# Forum: µC & Digital Electronics Back EMF Problem Stepper Motor / Line Follower Robot

Rate this post
 • ▲ useful ▼ not useful
Hello all,

I have built a line follower robot with stepper motors to drive the
wheels. It is controlled with TMC stepper motor drivers from the 3D
printing area and a Teensy / Arduino microcontroller. It is powered by
an 18 volt drill battery.

As far as everything works wonderfully, however, I have now encountered
the following problem:
If I move or drive the car by hand when it is switched off, the stepper
motors behave like a generator, i.e. various LEDs of the circuit start
to light up.

I am therefore concerned that this can damage the controller, drivers or
battery due to this reverse current if you move the trolley too fast.

So now the question:

What is the best way to get the coils of the stepper motor disconnected
from the rest of the circuit when it is off?

I have now read quite a bit about relays, optocouplers, solid state
relays, mosfets etc.

So for me as a hobbyist / electronics layman it is hard to assess what
would be the best / easiest solution to the problem.

I would be very grateful for helpful tips.

Rate this post
 • ▲ useful ▼ not useful
Mister G. wrote:
> I am therefore concerned that this can damage the controller
It depends on the controller, but usually it should be able to handle
the voltage and the current if its not higher as the usual working
range. So at first I would do some simple tests and check wether the
supply voltage overrates the battery voltage and the following step down
when moving it powerd off.

> What is the best way to get the coils of the stepper motor disconnected
> from the rest of the circuit when it is off?
If you want to get it really disconnected with no concern about voltages
and currents you must use a mechanical relay. Becaues an open mechnical
contact is the only mean to get absolutely no current back into your
circuit.

 1  decoupling  2  diode  3  + -------o------>|---o----.  4  | |+ |  5  stepdown === |  6 battery | | |  7  µC ----------+-> driver ===> motor  8  | | |  9  - -------o-----------o----' 

> what would be the best / easiest solution to the problem.
The "easiest way" would be: do nothing. Most of the devices you can buy
are like that.

The "easy way" would be to seperate the supplies of the motor driver and
the logic with a diode, so that the inducted current cannot find its way
to logic. And if the inducted voltage then overrates the motor driver
you can add a resistor with additional circuit (like a crowbar) to
absorb the energy.

The "hard but absolutely safe way" would be the mechanical relays.

: Edited by Moderator
Please log in before posting. Registration is free and takes only a minute.
Existing account
 User name or e-mail address Password
Do you have a Google/GoogleMail account? No registration required!
Log in with Google account
No account? Register here.