Hi,
I'm working on a small project, where I have a car (just a plate with 4 motors, not the point of the project) and in the centre, I have a stepper motor with a threaded rode, vertically to the ground, and a pen/marker attached to it.
The default position of the motor, is where the rode doesn't touch the ground. (can be also just 0.5cm from the ground, doesn't matter) - but the distance from the ground isn't known, nor fixed. And therefore I can't use a fixed value.
My goal is to make the car draw on the ground - and for that, I need to move the pen up and down. (so it won't be just one solid line)
I'm trying find a way to rotate the motor just enough so the pen will touch the ground - but not smashed into it.
I'm a bit of a newbie when it comes to electronics/mechanics (coming from the programming world) and that's also why I'm doing this project - to challenge myself and learn. ;D
I did some research online, and one of the methods I found, is to use a current sensor. (And then, when I detect an increase of current draw, it means I hit the ground) But it doesn't sound like it is a really accurate way. (nor a good way)
I will really appreciate any help!
Thanks in advance,
Ran
You cannot detect this electrically for a stepper motor. Besides steppers only stall on
large forces, you want to control and limit the force, if the motor has stalled you have already
smashed the pen down hard.
I'd have used a mechanism with a spring to provide the right amount of force, and pull the spring
with the mechanism. A solenoid is a pretty good fit for this application. A spring has compliance
too so it can follow dips and bumps in the surface you are drawing on.
Thanks for explaining!
I talked about it with a friend and he also suggested using a spring, exactly because of that.
However I still have the same problem - to detect when a motor hits the ground. (Or more precisely, an object connected to the motor) - I think that's how I should have asked it.
I thought about several "mechanical structures", using plates and a micro switch, but I'd like to try something more electronic-programming, and to not rely much on mechanical switches, and "external parts" if you know what I mean
I think you will soon discover that a stepper motor turning a threaded rod will not "stall" until it hits the end of the threads. Even if it did stall, there is nothing going to happen to the current pulses trying to rotate the motor.
You will HAVE to consider some other design mechanism to be able to do what you want.
Paul
I would use a small servo and position the pen , but use a spring in the mechanism , to keep it in contact - if you don’t the pens with skip and miss , it needs a light downward pressure ( old biro spring would do it)
