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Motor choice for low speed, low torque series application

Motor choice for low speed, low torque series application

(OP)
I am looking at converting my drill (soybean and wheat planter) to hydraulic drives to allow for variable rate and clutching; it is currently ground driven. 30' of drill will be divided into 4 - 7.5' sections, which will be automatically controlled.
System design as follows:
  • Monitor supplies PWM signal for rate control and 12V output for each section control (uses radar and RTK corrected GPS for speed input and application control)
  • Brand EFC proportional valve
  • 5 motors in series:
    • Idler motor constantly running a shaft sensor (360 pulses/rev) - nil torque requirement
    • 4 motors to turn the seed meter shafts, each with a solenoid valve plumbed to bypass to provide clutching for the section - 30 in-lbs of torque on each of these
Target rpm range for the motors is 0-50. Motors will be driving a #40 chain, so negligible shaft load. Looking at around a 15 in/rev displacement to be in a reasonable flow range for the proportional valve. Smooth operation at slow speed and low leakage are very desirable.

Now the question: I'm trying to pick out the best motors for the application. I have been looking mainly at Char-Lynn because of ease of availability. A T series (spool valve, geroler) with the slow speed valving option sounds good,but I don't see that I'd be running the recommended 300 psi difference between A and case pressure - I don't know how critical that is with such a low load. A 2000 series (disc valve, geroler) would be another option - the application charts show lower flows and speeds than the spool valve designs. Does a disc or spool valve tend to handle low speeds better and does one inherently tend to leak less than the other?

Thanks for your time, Casey

RE: Motor choice for low speed, low torque series application

I can't provide an answer but:

1) Generally speaking the disc valve motors are better (smoother) at low speeds than the spool valve motors. However, at such a low torque requirement there may not be too much difference.

2) At such a low pressure, leakage shouldn't be an issue with either motor.

3) The 300 psi minimum pressure requirement is to avoid the possibility of cavitation if the motor overruns (since the low speed valving option uses narrower slots in the spool valve).

4) The 2000 series motor will probably cost you 40 - 50% more than the T series.

RE: Motor choice for low speed, low torque series application

Look at Parker gerotor motor. No valving.

Ted

RE: Motor choice for low speed, low torque series application

(OP)
Thanks so much for the replies; I had been struggling to find any reliable information between the different valve types. The "zero leak" commutator style is very interesting and may very well go that way. Every LSHT motor around the farm is a Char-Lynn; I expected that the different manufacturers used the same designs. Nothing is commercially available to convert the drills, so DIY is my only option. I farm 1200 acres with my dad. Seed costs have grown considerably in the past 5-10 years, which has made it economically viable to move to automated control systems - to adjust population to soil types and clutch rows to prevent overlap and wasting seed. Couple of pics attached. Converted the planter to hydraulic downforce - every row has a weigh pin and cylinder to keep constant down pressure despite changing ground conditions. The map shows the force applied by the cylinders. The gradients across the field are from the change in seed box weight as they empty, the "U"s on the headlands are from the weight of the tractor slightly compacting the soil where we turn. Also installed electric drives on each row, so each population can be varied and clutched independently. Right at $20,000 all said and done for both. From someone that gets oily, thanks for what you all do, Casey

RE: Motor choice for low speed, low torque series application

Quote (Casey)

From someone that gets oily, thanks for what you all do, Casey

Hey man.. we get oily too. Some of us. Sometimes.

Seriously though, glad you sorted things out. Few forces are as good at problem solving as a farmer on a deadline.

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