For a length of line-follower shaft (chassis) has a direct correlation with performance of the bot itself:
Having a longer shaft → faster turns (extremely desirable) best to have >20cm if possible however constraints force 2cm which is 10x more problematic
The PCB Itself acts as chassis material which is a VERY good thing since it allows for a much cleaner design because the ICs and connections are integrated.
Usual Design:
Custom chassis plastic rollers sensor mounting attachment 2 high rpm motors custom motor cover m4 bolts & nuts custom carrier PCB custom line sensor wheels brass spacer
PID-controller guidelines:
Proportional: easy to make & good of way of testing hardware however it overshoots or moves too slowly may make unnecessary zig-zags on a straight line
so in context of line-follower
steer = (A-B)* KP
KP = gain factor A = analog value from a sensor positioned from left of center B = … from right of center
so if A = B ⇒ steer = 0 this implies the bot will move straight
using I & D
steer can be summed as: steer = P + I + D
P = (A-B)*KP I = ([A-B] + I)KI → fixes steady-state errors D = (P - last error)KD → reduces overshoot
last error = A-B
Using Just P → never works Using P with some intersections of the line tape to follow → ehh using proper PID → pretty good then depends on bot structure & motor RPM and wheel diameter etc etc.