Video

In many circumstances CNC machines may need to have two motors on a single axis. One of the reasons for this is that the two motors will act together so the gantry will not rack: meaning that one side is pulling more than the other side because the end mill may be under load on one side of the machine. The side with load could be pulling against that load causing the gantry to be uneven along the length of the machine. Because of this, two motors would be used in some circumstances where you have the motors connected to mechanics on both sides so each side is pulling or pushing in the same exact way.

If these motors are being mounted in opposition and the mechanics are identical on both sides, you'll need the two shafts to be rotating in an opposite matter. In some cases you can resolve this mechanically, by taking your drive mechanics and changing the way the mechanics are set up so maybe the chain or pulley would be on the top or bottom; however, in many cases this is not possible so you'll need the motor to be turning in the opposite direction.

To put two motors and two drivers on a single axis, you'll take the particular axis pins (step and direction) and you'll need to wire them to both of the drivers, but in that scenario both motors will be turning in the same direction because the direction signal from the breakout board will be high in one direction and low in the other direction and they'll both be sharing the same signal. What you need to do is invert one of those signals coming from the breakout board (taking the direction signal from one of the drivers and wiring it to a hex inverter to invert one of the signals), so when the direction is high in one direction for the other driver, it will be low on the other one and vice versa for the opposite direction.

The hex inverter only needs five volts ground and a direction signal. The step signal is going to stay the same because they both need to maintain the same number of steps. In the video you will see a demonstration of the motors moving in opposing directions. Hopefully this video will be useful to anybody who needs to invert the direction of one motor on a dual-motor axis.

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