Need help figuring speed

[binfordw]

Hi all,

I have a question. I need to figure out what sprockets to use to achieve a set speed on a project.

Heres the basic info,

2750 rpm motor
10" drive wheels
target speed, 7-10 mph.

I cant seem to figure out what the drive axle rpm needs to be to achieve those speeds. (FPM/pi*dia)?? I came up with 280 rpm at axle to get 10mph.. Is that right?

Thanks in advance

Ben W

 

[ccw]

Hi binfordw,

Here is what I get:

Tangential speed = 10mph x 88fps/60mph x 12in/ft
= 176ips.;

Rotational speed = 176ips / 2PI(5 in.)/rev. = 5.6rps.;

RPM = 5.6rps x 60sec/min = 336.14rpm..

 

[haggis]

binfordw

Your fpm/pi*dia(ft) is right but 337 rpm is the answer as ccw pointed out. This gives you a total ratio of 8.17:1 for speed reduction. Assuming that this drive is roller chain and sprockets, the largest sprocket you could use on the drive axle would have to be around 8” O.D. as the wheels are 10”. So, you couldn’t get a driver sprocket to achieve the required ratio. A solution to this could be (2) 4:1 reductions. For example, if you could get a driver as small as 2” O.D, then an 8” and 2” on an idler shaft and finally, an 8” on the driven axle. Or could you use another motor, say 1750 rpm or 1200 to get the ratio down?

 

[binfordw]

Thanks guys, not sure where I went wrong with the math. Looks like I'll be using a jack-shaft after all.

This site is great, thanks for all the help

Ben W