# Servo-motor with linear interpolation?

#### poklop

##### New member
Hi, the servo motor with linear interpolation, writting by table, doesn`t works as linear, but its work like spline.

How can you to create a linear move? Especially writed by table of magnitude of possition?

#### huliyar

##### New member
i did try to use the table with 'linear interpolation' option. but it still works like the spline interpolation, though the graph shows the table as linear.

you may have to try the 'user defined' instead of table to get a linear interpolation.

#### Os2man4

##### New member
I've run into the same problem and have been unable to figure it out either.

Its frustrating, but I have worked around it by using the table.
I just wish I knew what was going wrong with the linear interpolation.

#### poklop

##### New member
Thanks HULIYAR, I`ll try to fix that problem by using a "user defined" but I still don`t know how to create FORMULA with borders from "a" to "b"

for example: y=3*x but I wont to create line only from 0 to 2 on the x-axis

Can you Help me?

I appriciate you help Hulyiar

#### huliyar

##### New member
hi,

i tried to get the linear interpolations using the 'user defined' option. what actually should be simple enough to do using the 'table' option, is very hard with 'user defined' function using expressions. however, i did try and got this thing to work. we need to do some manual calculations before entering the data. for example, i made a rotary joint, which needs to rotate one full circle at varying speeds. Say 0 to 90 degree in 5secs, 90-270 deg in 5 secs and 270-360 deg in 20 secs. for this i should key in the following expressions and domains

Expression Domain

t*18 0<=t<=5

t*36-90 5<t<=10

t*4.5+225 10<t<=30

i am arriving at the expressions based on equation of line (y=mx+c). there should be a more simple approach. if any of one knows, please enlighten us all.

thanks... huliyar

#### poklop

##### New member
Thanks Huliyar!!!
You help me to fix that problem.