It looked like the reduction that plowboy was using was a 13 tooth sprocket on the motor and a 36 tooth sprocket on the shaft that drives the meter. I suppose you would call that something like a 2.77 reduction.

I would like to attempt to follow your math on here for the required RPM of the motor on a 30 cell corn disk, 30" spacing dropping 15,000 (slightly lower than I could imagine forcing myself to come down to) at 2.5 mph (say you find yourself slowing down for a rough spot in the field)

On 30" rows, one row would have to go 17,424 feet to plant one acre.

If I wanted to drop 15,000 population, I would have a seed placed every 13.94 inches.

To drop 30 seeds I would have to travel 418.176 inches.

At 2.5 mph (2640 inches per minute) I would have to travel .1585 minutes to drop 30 seeds.

In other words at the lowest population and speed I can imagine, the shaft would have to be turning at 6.313 revolutions per minute.

If the motor turns 2.77 times for every time the shaft turns, the motor will be turning at 17.49 revolutions per minute.

Now let's say I want to flow a minimum of 2.5 GPM so that I may have some degree of control. There are 231 cubic inches in a gallon so I want to use 577.5 cubic inches in a minute. If I divide that by 17.49 revolutions per minute I find that I would want a 33 cubic inch motor if I did not want to involve some sort of a jackshaft.

Now lets go up to 6 mph at 31500 (the fastest speed and highest corn population I could imagine wanting to use). Using the same calculation process it looks like I'd have to pump 12.6 GPM to run that population.

On rare occasions we plant soybeans on our irrigated stuff (maybe once every 5 years). I have never been involved in planting them so I don't know what the disk looks like, but I doubt you could put enough holes in the disk to keep from having to spin it quite a bit faster than what would be required for 31,500 population corn. If it goes much higher than the 12.6 GPM that I had figured, it would become burdensome to the hydrualic system of the tractor because of all the other high volume loads that we would plan on having on the planter we're considering building.

What kind of flow can you accurately meter? Can I go down to 1.5 gallons per minute and still accurately meter the flow? That would change things considerably. Thanks for all your imput.