Alt-BEAM Archive
Message #07388
To: beam@sgiblab.sgi.com
From: Senior kyled@cruzers.com
Date: Fri, 05 Nov 1999 08:58:17 -0700
Subject: [alt-beam] Re: Cleaner Robots
What an awesome idea! I thought that would be the answer... WE'RE not
programmed :)
Kyle
Victor Snesarev wrote:
>
> Senior wrote:
>
> > Jason Chang wrote:
> >
> > > Hi all :)
> > >
> > > I've been trying to build some robots to clean up my room, and for this,
> > > I'm using recycled RC cars. the control circuits are fine, basically i'm
> > > using 2 head circuits back to back,(one head for left control, another for
> > > right control) and it follows a preset path of IR beacons. The whole bot
> > > works fine on the whole, but i realised something. the power supply to the
> > > bot may not be sufficient. :P Any Ideas on a suitable power source?
> > >
> > > I've thought of placing some recharging stations all around. But would that
> > > mean that the robots would not seek out the IR Beacons but the power
> > > source instead?
> > > any ideas on how to overcome this?
> >
> > Hey Jason! :)
> > Well, do they need to follow a preset path? Cuz I'm making a vacuum bot
> > for my tile kitchen (A real vacuum mind you! :) and I decided that if I
> > just had it kinda go randomly around than in the five hours it cleans it
> > must get prety much everywhere.
>
> [snip]
>
> A professor that's in charge of a robotics class here at University of Florida
> was telling his microprocessor apps. class how they've conducted an experiment
> with a cleaner-type robot. They put an LED on top of it, and let it run overnight
> in a room with some commonplace obstacles while having a camera with an open
> shutter sitting on the ceiling all night. So, a robot with some kind of preset
> pattern programmed into it did worst in covering the room than a robot that just
> had random response to obstacle avoidance.
>
> Cheers
>
> Victor
7389 Fri, 05 Nov 1999 12:04:46 -0600 [alt-beam] Re: PS HEAD V2 beam@sgiblab.sgi.com Brad Guillot for every one on the ps head project,
i was digging and found this in the archives
it doesn't have the circuitry for the fled,
but it has a very indepht description of the operation of the circuit.
it helped me understand the operation of the circuit alot better
later
brad
Wilf Rigter wrote:
>
> Prodded by Justin, here is an updated and tested version of the Power_Smart
> head circuit complete with a description of operation.
>
> The Power_Smart Head V2 - 9/99 - wilf rigter
>
> NOT A BICORE
>
> The basic BEAM head is a tried and proven design with a substantial number
> of working units posted at various websites. However the conventional bicore
> head circuit is difficult to adjust to operate over a wide range of light
> conditions and is notorious for high power consumption. The switching losses
> are significant, because the bicore is continually reversing the motor
> current. In fact, current required for a motor in a bicore head is almost
> double that needed with the motor connected straight to the power supply.
> Moreover the circuit consumes power even when the head is locked on and not
> moving.
>
> HIGH/LOW/OSCILLATE
>
> The Power_Smart (PS) head , as the name implies, was designed to address
> these problems while maintaining the same simple "freeformable" circuit
> layout and similar components. The PS circuit uses what could be called a
> modified bicore oscillator but which I will call the High/Low/Oscillator
> (HLO). This is in fact a textbook CMOS oscillator with a voltage
> controlled Pulse Width Modulation input. This PWM control input is simply a
> 1M resistor connected on one side to a voltage source (in this case the
> midpoint of two photo sensors ) and connected on the other side to bias
> point of the oscillator timing components (U1-pin2). Two photo sensors use
> reasonably well matched photodiodes or light depended resistors to form a
> voltage divider (or half bridge), with the voltage at the midpoint close to
> 1/2 Vcc when the light on each sensor is balanced. This 1/2 Vcc voltage is
> near the input switching threshold of standard 74HC240 (not HCT) logic. The
> control range was designed so that when the photo sensors are balanced,
> the oscillator produces a square wave with 50% duty cycle. When unbalanced,
> the duty cycle changes between 0% or 100% (full reverse to full forward).
> The two complementary outputs of the HLO are connected to the inputs of a
> bipolar pulse generator.
>
> A CHANGE OF PHASE
>
> The HLO is followed by the Nv/Nu (2N1) bipolar pulse generator. The 2N1 uses
> two capacitors and one resistor. The produces positive going AND negative
> going pulses with a pulsewidth about half the period of the HLO output. For
> the duration of the pulse width the output of the 2N1 is in phase with the
> resistor signal. If that signal is longer than the pulse width, the 2N1
> output changes to the inverse of the resistor signal. Since the resistor
> input signal and the 2N1 output are connected through a driver stage to the
> motor, it is the difference (out of phase) between these two signals which
> cause the motor current and rotation. Therefore a steady state signal
> applied to the 2N1 resistor input, when the sensor bridge is greatly
> unbalanced, will cause continuous rotation. When the sensor bridge is
> balanced and HLO oscillator produces a 50% duty cycle (squarewave), there
> is no difference signal developed between the 2N1 input and output and the
> motor does not rotate. When a HLO output is a pulse width modulated
> oscillation, the 2N1 circuit produces a pulse train phaseshifted with
> respect to the input signal with a pulse width difference which is
> proportional to the sensor bridge imbalance. This difference signal is a PWM
> signal the causes slow rotation of the motor when the sensor bridge is
> slightly unbalanced.
>
> TWO NEURONS IN ONE
>
> The Nv/Nu (2N1) circuit in one sense combines the functions of both types
> of neurons. Normally a Nu integrates a signal applied to the resistor with
> the capacitor grounded. A Nv differentiates a signal applied to the
> capacitor with the resistor grounded. The Nv/Nu stage applies signals to
> both the capacitor and the resistor. A second capacitor and second inverter
> is used to provide positive feedback to overcome the common problem of
> linear inverter high frequency oscillation as a Nu input voltage passes
> through the linear region. The driving outputs also act as virtual grounds
> for the respective capacitor and resistor. (note that the earlier power
> smart head used just one 240 stage for the Nv/Nu neuron resulting in bursts
> of high frequency oscillations especially when using the preferred 74AC
> logic) .
>
> HUNTING/SEEKING/TRACKING
>
> When there is a strong light source off-center from the photo sensor's line
> of sight, the midpoint of the sensor bridge is strongly unbalanced. This
> causes the PWM control input to saturate (full forward or reverse) and the
> oscillator output no longer pulses but stays high or low depending if the
> control voltage is higher or lower than the linear region. In this saturated
> state, the motor is driven continuously left or right, turning the photo
> sensors towards the light source . This provides a feedback servo loop
> driving the motor to balance the light level on the sensors until the
> control voltage is restored to 1/2Vcc. While the oscillator is saturated,
> all power is continuously (efficiently) applied to the motor without the
> switching losses common in Bicore designs.
>
> BUFFERIN/BUFFEROUT
>
> The output of the HLO and the Nv/Nu stages are buffered with 2 parallel
> inverters each and these can directly drive a small gear motor of the BG
> Micro type. If more power is needed then I recommend using a complementary
> mosfet h-bridge to source and sink up to 1A with low losses. With a heavy
> duty motor and the more powerful mosfet h-bridge, a PS head can be used to
> position a camera or other device (ie an electromagnetic BB gun : you'll
> shoot your eye out!).
>
> ONE MORE TIME
>
> To recap, the HLO generates a High or a Low output when the photo sensor
> bridge is unbalanced and Oscillates when each photo sensor receives roughly
> the same light. The complimentary outputs of the HLO connect to the inputs
> of a Nv/Nu stage which generates pulses when the HLO oscillates. The motor
> driver consists of a buffered bridge connected to one HLO output and the
> Nv/Nu output. The bridge drives the motor in one direction or the other when
> the photo sensors are unbalanced. When the photo sensors are slightly
> unbalanced, the motor driver produces narrow pulses (reduced power) to nudge
> the head position towards the balanced condition. When both photo sensors
> are equally illuminated, the HLO oscillates width 50% dutycycle square wave
> output. At this frequency and duty cycle, the Nv/Nu stage generates pulses
> which are precisely in phase with the HLO output. Therefore the bridge
> outputs are the same polarity, the motor is stopped and the brake is on.
> This is a low power standby mode which requires just 1 ma of supply current.
>
> 240 or not 240
>
> Since only 6 inverters are needed for the PS head, it is also possible to
> make a PS head using only one 74HC04 chip and MOSFET h-bridge or for small
> motors, use just a single 74AC04 chip. For a 2DOF PS head just duplicate the
> circuit and add another motor.
>
> AN EYE FOR AN EYE
>
> I recommend installing red and green LEDs connected in reverse parallel
> across the motor to indicate direction of motor rotation providing visual
> feedback.
>
> X MARKS THE SPOT
>
> Although not shown in the schematic, an auxiliary IR LED can be mounted on
> the head to provide an active IR SPOTLIGHT. The LED current can be also be
> synchronously Pulse Width Modulated to increase IR brightness while
> reducing overall power consumption. When using the IR SPOT, make sure the
> head is far from reflective walls, etc since the head will lock on any
> nearby object reflecting the IR beam.
>
> That's it for now: but remember feedback is always welcome here.
>
> enjoy
>
> wilf
>
> <>
>
> Wilf Rigter mailto:wilf.rigter@powertech.bc.ca
> tel: (604)590-7493
> fax: (604)590-3411
>
> ------------------------------------------------------------------------
> Name: SM_HEAD2.gif
> SM_HEAD2.gif Type: GIF Image (image/gif)
> Encoding: base64
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7390 Fri, 5 Nov 1999 13:31:05 -0600 [alt-beam] (OT) can't surf my own pond "cbrenizer" anybody have a sec to check my page. the isp guys say they can pull it up
but i can't. i get http error 404, file not found. i can get their page,
yahoo, etc... just not my own.
www.trib.net/~cbrenizer
should only be a single link and nothing else on the page, no graphics or
text....(i know, kind of a sad homepage but i that's not the point.) so you
don't have to go into the site. just let me know if you do or don't get the
error, off list. thanks!
i don't think my isp will believe me unless i get further proof that i'm not
being stupid....of course that leaves me wide open if no one else has
trouble doing it...
Þ-:
opcodejoe@mail.trib.net
ICQ# 11118760
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