Skip to main content

Home/ Robotics/ Group items tagged h-bridge

Rss Feed Group items tagged

York Jong

How to freeform the H-bridge - by Brian Hendrickson - 0 views

  •  
    Most of us are familiar with Beckingham's photovore block (also known as Chiu's). The following is a similar format used for freeforming a simple H-bridge motor driver that can be used for walkers, heads, and any other project that uses motors that requir
York Jong

A Bot With Peripheral Vision - 0 views

  • I wanted to share an adaptation of the Schead v4, that I have been experimenting with. It is (for lack of a better term) a Master/Slave Schmitt Comparitor Head (M/S SC-H). With the addition of a 74 AC 240 or two (as motor drivers) and a pair of motors, you can put together an interesting little light seeking, wheeled robot with peripheral vision.
  • As long as the light reaching the photo-bridge of the Master SC-H is balanced, then the Slave SC-H acts as a regular, lone SC-H would. So, if one of the slave photo-diodes detects more light then the other, the inverter that controls the motor on that side changes states and is now the same as the inverter of the Master SC-H tied to the same motor. This turns that motor off and the robot will pivot around the stopped wheel toward the greater light source until the light on each sensors is balanced and the motor again begins to turn.
  • I am also using SCar to continue experimenting with Stacking separate Sensor/Behavior circuits onto a robot. I will post more as progress is made.
  • ...9 more annotations...
  • The diodes between the  photo-diodes create a constant voltage drop between the inputs of the inverters. They cause  a dead band to exist between the thresholds of the two inverters. In a way they cause the circuit to act like a kind of window  comparator. Without these diodes both inverters would always be in the same state. With them, there is a small range where their outputs are in opposite states.
  • The Slave section has only two diodes (or one LED) between the photo-diodes. This makes it respond to smaller differences in light levels than does the Master part of the circuit
  • Basically, what I did was to stack one SC-H on top of another
  • I?m using a 74 HC 139 to direct the outputs of the M/S SC-H circuit to the appropriate motor(s)
  • Cheesy works very well. I?ve had fun making him chase a spot of light from a flashlight around on the floor. He has even been able to detect and react to the flashlight spot on the floor of the brightly lighted lab where I work.
    • York Jong
       
      Stacking separate Sensor/Behavior
York Jong

BEAM Pieces -- Integrated circuits - 0 views

  • 1381s are CMOS voltage-controlled triggers -- these "gate" a source until the voltage is above some "trip" limit, at which point it is allowed onto a third pin
  • We use them as 3- or 5-volt triggers
  • This chip is often considered the heart of Nv net technology
  • ...22 more annotations...
  • The '240 is often called "the bicore chip," because we can take advantage of the 240's inverters to turn a single 74*240 into a bicore
  • The '240 also has tri-state outputs, so an enable line can be used to turn its outputs on and off simply (good for adding reversing capability to a 'bot).
  • any *cores built with a 74*04 will require additional logic "downstream" to amplify the current to levels sufficient to drive a moto
  • Schmitt triggers can't easily be used in suspended bicore implementations
  • use its buffers as little current amplifiers
  • it is usable for either grounded or suspended bicore designs (but better for suspended)
  • 74HC/HCTxx non-buffers (74HC14 or 74HC04) draw about half of the current consumption, and have about half the drive current compared to HC / HCT buffer chips (74HC240 or 74HC245). Non-buffer chips are thus better for oscillators, say Nv and Nu applications; they are not suited for use in driving motors.
  • 74AC is best suited for motor driver applications with all inputs driven rail to rail.
  • The '245 is an octal buffer chip, and so has 8 channels of buffering power available for our misuse. This chip was designed for data transmission uses, but we'll misuse it as a motor driver chip
  • The '244 provides us with 8 (thus the "octal") buffers, enableable in banks of 4. This is a very useful chip for amplifying small currents
  • it can drive up to 4 motors in 2 directions each, or you can "buddy up" inputs and outputs to drive fewer motors at higher current
  • it can drive up to 4 motors in 2 directions each, or you can "buddy up" inputs and outputs to drive fewer motors at higher current
  • If you can't find 1381s locally, you might have better luck finding its European cousin, the TC-54 -- for details on it
  • Note that if you need more than about 200 mA per motor, you'll need to use an H-bridge, or some similar motor driver
  • The ideal BEAM circuit would use a low (2V-3V) voltage core and sensors combined with level shifting high (5-6V) volt motor drivers to maximize efficiency.
  • 74ACxxx used in typical BEAM applications uses 4x more supply current than does 74HC/HCTxxx.
  •  
    The following material is intended to cover usage and part selection details of ICs you're most likely to see in BEAM robots.
York Jong

Robot Room - IRB and Roundabout Resourcess - 0 views

  • "Exposing a Flaw: Shoot-Through" describes the serious problem with that circuit, especially when pulsed
  • Above is an improved version of the circuit, which is now PWM compatible. PWM, coast mode, and the capability to avoid shoot-through are provided by adding a fifth MOSFET (labeled Q5) to the source/ground connections of Q1 and Q3.
  • ...1 more annotation...
  • By default at power-up, the circuit is in coast mode. To brake, set IN A to 0 V, IN B to 0 V, and Q5 to 5 V. To spin clockwise, set IN A to 5 V, IN B to 0 V, and Q5 to 5 V. To spin counterclockwise, set IN A to 0 V, IN B to 5 V, and Q5 to 5 V. At any time you can return to coast by applying 0 V to Q5. Or, you can apply pulses of 0 V/5 V/0 V/5 V (and so on) to control the speed. The more time spent at 5 V, the faster the motor will spin. Whenever you change modes, if you set Q5 to 0 V before making changes to IN A and IN B (and then set Q5 back to 5 V or pulsing) there will be no shoot-through.
  •  
    This secret page is for owners of the book, Intermediate Robot Building. On this page, you'll find updates, corrections, and source files. Thank you for buying the book!
1 - 4 of 4
Showing 20 items per page