robot motor factor - question ???

[ibot]

Hi,

I calculated the robot motor factor using the rmf calculator. Surprisingly I got very huge #  = 589. I guess I am doing something wrong... any help would be greatly appreciated.

Total weight of the Robot = 250 pounds
velocity = 10 mph [seems 14 feet per sec ... may be my calc is wrong ..    ]
***  acceleration = 3 ft/sec^2 [used the default value in the calculator ] .. any help with this piece would be great !!!
no inclination
wheel diameter = 6 inch
2 powered wheels

below is the way I am calculating rmf factor for a servo .. is this correct ?
ex: HS 311 servo,
Torque: 42 ounce-inch & .20 / 60 deg rot [well the 42 ounce-inch Torque probably when there is no load]

RMF for this servo = rps * T = .5 * 42 [o-in] = .5 * .2 [ft-lb] = .1 RMF 

I am pretty sure .. I am doing something wrong .. if my calc are correct .. it seems really heard to find a servo [or 2 servos] to support a 250 pound - 10mph robot .. 

In case if somebody was wondering ... what is this 250 pound thingy .. the parking lot of my office is so big that it takes 10 minutes of walk to get in. and I have to use it 4 times a day. so, 40 minutes .. hmm .. thought nice to have a robot/rc controlled mobile vehicle ..

Greatly appreciate any help !!

Thanks,
Vivek Kosuri.

[waltr]

I am pretty sure .. I am doing something wrong .. if my calc are correct .. it seems really heard to find a servo [or 2 servos] to support a 250 pound - 10mph robot ..  Sad

Your calc's are correct.
Yep. Hobby servos will not move this weight.
Look into Wheelchair motors.

[Cristi_Neagu]

You are talking about a 250lbs vehicle... You don't use servos, you use DC motors. Think golf cars. I think you could use car starter motors, but they might not work too well. Either way, you don't use servos!

[Soeren]

Hi,

In case if somebody was wondering ... what is this 250 pound thingy .. the parking lot of my office is so big that it takes 10 minutes of walk to get in. and I have to use it 4 times a day. so, 40 minutes .. hmm .. thought nice to have a robot/rc controlled mobile vehicle ..

Did you consider an electric "scooter"?
They come in various configurations:

With the blue one, the handlebar can be folded down and it doesn't take all that much space in a trunk.
Not trying to rain on your parade, but I bet that it would be both smaller, lighter, cheaper, faster, more efficient and prettier than what you plan.

2006 Razor Electric Scooter E300 15 MPH
Item# 13113640
Sale: $173.59
http://store.platinumgalleria.com/razor-electric-scooter-e300.html

You could probably get them a lot cheaper if you spend some time shopping around for it, but even at that price, I'd get one immediately, if they weren't extremely illegal in Denmark (the Danish police just upped the chase for Segways, as there seem to be a fair number of them running on public roads).

Here's a link to several of them in different power and price levels (with links to places where you can buy them).

[ibot]

wow !! that scooter is a cool deal .. But, I am wondering what type of motors required for such a scooter ?

it is pretty clear from below messages and calculations, servos cannot handle such a load.. will there be electric motors that can handle these loads?

and what type of power supply might be needed to run such motors ..

Greatly appreciate your help !! Thanks !!

[waltr]

will there be electric motors that can handle these loads?

There are motors that are used for locomotives and commuter trains.
So, yes there are motors available. A few suggestions have been made in above posts.