Monthly Archives: March 2017

seXY – computer-controlled mechanism for a new clock

s e X Y

Computer-controlled mechanism for a new clock

seXY is a motorized mechanism that under computer control can move a carriage slide in two separate axes: up to 380mm (15″) in the X-axis (side to side) and 350mm (13.5″) in the Y-axis (front to back). A huge “design space” to play with! My intention is to mount a head to the slider equipped with a servo that engages either a pen or an eraser… More to come on that front!

In the following video, the left and right steppers are being controlled by the micro-controller which is just moving the slide to and fro the X and Y axis, and the four diagonals.

seXY: Stepper-driven X-Y mechanism

So, this weekend CNC project was largely inspired by an interesting product called AxiDraw,  that is described as “the personal writing and drawing machine that mixes the precision of robotics with the warmth of a hand-drawn note.”  I was primarily fascinated by the control belt arrangement that allowed the two steppers to be stationary. This avoids all the complications of creating wiring harnesses that have to flex with the machine movements.

It appeared from the video and other similar designs that the two steppers are fixed at either end of the x-axis and that axis movement is achieved by moving BOTH. This belt arrangement has an interesting effect. When both steppers turn in the same direction, the carriage slide moves along the x-axis. When the steppers move in opposite directions, the carriage slide moves along the y-axis. If either stepper is stopped, the carriage slide moves along a diagonal.

Neat, huh.

So I decided to design and build one.

Continue reading

Dimmer Not Dumber II: Servo-controlled light fader

Introducing the “Dimmer Not Dumber” II

A novel approach to fading line voltage lights!

This video shows me triggering the unit and then at the end, applying a reset signal. The unit is programmed to climb slowly to preset light levels upon repetitive triggering (10%, 20%, 30%, 40% and 100%). The reset signal applied at the end [44s] slowly fades down the light intensity to fully OFF.

A client wanted me to control the brightness of two sets of residential 110v pot lights. The only experience I have in controlling line-powered equipment is through using relays and opto-isolated solid state switches. However, these just provide simple ON/OFF control; and dimming lights is a whole different ball of wax! Plus, I did NOT want to mess with mains voltages!  There are devices on the market to do this but they are a) expensive, b) require electronics connected to the 110v load side and c) require real-time software to control (see discussion below). I wanted a simpler solution that used off-the-shelf residential electrical components, used simple electronics and gave me complete electrical isolation.

So, I came up with the “Dimmer Not Dumber” light fader design.

In this design, a servo motor is connected to the shaft of an unmodified residential light dimmer (Levitron, I believe) via a simple gear pair. This dimmer has a control shaft that rotates about 320 degrees to fade between full OFF to full ON. In addition, pushing the switch knob turns the whole unit ON and OFF.

As servo articulation is typically a maximum of 180 degrees, a 2:1 gear pair means that the full range of the servo translates into a complete rotation of the dimmer shaft. Control of the servo position therefore allows full control of the intensity of the light, so now all I have to do is connect the servo to a micro-controller and voila!  Full control of the light intensity and complete electrical isolation!

The Dimmer Not Dumber II version now includes an Arduino Nano, input conditioning for 5 – 24V triggers and a 5V buck converter. An 8-tooth gear attaches to the electrical fader’s control shaft and tightened with a small set screw, while the larger 16 tooth gear attaches to the servo using a plastic servo horn.  All electrical components are located within pockets in the base attachment plate while the upper plate holds the servo and has holes to access the pair of 3-pin servo connections and the 4-pin screw terminal block for external connections.

The body of the unit is made in two parts: a 12mm HDPE base attachment plate and a 6mm HDPE upper plate servo mount. The base and upper plates are attached using 3 3mm Allen-head bolts. The electrical fader mounts inside an electrical box as normal, and the Dimmer Not Dumber II unit bolts to the dimmer using the normal screw holes used for fascia plates.

Dimmer Not Dumber II: showing top face with the two servo pins and the external connection screw terminals.

Dimmer Not Dumber II: closeup of the two servo connector pins and the screw terminals for 9-12V, Ground, Trigger and Reset connections

“Dimmer Not Dumber” works like a charm, both in the light and the dark!

Continue reading

CYCLOPS: servo-controlled Mechanical Iris

It’s been a while since I’ve posted – I have been busy though – and even longer since I posted something not related to a clock!

So, behold… CYCLOPS – The Mechanical Iris!

The video above – taken from the front – shows the completed CYCLOPS Mechanical Iris opening and closing as the servo runs back and forth. The video below – shot from the back – shows the mechanical linkages between the outer gear ring and the “petals” of the iris, and how the assembly operates to open and close the iris.


The CYCLOPS Mechanical Iris is made up of a face plate and five pivoting “petals”, each linked to a large rotary gear ring. The petals are carefully shaped to allow them to open and close a central iris that is 200mm (8.6″) in diameter. A 5:1 gear connects the outer ring to a small metal-gear servo motor mounted to the face plate. As the videos show, as the servo rotates through 180 degrees, the petals move so that the iris fully opens and closes.

Mechanical Iris: with outer gear ring and linkages to each of the 5 petals

Mechanical Iris: showing 5 petals in open position

Mechanical Iris: showing 5 petals in closed position

Designed and built as a proof of concept, the CYCLOPS Mechanical Iris was made quickly to test geometries and mechanical operation. It was designed using SketchUp with CAM operations using SketchUCam, and cut on my CNC machine  The face plate is cut from 12mm baltic birch, while the petals, linkages, outer ring, servo mount and servo gear are cut from 6mm HDPE (High Density PolyEthylene).

The initial design was for a proof-of-concept mechanical door to a “locked” compartment. Upon receipt of a trigger signal, the iris was required to open to allow access to the compartment behind and whatever it contains. While the POC was very successful, a number of design changes will be made to improve performance and usability. In this design, I incorporated three different linkage points on each petal, each a different distance from the pivot point, to test different lengths and designs of linkage arms. Tests showed that only the outermost (furthest) connection point was necessary, so the others will be removed. A simple curved linkage allowed for some spring in the mechanism that helped to fully close the iris, and this design element shall remain. The teeth of the outer gear ring covered an arc of 90 degrees. This proved to be in excess of what was needed and a sweep of only 45 degrees will be used. Additionally, the face plate will be redesigned with a deeper pocket to accommodate the outer gear ring and servo gear. This will also allow for a simpler servo mount and gear ring restraint. Also, the new face plate will also have simpler attachment points to the hidden compartment to make it easier to install.

Neat huh?