Am building an unmanned ground vehicle.its a 4 wheel bot.I want to use one motor for each wheel an need help in calculating the torque required by each motor so the bot can move at a max speed of 5mph.the total weight of bot is 60kg.no gears are used and the motors directly connected to wheels.the diameter of each wheel is 10".

What angle of incline do you want the bot to be able to climb?

A max inclination of 15 degree.it basically has to maneuver its self through an obstacle course.I was thinking of using 3hp 13.4Nm torque motorsbut am not sue with it

That should be plenty. In fact, perhaps too much. The total force you need to apply to the wheels is:

Force = Weight*sin(15)= 60Kg*9.8 m/s^2*sin(15) = 152 N.

The resulting torque to apply to the wheels is:

Torque = F* 5in = 152 N* 5 in * 0.0025 m/in = 1.9 N-m

So if you have 4 motors each need to apply about 0.5 N-m of torque to get the bot up the incline. Now, you need a bit more than that to allow the bot to accelerate, and to overcome resistances in the gear train and friction of the tire on the ground, but of you have four motors each with 13 N-m torque you have really over-sized them.

In terms of horsepower:

HP = Force * velocity = 152 N * 0.22 lb/N * 5 miles/hr * 1.47 ft/sec per MPH = 250 lb-ft/s, or 0.45 HP.

To put this in perespective - remember that a 1/2 HP motor is more than enough to run an overhead garage door opener - so if you are thinking of four 3 HP motors your bot will probably hit 60 MPH in a few seconds! One motor will be more than enough.

Thanks a ton for your help.I guess u have made a small mistake in the equation

The resulting torque to apply to the wheels is:

Torque = F* 5in = 152 N* 5 in * 0.0025 m/in = 1.9 N-m

shouldn't it be F=152N*5in*.025m/in=19 N-m.since 1inch=.025m.

shouldn't it be F=152N*5in*.025m/in=19 N-m.since 1inch=.025m.

Yes - you're right - good catch.

Thanks a lot dude.I guess that will help me select the motors.hope I can stay in touch with you through Facebook.

ebaines... dude I have some doubts regarding that calcutation when you take 152N in hp calculation is 0.45 hp obtained hp of each motor or total hp

Dude - that's 0.45 total HP, given that you want the bot to go up a 15 degree ramp at 5 MPH. Divide by 4 to see what you need at each wheel. Same with the 19 Nm of torque that you need.

Oh OK... so if each motor is .11 hp and correspondin torque is 4.7Nm... dont you think it's a lot torque for a .11 hp motor... and how to I calculate the appropriate rpm for this

1. Pick a motor to use.
2. Check the specs for that motor to find its recommended RPM range.
3. Calculate the gear ratio that will drive the wheels at your expected speed (5 MPH) that matches the "sweet spot" of the motor operation.

The relationship between torque and HP is dependent on the RPM of the motor:

HP = Torque (lb-ft) * RPM /5252,
or
HP = Torque (Nm) * RPM /7097

Note that if the RPM is relatively low, you need a motor with more torque to get the HP you need. Given that you have 5" radius wheels and want to go at 5 MPH, that means your RPM of the wheels is only 168 RPM, and the HP needed is:

HP = 19 Nm * 168 RPM /7097 = 0.45 HP

If you went with smaller radius wheels you could use a motor with less torque and get the same acceleration.

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Hii could people please suggest me on how much torque is needed to rotate a wheel bearing 1 kg wt over it please any help would gladly be accepted contact me on [email protected]

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