Jerking of robot arm

Dear friends,
I have designed a robotic arm driven by servo motor via a planetary gear box.I have used taper roller bearing & deep groove bearing to hold the driven shaft.The distance between two bearings is 10 mm .When
I turn ON the motor, the motion of arm is jerky.Also, I've used lamina coupling to couple the drive shaft.
The rpm of rotation is very very slow.Some say this may be due to unbalanced load or may be due to less distance between two bearings & improper pre-loading of bearings.
I've also fine tuned the motor.

Please can anyone help me to resolve this problem

Bystander
Homework Helper
Gold Member
planetary gear box.
You might want to "pre-load" the planetary.

Hesch
Gold Member
the motion of arm is jerky.Also, I've used lamina coupling to couple the drive shaft.

1) If the pipes are hollow, fill them up with concrete which is a "dead" material that will prevent swingings. Hollow pipes will ring, ( tubular bells ).

2) Pay attention to the quality of the coupling ( no spring effect ) and lack in the gearbox.

3) You must limit the dA(t)/dt ( A(t) being the acceleration ). This means to control the A(t) by S-curves. Say you are using a digital controller and you have a speed control loop. At the input of this control loop you could insert an array of speed elements. Changing the "soll-wert" ( must-be-value ) of the loop, the array is stepwise filled up with the new speed value. The output of this array block is the mean-value of the elements in the array at all time. The resulting response to a step in the speed function will be something like this:

Following this curve, you will limit shock waves in the mechanical system.

PS: As for 3), I think something is wrong. Anyway I hope you understand the idea.

Last edited:
256bits
Gold Member
There has to be some binding problem arising from misalignment or incorrect tolerances being applied. If the arm is moving in a chattering fashion, it is moving along and experiencing static/dynamic friction as it does so. The slow rpm ( how slow/fast should it be ) could mean the motor has unaccounted torque that it has to deal with.
On paper it may look fine, but upon assembly tightening of components has thrown the paper model out the window.