stepper motor holding torque ?

Other Hardware Motors, Mechanics, Power and CNC
1

Hi everyone

My first post here, I hope someone can help me out
I am building a project with
Arduino UNO
CNC Arduino Shield V3
qty 4 of DRV8825
using 4 drivers as I have cloned X to use 2 stepper motors on this X axis, 2 x jumpers fitted
At the moment I have no jumpers fitted to the multisteppers but can fit if needed

Stepper motors are 23LM-C343-14V made by MINEBEA
These have 6 wire plugs fitted but I am told that I only need 4 Orange-Blue-Yellow-Red
The spec on these motors I have found here - Minebea Stepper Motor Specifications

I have an mains AC / DC external power source connected to the shield

I am running latest GRBL and latest Universal G Code Sender UGS Platform actually downloaded today so up to date

The 4 motors are to not to drive a CNC machine at this time, I am building a CNC but that is another project, This project is to operate 4 seesaw type balances with small archery targets mounted on them, so as 1 target goes up the other comes down, so I can have 8 targets going up and down in a sequence, I hope that makes sense ?

I have the 4 motors all working lovely on the bench, they all turn exactly as they should do, for the correct time, and in the right directions, they have enough power to lift the targets as I want them to so I am happy with that

Now the problem is that I need the targets to stay up, until the programme moves them back down, I was expecting the stepper motors to have some electrical torque braking when they reach their designated travel points

Quite simply the motors when powered off at the end of travel seem to have little holding power and slowly drop down, have I missed something or is there an easy (or even complicated) way of holding the stepper motors I have in position for say 8 seconds then powering the target down ?

Thanks for your help in advance, I hope I have added enough info, if not please let me know

2

ArcherToad:
Quite simply the motors when powered off at the end of travel seem to have little holding power

Stepper motors are not intended to be powered off. They need more-or-less full power even when stationary if they are to hold position.

...R
Stepper Motor Basics
Simple Stepper Code

3

that is what I thought, how do I keep power on as it seems to be switching off

or I just had a thought, I have only been using the jog and test function, would the motors act differently on a programme ?

4

ArcherToad:
how do I keep power on as it seems to be switching off

I don't know. GRBL is a very complex program and so is UGS. My guess is that it is UGS that is causing this behaviour. There may be settings that can be changed.

You might find it easier to get info from a CNC Forum where people are familiar with GRBL and UGS - this Arduino Forum is mainly for helping people write their own programs.

...R

5

It may be due to power reduction on standstill, often implemented with steppers to reduce self-heating(*). If
the motors don't have enough torque, you need bigger motors or more gearing.

(*) its common to drop the current to about 50% after a fraction of a second without step pulses to save power.
Since the holding torque is much bigger than the dynamic torque at high speed, this is often fine as the limiting factor is the high speed torque in most setups. You may be finding the limiting factor is stationary torque.

6

MarkT:
It may be due to power reduction on standstill, often implemented with steppers to reduce self-heating(*). If
the motors don't have enough torque, you need bigger motors or more gearing.

In this case I suspect it is more likely that UGS is deliberately disabling the drivers to allow manual movement of the motors.

...R

7

There are G-code commands to de-power the motors. Is it possible that you have those commands inside your G-code that you are sending? M18, M85 and M85 are the relevant codes for my 3D printer.