Motor Selection

[Heavy Metal]

Looking for some opinions on motor selection for 1:14 scale JD 710J hoe/loader. I have a couple motors I bought 2 years ago. At the time I did research extensively on the old GT board and German forums as well as doing some torque and speed calculations on paper. I was going for slow and powerful. In the end I selected and purchased two matching gearhead motors, one each to drive the rear wheels (unlike the real thing this will be 2WD). I didn't save any of this old research and don't remember specifics as to why I selected these so would appreciate some opinions from those w/ experience building 1:12 to 1:16 loaders and dozers. Goal is to have power to push the loader bucket into a pile of loose dirt but also be able to move about at reasonable speed. Use assumption that model is heavy as possible and tires are grippy rubber approx 4 1/4" (108mm) diameter.

Motors I have are 12v 200:1 gearhead from Anaheim Automation. Motor is 5000 RPM and geared down will turn 25 RPM. Torque is rated 65 in-oz continuous and peak 250 oz-in. Model: BDSG-37-30-12V-5000-R200. Here is link to web page w/ spec table:
http://anaheimautomation.com/products/brush/dc-gearmotor-item.php?sID=258&serID=3&pt=i&tID=102&cID=46

Do you guys think these will do the job in terms of power and correct top speed? Do you have links to other motors that you would personally have selected for this particular application?

I should also note that, for various reasons, including need for space and alignment I am thinking of mounting the motors to two same-size spur gears before transferring power to drive axles. I could then swap out gears and adjust the drive ratio up and down.

Here's what I'm looking build:
http://i306.photobucket.com/albums/nn265/jbothell/NV192079_0.jpg

Regards,

Joe

[Espeefan]

25 RPM sounds like it's in the right ball park for speed and power. What you need to do is figure out your tire diameter, and then run the math to figure out it's actual MPH, at full speed, or the feet per second of travel. Just figure out your tire diameter, figure out the circumferance, and multiply the distance traveled per hub or gearhead motor revolution. That will let you know how fast the model will be.

[Heavy Metal]

I did the math again and motors I selected would do 27' per minute (.45 FPS or .31 MPH) assuming my target tire diameter of 4.14". That's pretty darn slow for moving from one job to next! I obviously selected these motors for the power.

If I stick with these I definitely need to think about way to adjust ratio. I can't mount them directly to the axle anyway because I miscalculated available space for two motors back to back...the model would need to be 1:12 for both motors to fit between the rims like that (and since I want to haul it w/ 1:14 truck...I'm sticking w/ 1:14)! So offset mount w/ spur gears driving axles would be my thought...then could change gears later if I want to go up or down.

Joe