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| If you are going to run any number of motors in series, there are not many choices for a motor that is tight enough internally and has the correct valving to achieve the results that you desire. One motor that will work is the Ross MG series or the Parker TB series which is the new designation. These motors use a 'zero leakage' commutation and will run very consistently at wide range of speeds and pressures. The other choice would be a Char-Lynn T series motor with low speed valve option. The later motor is not readily available as they are special order with the low speed valve. The Parker-Ross is readily available from any number of sources. Always use the biggest displacement motor possible as it will make metering easier, pressure lower and rotation smoother. If you were direct driving your seed meter assuming a 30 cell disk, The motor would need to turn @24 rpm at 5 mph to achieve 30,000 population. If you used a 12 cubic inch motor that would be 288 cubic inches/minute or only 1.24 gpm. That is a pretty low flow to meter and virtually inconsequential in regard to tractor hydraulic load. If you use the drive shaft and have say a 1.5 reduction, that sill would only be 1.87 gpm. Remember that when you run the motors in series, a new motor will need @ 150-200 psi just to overcome internal friction. If the motors are 'broken in' with some form of run-in under high load this pressure can be brought under 100psi with no loss of volumetric efficiency. The small Char-Lynn 'J' series motor is a lousy performer at low speeds. I will never know why Rawson or anyone else uses it for a drive that requires high volumetric efficiency at low speeds. It's ok for speeds over 400 rpm but below it is extremely 'loose' and must drive the pmw loop nuts. Check out the 'Veris Drive' made in Salina KS. It uses a Nichols 110 series motor of relatively high displacement. The Nichols is a pretty good motor, but still won't match the Parker,Ross motors mentioned earlier. Remember that shaft speed commutated motors are usually built with a certain amount of valving overlap which is fine for speeds above 200 rpm but create volumetric efficiency problems at low speeds as the timing elements can leak across ports and cause the motors orbital section to run slower than it's theoretical displacement allows. I realize this sounds strange but if you have any more questions, I would be glad to elaborate. | |
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Hydraulic Drives to control Planter sections
