Build Guide: Whiteboard Marker Holder

Introduction

The whiteboard marker holder attachment lets your Rover draw on whiteboards and paper using a standard marker. The shell clips over the front of the Rover, and a micro servo swings the pen holder down to put the marker on the ground, then back up to lift it off. This guide walks you through printing and assembling the attachment step by step.

Before you start:

• Use a standard (positional) micro servo. The servo turns to an angle: 0 holds the pen up and -90 puts it down. A continuous rotation servo would keep spinning instead.
• Calibrate the servo before you fit the horn. The horn has to point straight up when the servo is at 0, or the pen won't line up with the ground. Step 3 shows how.

What You'll Need

Parts:

• 1x Micro Servo
• 1x Single-sided servo horn (from the servo's accessory bag)
• 2x Servo mounting screws (from the servo's accessory bag)
• 1x Servo horn screw (from the servo's accessory bag)
• 1x Whiteboard marker

Tools:

• Phillips Head Screwdriver

Download the free STL files

ThingiversePrintablesMakerworld

Don't have a 3D printer?

Buy Pre-Printed

13D Print Your Parts

• 1x Robot Shell (the curved clip with the servo box on top)
• 1x Pen Holder (the L-shaped arm with the marker ring)

2Install the Servo

• Hold the shell with the curved clip facing forward and the servo box on top.
• Lower the micro servo into the box from above, lying on its side. The output shaft goes at the back end of the box (the end away from the curved clip) and points out the open side of the box.
• The servo's two mounting tabs sit against the outside of the two posts at each end of the box.
• Fix it in place with the two servo mounting screws, through the tabs and into the small holes in the posts.
• Leave the horn off for now. You'll calibrate the servo first.

3Calibrate and Attach the Horn

• Before attaching a horn to a servo, you need to make sure the servo moves in the correct range.
• Plug the servo into the right servo port on the Rover and, in the Code Editor, set the right servo to 0 degrees.
• With the servo at 0, press the single-sided horn onto the shaft so its arm points straight up, as in the picture.
• Don't turn the shaft by hand once it's calibrated. If it moves, set the servo to 0 again before you carry on.

4Attach the Pen Holder

• Hold the pen holder with the horn-shaped pocket facing the servo and the marker ring at the top, over the servo.
• Push it onto the horn so the horn sits flat inside the pocket.
• Fix it with the servo horn screw, from the outside through the hole in the end of the arm and into the servo shaft.
• Check the fit: the arm should point straight up, and it shouldn't wobble on the horn.
• The picture shows the arm swung forward to the pen-down position (-90). Yours points up because the servo is still at 0 from calibration.

Fit and Test It

1. Clip the shell onto the front of the Rover, with the curved clip around the Rover's front end and the servo box on top.
2. Plug the servo into the right servo port on the back of the Rover. Match the brown wire to the - on the port icon.
3. In the Code Editor, set the right servo to -90 degrees. The arm swings forward and down, so the ring sits in front of the Rover with its opening facing up and down.
4. Push a whiteboard marker down through the ring, nib first, until the nib just touches the ground.
5. Set the right servo to 0 degrees. The arm swings back up and lifts the pen off the ground, with the marker lying flat above the Rover and the nib facing forward.

It's a positional servo, so the value is an angle, not a speed. -90 puts the pen down and 0 lifts it up. Lower the pen, drive the Rover, then lift the pen before you move to the next part of your drawing.

Troubleshooting

• The pen doesn't reach the ground at -90: slide the marker further through the ring until the nib touches.
• The arm isn't straight up at 0: the horn went on in the wrong position. Undo the horn screw, set the servo to 0 and refit the horn pointing up.
• Nothing moves: check the servo is plugged into the right servo port, with the brown wire on the -.
• The servo turns but the arm doesn't: the horn screw is loose. Tighten it so the horn can't slip in the pocket.

Continue Learning

Related resourceActivity: Rover Van GoghTurn your Rover into an artist with the pen attachment. Program precise movements to draw shapes, patterns, and pictures with code.

Related resourceHow to Design a Rover AttachmentA guide to designing custom 3D-printed Rover attachments, from servo allocation to print connections and gears.