Inktober Project 2019 – Post 3

Setbacks and Homing Issues

Status Update

Read Post #1 and Post #2 here

I have a breadboard version of the controller running. So far, it can control the motion of the pen, feed roller and check the homing (reed switch).

Broken Gears.

I noticed a little clicking sound and rough motion when running the motors. Looking carefully, I could see that the gears on the motor shafts were both cracked.

After searching around, I found that this is a common problem. The gear is pressed on and 35 years of stress probably cracked it. Fortunately someone sells them via Shapeways On Demand printing service.


At startup, the machine needs to home the X axis and locate pen #1. It does this in a clever way, so that it does not require any motors or sensors on the pen carriage.

The pen carriage has a little bar magnet. This will only trigger the reed switch in one orientation of the rotating pen carriage. Each time the carriage goes to the left end a little metal tab pushes the carriage 12th of a rotation.

As far as I can tell, on the first move, it moves to the left the full width of the X travel. If the carriage started in the middle of travel, the motor just stalls for the rest of the move. It then checks the reed switch. If the switch is not activated, it backs off to the right, comes back, rotating the carriage another 12th turn. It checks the switch and repeats the sequence until the magnet is detected.

Here is a video of that.

Grbl Homing

A standard Grbl homing sequence is not going to work. It will go to the end, not see the switch and fail. I will need to program this multi-move, check, repeat sequence into Grbl.

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