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Topic: Stepper motor rotating by hand: Arduino protect (Read 4177 times) previous topic - next topic

Skino

With an Arduino and an A4988 stepper driver I would like to operate a stepper motor. This motor operates a hand wheel, which is often operated by hand.
Can the generated electricity damage the A4988 and if so, what can I do? Insert diodes in the cables?




Robin2

I don't know the answer but it may be better to change the title (by editing your Original Post) to "Will manually rotating a stepper motor damage an A4988"

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

rpt007

#2
Oct 16, 2016, 11:32 pm Last Edit: Oct 16, 2016, 11:39 pm by rpt007
Quote
Can the generated electricity damage the A4988?
YES - when a motor is turned by an external force - in this case manually - it will function as an electrical generator. This will then drive current backwards into the driver and - if the power is high enough - it will destroy your driver.

In one of my projects I am running two stepper motors. One of the motors can be turned manually - and as I know that Murphy's laws are always valid - a protection was needed.

The solution: Schottky diodes.
In my first PCB version I used discrete 8 diodes per motor. Then I found another, more convenient solution (less devices and less soldering) as TI has developed an 8 diodes array in one chip.

See attached the schematics:

Just attach this array or discrete Schottky diodes to the coils M_A and M_B.
Before you ask:
Did you really read and understand How to use this forum ?
AND:
Do you have already some solution or is a part of the problem sitting in front of the screen?  :)

MarkT

But surely all motor drivers already include such diodes, otherwise they would fail from inductive kick-back?
The current "driven backwards" just goes into lifting the DC rail voltage.

A problem you have to address is having the DC bus voltage pushed too high - for this
a voltage clamping circuit is needed capable of handling the power involved.  Sometimes a driver will
have a "braking chopper" which dumps power into an external power resistor to absorb the braking
energy from a DC motor (but these are used in stepper drivers to my knowledge).

Usually its easier to ensure the speed of manual rotation can't generate a high enough voltage
to exceed your driver's ratings - make the normal motor top speed faster than manual turning can
manage...
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

MorganS

A stepper motor is the wrong solution. If the stepper is operating, then it's locked. Manual input should not move the shaft. If it's switched off then what are you trying to do?

If this is something like a volume knob that can be adjusted by hand and by remote control, then a DC motor and a slip clutch is usually used. The imprecise positioning of the DC motor is never a problem because you read the knob position from its pot, not by taking a defined number of steps.
"The problem is in the code you didn't post."

lbrutti

Hello,
Sorry for reopening the post, but i'm working on a similare system.

I need to set a parameter by turning a wheel by hand (and sensing the rotation with a rotary encoder) , eventually store the setting and recall it.

I want to give user feedback by putting back in position the wheel.

here's a sketch:



I'm planning to use a stepper (switched off unless the user pushes the recall button) with this driver:


Do you think it's a bad idea?


Robin2

I'm planning to use a stepper (switched off unless the user pushes the recall button) with this driver:
You have not said what stepper motor you propose to use?

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

lbrutti

You have not said what stepper motor you propose to use?

...R
Hello,
I bought this kit:
https://www.plexishop.it/it/driver-per-motori-stepper-uln2003.html

Thanks for the reply

Robin2

That looks like a 28BYJ... stepper motor. There are dozens or hundreds of Forum Threads about them although I have never used one myself. My guess is that you won't have any electrical problems doing what you propose.

Make sure you read all the earlier Replies in this Thread carefully.

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

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