Near Intersection of I-35 & I-90 Southern Mn. | When I worked as a Tech several years ago now I worked with the Rawson systems somewhat. From my limited experience and fading memory, I believe the Rawson system worked with the stepper motor as follows:
The object like any hydraulic planter drive is to control the oil flow so that the orbit motor turning the seed shaft turns at the appropriate speed to dispense the correct population. The "correct" orbit motor RPM is dependent on several factors such as desired population, row spacing, ground speed, seeds per revolution etc. Both the PWM type systems with a hydraulic drive module and the Rawson style do this calculation.
With a PWM type system, the seed shaft has a shaft sensor on it that reports back to the hydraulic module the current RPM of the seed shaft. The system compares this to what it believes it should be under the current conditions of desired population, row spacing, ground speed etc. If it find a discrepancy, it changes the Pulse Width of the signal going to the hydraulic valve which in turn changes the hydraulic flow and the speed of the orbit motor. If the shaft speed is in close agreement with the calculated speed, the system continues with the current pulse width.
My observation which could be completely off base is that the Rawson arrangement accomplishes this in a different way. The Rawson system calculates the desired seed shaft RPM also. It controls a stepper motor in the Rawson hydraulic valve. This stepper motor turns at the calculated speed that should result in the desired population. I think of the stepper motor as a "pace car" of sorts. The Rawson drive has a clever mechanical arrangement internally that senses the output shaft RPM. If the output shaft is turning slower than the pace stepper motor, this clever linkage opens up the hydraulic valve slightly more. This increases the oil flow and ultimately the seed shaft speed. Once the output shaft and the stepper pace motor agree, the oil flow is correct. The oil flow to the orbit motor is changed as necessary to keep the seed output shaft turning the same speed as the pace stepper motor.
This pace motor setup was originally controlled by a Rawson control box. The operator had the ability to change the population on the go with the Rawson control box. The Ag Leader stepper control module replaced the Rawson control box and allowed this to be done within the Ag Leader module instead. This had the advantage of using a map based Rx to automatically change the population in different zones. It also produced various maps concerning the population.
You ask why the system has apparently died and is going away. My guess is that although I believe it worked fine when controlled by Rawson electronics and later with the Ag Leader stepper module, it turned out to be unnecessary when other systems became available.
My understanding is that Trimble purchased them and then dropped the product line.
As far as repurposing the Ag Leader module for other uses, I think it should be possible but may not be worth the effort. I believe one limitation might be that the output to the stepper motor is likely quite weak since the stepper motor in the Rawson valve probably doesn't need to do much "work" since it just sets the pace. A more powerful stepper motor could likely be driven with some type of motor driver.
I think a major stumbling block would be to work around the programming built into the module which calculates the speed of the pace stepper motor for a planting situation. These calculations would likely not be applicable to other situations.
You ask about running something dealing with cover crops where they are dispensed by a stepper motor. My first thought would be that the circuitry may not be "heavy duty" enough to run an appropriate stepper motor. A motor driver device should be possible though. By doing some mathematical calculations or "trial & error" it might be possible to lie about some of the settings to make the desired application rate correct. Now that I think about this, I believe the Rawson might have some other sensor type circuitry that could be a problem A wiring diagram would be most helpful.
This may be one of those "Solution looking for a problem" situations.
Edited by tedbear 12/19/2025 01:52
|
Other uses for an Ag Leader Stepper seed control module 4001385
