Gear ratios for outrunner motors?

[DeathBlade]

I've been looking at quite a few RC motor builds recently and I'm thinking bitting the bullet and starting one. In most builds I've seen either a huge rear sprocket like 80-150T driven by a 10-16T or double reduction gear boxes like in Bubbas build.

So what is the usual gear ratio more people use on their builds?

I've was on harbor freights web site and saw a small 33:1 planetary gearbox and I got thinking about making some kind of crazed geared hub motor of doom. With one of these. http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=5140&Product_Name=HXT_80-85-A_250Kv_Brushless_Outrunner_(eq:_70-40)

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=93645

If my math is right 250rpm/v = 48v*250 = 12,000rpm / 33 = 363 * 79"(tire dia) = 28,727" / 12 = 2,393' / 88 = 27mph

 

[etard]

That's very compact, my concern would be with the speed that RC motors operate at, I don't think this gearbox will hold up to anything above 3000 rpm.

Other than that, I am going down to the local store to check it out.

 

[dontsendbubbamail]

If you want to go with a planetary gearbox, you should look at what Jason is using. My hxt 80-100 130 kv motor only needed one jack shaft, but I used two because I might go back and play with my 230 kv motor. With the one jack shaft, you could get away with a 52 tooth sprocket on the rear wheel and keep max speed at 27 mph. I suggest you step up to the hxt 80-100 to get more power and the lower kv.

Bubba