Circuits

This circuit is used to create a simple “edgebot” sumo robot. Being an edgebot refers that it will repeat the same backup/turn/go forward action when it’s single edge sensor detects the edge of the ring. This version of the circuit is quite simple, and always turns the same way. Although a single sensor is all you need, it is wisest to wire up two sensors in parallel (one for each front corner of the robot), so it safely detects the edge with little chance of it falling off.

Theory of operation (How does it work?)

The circuit is based around the L293D motor driver chip, which has four high power buffers usually used to drive two small DC motors or a single stepper motor. The pair of transistors are configured as inverters that allow the inputs to the L293D to have one be “high” and the other “low”. When the switch closes, the two capacitors charge up and turn the transistors on. The transistors invert both logic signals going to the motor driver which causes the robot to reverse and back up away from the edge. Turning on the spot happens when one motor spins forward and the other continues backward. This is set by two “time-out” circuits that are tied to the transistors. By having different resistor/capacitor values on the “time-out” circuit, one motor will revert to the default forward direction before the other.

Parts for the Mini-sumo:

• 1 x L293D
• 2 x 2N3904
• 2 x 47K
• 1 x 10K
• 1 x 2K
• 1 x 1N914
• 2 x 22uF caps
• 2 x gearmotors
• 1 x 9V battery
• 1 x Switch (2 are better). Can be built from spring wire and a thick copper wire.
• 1 x Power switch
• Construction material such as sintra, steel plate, carbon fiber or whatever you prefer.

Circuit Diagrams:

Wiring Diagram of L293 Edgebot:

The reverse time here is set by the 22µF caps the 10K resistor and the 2K resistor. The difference between the two resistor values is what determines how much the sumo will turn. How high the values are will determine how long the sumo will reverse. For instance if you want it to turn the same amount but backup further then increase both values by 10K so the new resistor values are 20K and 12K.

Technical Schematic:

This is the technical layout with the transistor inverters simplified to the electrical symbol and the L293 shown as a quad of buffers. With this it should be easier to visualize what’s happening.

Dual Sensor Sumobot Circuit:

This circuit is more difficult to tweak and probably far from optimized, but if your interested here it is:

- This circuit has two edge sensors, when either sensor is hit it will start reversing then depending on which sensor was triggered will turn left or turn right.

- This works on a different principal than the edgebot circuit. In this circuit, the timing values are the same and the voltage that the capacitors are charged to determine the reverse time. By charging the capacitor through three series LEDs, the capacitor voltage is lower than the other capacitor. This means the L293 will “see” the input from this lower-voltage capacitor as a logic “low” before the other. To adjust how much the sumo turns, add more LEDs (in series) to increase the voltage drop.

Additions:

- Adding a 5 second startup timer is as simple as tying the two enable pins together and attaching a capacitor between them and ground. The internal pull up resistor will gradually charge the capacitor and enable the chip. If you need further control over the startup time either add a resistor in parallel with the capacitor to increase the startup time or add a resistor from the enable line to Vcc to decrease the startup time. Running at 9V a 22µF cap with a 2M pull up resistor give close to a 5 sec startup, voltage will effect the startup time so I advise using a potentiometer.

© Solarbotics, 2002

ShokPopper & ShokPhoto-head

You want a simple Photovore? This very tidy design by Solarbotics’ own Grant McKee is based on a technique developed by Mark Tilden - Shok architecture:

Here’s video of the test robots being tuned as a 177kB Windows Media Format (WMV) file or as a 168kB RealMedia (RM) file.

ShokPopper V1.0 (click for circuit diagram) - GrantM Aug 2001

Theory of operation:
“Shok” architecture is a technique pioneered by Mark Tilden describing controlled state changes of Bicore style circuits via chip power or enable toggling. When a Bicore circuit is powered on, it will resume a state opposite to what it was when it was powered off, this effect can either be duplicated by pulsing the enable line or by pulsing power to the chip itself. This is called “shoking” the Bicore. The power-on state can also be pre-determined by biasing the voltage across the Bicore capacitors. A photodiode attached directly across the Bicore charge capacitor will pre-bias the shoked output. The addition of tactile sensors is easily implemented by attaching a switch from the input of the Bicore to +Vdd. When the switch is closed, it forces that side high, presetting the state of the Bicore on the next pulse cycle.

Probably one of the simplest photovore circuits to date, the core circuit consists of a 6 part count and a solar-engine. Either 74AC240 or 74HCT240 will work but we recommend using the AC series for better output drive current. The ShokPopper will not work under battery power unless the enable line is pulsed.

Solar Engine to use with Shok:
The best solar-engine to use is the Miller engine. For the ShokPopper Photovore we used a Miller engine consisting of:

• CP3300uf cap
• 1381Q
• CP1µf timer cap (0.47µf will work fine as well)
• 2N2222 Transistor
• SC3733 Solarcell
• D1 1N914 Diode

The Bicore Circuit Consists of:

• 74AC240 Octal Buffer Chip
• TR100k Trimpot
• 2 x 0.22µF Capacitors
• 2 x IR1 Infrared Sensors
• 2 x RM1 Motors
• TACT2 Spring Sensor Kit (Optional)

The Miller engine switches the ground line of the circuit.

The theory of operating is very similar to that of the shok popper except that the head now only uses one motor, the photo head does not “lock” on but will continually seek for the brightest source of light. Nice effect if you want a continually seeking, dynamic device on a stationary base.

• 74AC240 Octal buffer chip
• 4 x CP0.1µF capacitors
• 100k resistor
• 2 x 47k resistors

This is a neat little one-chip circuit we originally tuned for use with our “SM1″ Stepper motors. We’ve presently sold out of the motor, but this circuit has proved to be a good unidirectional (1-way) driver for small stepper motors. Parts required are:

• 74AC240 Octal buffer chip
• 4 x CP0.1µF capacitors
• 100k resistor
• 2 x 47k resistors

(PDF Version) GIF Link
Some of you may have found the LightStorm Pummers that Mark Tilden has made using some neat looking plastics. We’ve built our own variation of the circuit, which is a dark-activated, quad-bicore pseudo-random chaos generated, dual pummer circuit.

Parts required are:

Dark Turn on Circuit

• Solarcell (SB Part SC2433)
• 1F 2.5V (SB Part CP1.0F) capacitor
• 1 Germanium Diode (SB Part D2)
• 100k Trimpot (SB Part RT100k)
• 2n3904 transistor (SB Part TR3904)
• 2n3906 transistor (SB Part TR3906)

Pummer Circuit

• 74HCT240 (SB Part 74HCT240)
• 2 x 1000uF Capacitor (SB Part CP1000)
• 2 x UltraBright LEDs (SB Part UBLED-R)
• 2 x 100k Resistors (SB Part 100k)
• 2 x 22uF Capacitors (SB Part CP22)
• 4 x 0.22uF Capacitors (SB Part CP0.22uF)
• 2 x 2 MegaOhm Resistors (SB Part R2.0M)

Pummer Circuit

• 74HCT240 (SB Part 74HCT240)
• 8 x 2n3904 Transistors (SB Part TR3904)
• 8 x CP0.22µF Capacitors (SB Part CP0.22uF)
• 8 x 1k Resistors (SB Part R1k)
• 2.2 MegaOhm Resistor (SB Part R2.2M)
• 3 MegaOhm Resistor (SB Part R3M)
• 3.3 MegaOhm Resistor (SB Part R3.3M)
• 4.3 MegaOhm Resistor (SB Part R4.3M)

Herbie1.gif & Herbie.txt - Although not a true BEAM robot, this simple schematic by Randy Sargent is small, simple, slick, and effective. My own version uses a pair of pager motors and three cells from a 9V rechargeable battery. Hard to get any simpler than this device!