos depth control. Vrs: hieght of varying terain, & should point out a bit more of what tom had said reguarding load change, force aplied to implement and depth contol. But in real world there are both factors to be considered, force on implement and geometry of implement sensed back to draft control. Both are a function of one another. Because if the implement is engaged with the ground either one of these variables- hieght/angle of implement or force applied to implement will cause an output to 3ph. So if we want a dead on accurate depth regardless of any condition I think it would be god awfully expensive to employ on a compact tractor. Maybe on a ultra slick grader but not a 10 to $30,000 compact tractor. Not to mention the tractor would most likely need to move much slower to keep pace with what is going on in back of the machine and stay at a
consistent depth. so now that I have looked at this
feature and thought about it more I have suddenly gained a great respect for this rather simple looking device, although not simple once you consider all the components to actually perform draft control ie: sensing spring, linkage rods, cam plates,and extra hydrolic interface on the rock shaft. Ajustments looks like living nightmare to set up without shop manual at hand.

Please more input on this if I have missed something. Great
board topic I usually don't write in, only read posts.
I find it interesting and always learning from different topics.

What is Position Control
Operating and Attachments
Replies 15 Post by Rob in Mass