Against the Clock (Revisited)
Introduction: Against the Clock (Revisited)
A time trial cyclist with servo motor controlled time indicators (wheels), representing the hours and minutes with the cyclist pedalling on the hour. A combination of 3D printing and perspex controlled by a Microbit and RTC.
I revisited a previous project Against the Clock due to a number of changes and modifications.
No direct requirement for Neopixels, using servos instead of steppers, improvements to the gear mechanism for the cyclist. Addition of hand positioning via hall effect switches. Simplification of time setting.
I decided to leave the dials much the same and not add numbers or spoke lines as I felt it detracted from the look of the project.
Supplies
Hall effect IC (A3213EUA-T) or equivalent - Qty 2
Resistor 2k2 - Qty 2
Capacitor 100nF - Qty 2
3 pin screw terminal - Qty 2
RTC DS3231
Battery CR1220
Pinbetween
Servobit (16 way multi servo controller)
Geekservo Building Brick 360 rotation servo - Qty 3
3mm drill bit
5mm drill bit
3mm Spherical magnets - Qty 2
M3 bolts - Qty 4
M2.5 bolts - Qty 6
Brass tubing - 5mm x 5mm
Brass tubing - 6mm x 5mm
Step 1: Cyclist
The original cyclist had a bit of a wobble as the pedals went around due to the use of thin aluminium sheet and a plastic axle. 134
In hindsight a thicker piece of metal/perspex or two thin pieces separated by a space.
However, finally settled on a slip bearing made from 2 pieces of brass tubing.
The outer tube is a press fit into the aluminium plus a spot of glue and the inner tube slid onto the axle this is pushed through and aligned with the outer tube. This stops the wobble and eliminates the wear on the axle.
Although, the cyclist is not intended to move continually but for a short period on the hour.
Step 2: Servos
The broad single spokes coupled with the analogue function of time on minimalistic clock faces negates the requirement for precise positioning, repeatability and reproducibility being more important in this regard.
Due to a lack of real time feedback positional drift can occur over time resulting in time shifts.
In order to compensate for this automatic homing is incorporated by fitting a hall effect switch at the 12 o'clock position on both dials.
This positions the hands in the vertical position enabling setting from a known reference.
This occurs at switch on or after a reset.
Additionally, to compensate for positional drift the hour hand will auto home every 12 hours and the minute hand will auto home every hour.
Three servos in total are used one each for Hours, Minutes and the Cyclist.
Step 3: Hall Sensor
The Hall Effect sensor is used to generate a digital signal in the presence of a magnetic field.
This is enabled by fitting a spherical magnet in the clock hand and the Hall sensor in the dial at the 12 o'clock position.
In the absence of a magnetic field the sensor output is logic 1 and with a field logic 0.
The output of the sensors are connected to P0 (Hours) and P1 (Minutes).
The sensor has an open collector/drain and therefore requires a pull up resistor (2k2) and a decoupling capacitor (100n), across the supply both of which are mounted locally to the sensor using a 3 pin terminal which is mounted to the back of the dial. Each sensor uses 3 wires V+, 0V and Output.
Mounting the sensor entails removing the screw/bolt at the 12 o'clock position and drilling two 3mm holes on the back panel coincident with the pillars at 7.5 minutes past the hours and 37.5 minutes to the hour. Two additional 5mm holes are drilled behind the clock face to enable the sensor wires to be routed behind the main panel.
The original fixings were cheese head allen key type, but when the hand distance was adjusted for detection this resulted in the hand being closer resulting in the hand hitting the bolt head.
In order to resolve this the cheese head bolts were changed to countersunk head.
The sensor has the leads pushed through the hole on the clock face and screwed into the terminal block and a little hot glue applied to hold this and the trailing wire in place to exit the back panel via a 5mm hole.
The sensor is turned up at 90 degrees with its face pointing toward the magnet.
A 3mm hole is drilled in the hand at the same vertical posiition as the sensor to accept a spherical magnet and this is glued in place.
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Step 4: Coding
The application is created with Makecode. 552