Society of Robots - Robot Forum
Mechanics and Construction => Mechanics and Construction => Topic started by: alphaCentaur on January 21, 2014, 08:19:03 AM
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Hi everyone !
This is my first post here and I would appreciate your help.
I am trying to find suitable motors for a four wheeled robot and doing the following calculations:-
Robot Characteristics
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weight(w)=50 kg
wheel diameter(d)=8 inch=0.2032 m ==> wheel radius (r) = 0.1016 m
required velocity (v) = 1 m/s
required acceleration (a) = 0.1 m/s^2
inline angle=0 deg
no of wheels = 4
expected efficiency = 0.85 ( 85 % )
Calculations
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required force (F) = m x a = 5 N
required Torque (T) = F x r = 0.508 Nm
required Torque per wheel (Tw) = T/4 = 0.127 Nm
required torque for 0.85 efficiency Tw=0.149 Nm ==> Tw_kgf= 0.0152 kgf-m
required rpm = (V*60)/(pi*D) = 93.989 rpm ==> rps= 1.567 rps
RMF = Torque * rps = Tw_kgf * rps = 0.0239
However, the RMF calculator shows an RMF of 0.768 kg*m*rps. (screen shot attached)
What am I doing wrong here ?
Thanks.
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Note that the RMF calculated is for a single motor, and you divide the values in four for four separate driving wheels.
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@jwatte
thanks for the reply, but still there is a large difference between values:-
RMF (from RMF Tool)/4=0.192
RMF (from manual calculations)/4 = 0.005
there seems to be something wrong with my calculations maybe, but I am unable to trace it.
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You already divided by four once, so the second calculation of RMF should not be divided by four again.
Separately, it seems you are approximately a factor 10 off, which to me means you may be missing or double-counting a N to kgf conversion factor.