Introduction: Flexible Project Battery Power Supply (PSU) for L0Cost Robots
Power supplies for robots usually involve batteries of various kinds. This is a base level design which uses a common buck converter, a switch and a 3D printed container to hold batteries and attached them to a robot. These are simple designs created on TinkerCad, links for these in the steps below.
The design is intended to power both a controller card, with the buck converter adjusted to a suitable voltage, and also directly to higher voltage/current users such as larger servos and stepper motors as well as drive motors. In order to do this, two batteries are connected in series, generating around 7.4V. This is too high to supply the smaller SG90 servos which may burn out with the higher voltage and must use the power regulated by the buck converter.
The buck converter has an onboard LED which serves as a power on indicator if the display isn't used.
Supplies
Buck boost converter - the pictured one is readily available, based on an LM2596S
STL files to 3D print desired battery box
Matrix board as pictured
Inline connectors for your batteries - make sure you purchase the opposite gender to your batteries
Miniature switch
Dupont PCB pins - 4 pairs used in the design but as many as required.
Red and black hook up wire
Low cost seven segment led voltage display
Lithium Polymer Batteries to suit
Step 1: Choose a Design
Each battery box is intended to be able to be used standalone as a power source for a breadboard project or attached to a robot chassis.
The first one is a basic box which cab be attached via the slotted holes in the base. It has two tabs which allow an elastic band to be stretched across to hold batteries in if required. It has an optional fitting for a voltage display. It is available on TinkerCad here https://www.tinkercad.com/things/bbKKeeQVtrg
The second one is more open and has a mount on the front to attached a camera, in this case it was an ESP32-CAM module. It is available on TinkerCad here https://www.tinkercad.com/things/hskkgWnIRIg
The third is very similar to the first but has an additional two tabs for mounting vertically, when a retaining elastic band might be needed, again with the optional voltage display. It is available on TinkerCad here https://www.tinkercad.com/things/ape87LFGbST
Attachments
Step 2: Assemble the Circuit
The circuit is assembled on a small offcut of matrix board, which I always save from other projects. The picture shows it with two holes drilled to accommodate attachment to the box. Flying leads connect the matrix board to the buck boost board, measured to fit the box design used, using red and black hook up wire to make the connection polarity clearer. Pins are inserted in pairs, two soldered to the switched battery supply, two connected to the output of the buck converter, two on the negative/ground switched connection and two on the ground/negative return from the buck converter.
Two pin connections bridge a cut in the circuit board and must be joined with a solder bridge.
The switch is intended to be used as push to connect, a multimeter must be used to ensure that the switch pins which are joined when off are on the same matrix board track.
Before use, the buck converter is connected to a suitable supply and the output measured and adjusted to the required voltage, commonly 5v for most modules, but some may want 3.3V.
The intention for this battery box is to be used with Lithium Polymer (Lipo) batteries to provide a compact power source and these can come with a variety of connections. Suitable fly lead connectors must be sourced for fitting to the board so that it will connect to the batteries safely and securely.
The batteries are intended to be used in series so a positive to negative join must be made in the fly leads.
Step 3: Test
Inspect the soldering and check that positive and negative lines have independent and isolated routes. If cautious, connect up the battery connectors to a bench power supply and test before connecting batteries for real. Check that the required voltage output is available from the circuit before connecting to a robot. If the voltage display is used, calibrate it with a trusted voltmeter first as they can be a bit out occasionally!
Step 4: L0Cost Robots
The power supply was originally designed for reuse in many small robotics projects under the banner of L0Cost robots, targeted at budgets under $20, which are finally been published here as instructables. This is very much a first step project upon which others can be built.