From the Loftsmith Workshop

Right-angle knob drive for 6 mm D encoders (Hobson joint)

Lets you turn a rotary encoder from the side when the knob has to sit at a right angle to the board. Two orange drums are linked by a ring of thin rods inside a dark L-shaped frame, with a ridged grip on the end. Change the rod count or the shaft angle to suit your layout.

10 parts · 49 g · 43 × 101 × 100 mm

by Loftsmith Workshop

L-shaped dark frame holding two orange drums joined by pale rods, with a ridged knob, above a small green board
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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

  • frame right · PLA · Split face down (printRotate 0, -90, 0); 85.6 x 86.4 x 21.5 mm

    ~9 g, ~18 min (build report). A 13 mm arm joins the two 21 mm bearing bosses. There are hex pockets for 4 M3 nuts and one mounting ear. The half-bore roofs have a 45° diamond relief, so no supports are needed.

  • frame left · PLA · Split face down (printRotate 0, 90, 0); 85.6 x 86.4 x 21.5 mm

    ~9 g, ~18 min (build report). Mirror of the right half, with 4.7 mm counterbores for the M3 socket heads and the second mounting ear.

  • input drum · PLA · Bore face down; 29 x 29 x 61 mm

    ~13 g, ~26 min (build report). The drum, 10 mm journal and fluted 26 mm knob with an index groove are one piece. The 45° cones need no supports.

  • output drum · PLA · Bore face down; 29 x 29 x 60 mm

    ~12 g, ~25 min (build report). The 19 mm hub has a 10 mm deep 6 mm D socket with a chamfered mouth.

  • rod ×6 · PETG · Flat side down (printRotate 0, 90, 0); 37.2 x 37.2 x 4.3 mm each

    ~1 g and ~6 min each, ~6 g and ~36 min for all six (build report). The rods are identical 5 mm L-rods with 34.7 mm legs, bent at the shaft angle. Print them in PETG because they slide in the drum bores. The script declares them as rod 1 to rod 6 only so that each one follows its own path in the anim

Print settings

Layer height
0.2 mm
Walls
2
Infill
15%
Supports
None. Every part prints without supports in the orientation given.
Notes
The build report gives about 48.9 g and 2 h 3 min for everything: 2 frame halves, 2 drums and 6 rods. Print the frame halves and drums in PLA and the rods in PETG. Put the frame halves split face down, the drums bore face down and the rods flat side down.

Hardware

  • 4 × M3 x 16 socket head cap screw · Closes the two frame halves, two beside each journal.
  • 4 × M3 hex nut · Pressed into the hex pockets in the right frame half.
  • 2 × M3 standoff · Mounts the frame ears to the board. The holes are 32 mm apart, on a line through the output shaft and square to the input shaft. The standoffs are 32 mm long for the modelled encoder, whose shaft tip
  • 2 × M3 screw for the standoffs · Length to suit your standoffs.
  • EC11-type rotary encoder or pot with a 6 mm D shaft (4.5 mm across the flat) · Not included; this is what the output socket drives. Use a 1/4 in hex shaft instead with the hex output option.

Assembly

  1. Press the four M3 nuts into the hex pockets on the outside of the right frame half.
  2. Slide one leg of each of the six rods into the output drum's bores. All rods are identical, and either leg can go in.
  3. Hold the input drum at the shaft angle to the output drum, with its bores in line with the free legs. Slide each rod in or out until its free leg lines up with a bore, then push the input drum onto all six legs.
  4. Lay the drum and rod set into the right frame half so both journals sit in their half-bores and both cones sit in their seats.
  5. Put the left half on top and drive the four M3 x 16 screws from the left side into the nuts. Turn the knob: both drums should spin freely, with about 0.3 mm of end float.
  6. Fit two M3 standoffs on the board, one each side of the encoder, 32 mm apart. Lower the frame so the 6 mm D socket slides over the encoder shaft, and screw the ears to the standoffs.

Good to know

  • This has not been printed or tested. The Loftsmith engine checked the geometry and motion, but friction and fit after printing are untested. Print one drum and one rod first, then adjust the clearance slider (0.2–0.8 mm on diameter, 0.4 mm default) until the rod slides freely without rattling.
  • It is not print-in-place. The two frame halves screw together around the drums, and the rods go in by hand.
  • The frame mounts only to the board, through the two ears. Panel mounting is not modelled. With the 6 mm D input shaft option, the shaft sticks out 16 mm past its collar for your own knob, but how it passes through a panel is up to you.
  • The rated torque is about 0.17 N·m at the defaults. That figure is a PETG rod-bending estimate with a safety margin, not a measured value. It is meant for knobs, encoders and pots, not for driving loads or forcing a pot past its end stop.
  • Some combinations of extreme settings, such as 3 rods of 4 mm, fail the strength check. The check shows FAIL in the Studio when that happens.
  • The output turns 1:1, but in the opposite rotational sense when each shaft is viewed from its own end. If your encoder counts the wrong way, swap A and B in your code.
  • The encoder and its height above the board are an approximate EC11 envelope. Measure your part and set the standoff length to match.
  • Expect some play at the knob. It comes from the rod clearance, so a bigger clearance means more play.
I printed this Remix

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