Need help with gear ratios

[crusher]

Hi, I am cutting gears for a scratch built excavator and cannot seem to wrap this old brain around gear rations. I have a motor that turns 15rpm, I have a driven gear with 44 teeth Dp12 I need to know what dimensions the drive gear should be (15rpm). This is for the swing on the house.
Any help would be appreciated.
Terry.

[Lil Giants]

What's the diameter of the 44 tooth gear?

Pictures of parts would help too ;)

[crusher]

Thanks for the reply, I guess what I really need to know is what would the 1/14 scale rpm of the swing be on a cat 320b, from that I can work out the gears needed.
Thanks
Terry

[Lil Giants]

I got one hoe a part at the moment, I'll count out the teeth & measure diameters of crown & pinion to post tonite... you can fine tune the speed via esc EPA's to your own comfort level.

[crusher]

Thank you, that would be a big help. This my first build so am learning slowly.
Terry

[Lil Giants]

crown gear: 70 tooth 107mm dia
pinion gear: 12 tooth 20mm dia
12v motor w/264:1 planetary gearhead running 40rpm on 3s lipo

I manipulate the speed with dual rates radio programming, I have a slow speed for up to 90 degree swing with precise control for minute movement & a higher speed for 180 - 270 swinging - fast digging.

I have a pic, but photo host not seemingly working atm (not for me anyway), maybe it will show tomorrow...

http://img.photobucket.com/albums/v150/protrker/Jan%2016/003_zpseexabws0.jpg

[crusher]

Thanks very much for taking the time to send the info, just what I need to carry on.
I have cut a 12 tooth gear and will tackle the other tomorrow, I also ordered a motor today.
Much appreciated
Terry

[Rimrock]

Just a couple of comments here; the rpm of the excavator swing of the 1:1 version and any scale model of it, will be equal. Joe's machine turns about 6-7 rpm, which is normal for a 50 ton + digger. Smaller machines like 320 do turn a bit quicker, say 10 rpm. Concerning gear sizes, one usually would start out determining the size of the final gear, the biggest, placed in the slewing ring, and then work one's way back and find a suitable gearmotor. The layout and design of your slewing ring will decide how big gear one can place there. 'Larger is better' one can say about the final gear placed in the slewing ring, as a bigger gear here reduce the strain of the tiny gears in the gearmotor.
If one got a 15 rpm gearmotor, then the final ratio will be 15rpm/10rpm slewing ring speed = 1.5 If the largest gear is 44 teeth, then the driven gear would be about 30 teeth (44/30 = 1.47 , 15 rpm / 1.47 = 10.2 rpm)

[crusher]

Thank you for your reply Rimrock, the ratio thing is slowly sinking into this old head.
Terry