From the Loftsmith Workshop

Whiteboard wall plotter: 28BYJ-48 clip-on motors, SG90 lift

Turns a plain whiteboard into a drawing robot. Two small motors clip onto the top corners and pull strings to a marker holder, while a little servo arm lifts the pen off the board. Set your board's width and height and the marker size.

7 parts · 142 g · 493 × 56 × 472 mm

by Loftsmith Workshop

Whiteboard with two corner motor clips, a top electronics plate and a marker carriage hanging on strings
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No adjustable sizes

Ask for the sizes you want to tweak, e.g. “make the width adjustable”.

Change it in the Studio

Parts

  • motor-clip ×2 · PLA · On its side, U profile flat on the bed
  • spool ×2 · PLA · Wide flange down

    Press onto the motor's flat-sided shaft; tie the line through the small hole.

  • gondola · PLA · Board side down, with a brim and supports

    It stands on the two dome tips, so it needs supports (up to about 4 g) and a brim. Press an M3 nut into the slot beside the marker tube.

  • lift-arm · PLA · Flat, collar pocket up

    Glue onto the stock horn with the collar around the hub.

  • controller-hub · PLA · On its side, U profile flat on the bed

    Melt in 8 M2.5 heat-set inserts before mounting the boards.

Print settings

Layer height
0.2 mm
Walls
3
Infill
15%
Supports
Only the gondola, with a brim; the other parts need none.
Notes
3 walls keep the clip lips and insert posts strong.

Hardware

  • 2 × 28BYJ-48 5 V stepper with ULN2003 driver board
  • SG90 micro servo · With its tab screws and single-arm horn
  • Arduino Nano
  • 3 × M3 x 16 screw or thumb screw + M3 nut · Frame grip, one per clip and one in the hub
  • 4 × M3 x 10 screw + M3 nut · Motor ears to the clips
  • M3 x 12 screw or thumb screw + M3 nut · Marker clamp
  • 8 × M2.5 heat-set insert
  • 8 × M2.5 x 6 screw · Driver boards
  • 2 × Small zip tie · Hold the Nano
  • Braided fishing line, about 0.5 mm · About twice the board's longest diagonal
  • 2 × 5-wire JST-XH extension lead · The route needs about 370 mm per motor on a 900 mm board, more on wider ones; stock leads are often shorter
  • Servo extension lead, 1 m · About 85 cm with slack on the default board; longer for bigger boards
  • USB cable + 5 V 2 A supply · Run a separate 5 V lead to the driver boards
  • 10 × Dupont jumper wires · Nano to the driver boards and servo
  • Cyanoacrylate glue · Lift arm to horn

Assembly

  1. Melt the 8 M2.5 inserts into the hub posts, screw on both ULN2003 boards and zip-tie the Nano between them.
  2. Bolt each motor behind a clip with 2 M3 screws and nuts, wire cover pointing down over the bridge, then press a spool onto each shaft.
  3. Fit the M3 grip nuts. Slide the clips over the top corners of the board and the hub over the middle, then tighten the grip screws from the front.
  4. Run the motor leads straight down from the covers and along the top of the frame. The hub holes are 6 mm and the JST plugs are wider, so release the pins from each plug housing, thread the wires through and reseat them in the same order, then plug them into the drivers.
  5. Screw the SG90 onto the gondola posts. Fit the horn, set the servo to the pen-down angle, then glue the lift arm on top.
  6. Fit the marker, tie a line from each spool to the gondola, plug in the leads and wind the gondola to the top centre.

Good to know

  • Not printed or physically tested yet: every number here comes from the model's checks and estimates. Print one part first and test the fit.
  • The domes ride beside the pen line, but they can still brush ink where a vertical stroke or a crossing passes under them.
  • Motor torque and the clips' grip are estimates (10 mN*m needed at the top against about 20 mN*m usable, and 15 N of friction against about 3 N of pull). Check that the clips stay put and the motors don't skip near the top corners.
  • The servo horn hub (7 mm), ULN2003 hole spacing and frame thickness are typical values. Measure yours and set them with the sliders.
  • The clips and motors need 4.8 mm between the frame back and the wall, at the default 18 mm frame. A board hung flush on the wall needs spacers, and there must be room above the top edge for the motors and hub.
  • Pen pressure is not modelled: the pen-down check is geometry only, so tune the nib with the clamp screw. Power the motors from the 5 V supply, not through the Nano's 5V pin.
  • Firmware and drawing software are not part of this design.
I printed this Remix

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