Mechanics and Construction > Mechanics and Construction

Choosing the right motor

**Kars**:

Hi there

I want to build a robot, and for that robot i need motors. I don't want servos, they aren't fast enough (they are about 60rpm)

I need +- 3kg-cm torque, and about 300 RPM. I've been searching for some motors and i found this one

They look ideal to me, but when i look at the specifications in the pdf file tehy say that the 'Kt' is 130Mn-M/A and the 'Kv' is 71rpm/v

What is 'Kt' and "Kv'?

Did i choose the right motor?

Do u guys have some alternatives for motors?

Thanks in advance,

Kars

**Admin**:

check this tutorial out:

http://www.societyofrobots.com/mechanics_dynamics.shtml

It will tell you if your motor can do what you want.

So robot speed isnt only a function of motor rpm, but also a function of wheel diameter. Servos are really strong and slow. Use a wheel twice as big, and your robot will move twice as fast.

--- Quote ---'Kt' is 130Mn-M/A and the 'Kv' is 71rpm/v

What is 'Kt' and "Kv'?

--- End quote ---

Kv says that for every volt you give to the motor, it will go about ~71rpm faster. So if you give it 6V, it will go about 426rpm - waaaay to fast for most robots! You probably dont want more than 100-300rpm, depending on many different factors.

Im not sure what Kt is, but Im guessing Mn is millinewtons, and A is current. M might be meters. (check the datasheet, it should say!)

So if my guess is right, then it is .13 Nm/A, meaning your motor will apply .13Nm of torque for every amp of current.

**Ro-Bot-X**:

How do you transform N*m in kg*cm?

**Admin**:

--- Quote ---How do you transform N*m in kg*cm?

--- End quote ---

ehhhhh kg is mass, while N is a force . . . :P

if you multiply mass by gravity, you can get a force.

**Ro-Bot-X**:

Ok, Torque is a force right? Then is corect to say the motor has a max torque of say 15mN-m. But how is that converted to kg-cm or oz-in? Just by multiplying it by gravity (9.81m/s^2)? And of course multiplying by 100 to account for meters to centimeters transformation...

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