Subject:
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Re: More powerful motor (was: stuff)
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Newsgroups:
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lugnet.robotics
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Date:
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Thu, 28 Oct 1999 22:59:47 GMT
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Original-From:
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Stephen Unwin <stephen@elmsfarm.demon(StopSpam).co.uk>
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Viewed:
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637 times
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On Fri 15 Oct, Robert Ashford wrote:
> You need to be careful if you use more powerfull motors with lego construction. The p
> lastic parts are very strong but you can easyly break teeth off of the gears or twist
> the rods with the current motors and a little bit of gearing.
>
> On the other hand if you are going to build something out of other materials, you need
> to realize that the signal comming out of the RCX motor port is PWM (pulse width modu
> lated) the speed of the motor is controled by the frequency of pulses sent to the moto
> r. It may be possible to amplify the signal.
>
> Anyone know how to amplify a signal that can be positive or negative. Maybe an H-Brid
> ge would work. Any suggestions?
>
> Robert Ashford
On Sat 16 Oct, Stephen Unwin (Me) wrote:
> The following circuit should provide directional control
> of a DC motor using two SPDT (Single Pole Double Throw) relays
> and four diodes, but may not act quick enough for a PWM drive.
also there is short-circuit braking which will also come into play during PWM pulses
>
>
>
> .--------O---------------------------.
> | | |
> | | O-------------.
> | | | |
> | \----/ \----/ .-------.
> | \ / \ / |Relay 1|
> | __\/__ __\/__ '-------'
> O | | |
> | O-------------'
> RCX | |
> Output | |
> O-------------. |
> O | | |
> | --/\-- .-------. --/\--
> | / \ |Relay 2| / \
> | /----\ '-------' /----\
> | | | |
> | O-------------' |
> | | |
> '--------O---------------------------'
>
>
> V+
> |
> O-----------------.
> | |
> O| O|
> nc 1 | | nc 2
> O| O|
> | ___ |
> | .-/ \-. |
> O----| | M | |----O
> | '-\___/-' |
> | |
> O | O |
> no 1 | | no 2
> O | O |
> | |
> O-----------------'
> |
> GND
>
>
>
> I have just come back from the pub where I've been thinking about this.
> I haven't looked at the output signals on an oscilloscope yet, but I think
> the following may work.
> Assuming you are driving a more substantial motor than a LEGO one, you will
> have a separate power source with which to power any circuitry.
> You can have two op-amps set up as comparator circuits with a small (+0.5v)
> bias on the positive inputs. On one op-amp the +input gets one side of the
> RCX output and the -input gets the other side. This is reversed on the
> second op-amp. The output of one these comparators goes to SET of an S/R
> flip/flop and the other to the RESET.
Forget that! (it does work but it can be simplified).
Assuming a separate supply again for a more powerful motor, use a 5V voltage
regulator for logic power. Create two potential dividers with 10k resistors
to give 2.5v at the mid point. Connect the two wires from the RCX to these
two mid points and refer to them as A and B. Take both A and B into a NAND
gate (7400), this will give a PWM output signal. Also take the A signal into
the S of an SR latch (7474) and the B into the R input.
> This will give a logic signal for the
> direction on Q of the flip/flop and an inverse signal on Qbar.
> Both signals from the comparators can also be NANDed to give a logic pulse
> for PWM. These three signals can go into half of a L293D driver chip or
> a stepper motor driver chip.
> in1 = Q
> in2 =Qbar
> enable = NAND output.
This circuit seems to work on my test rig. How it may be affected by
noisier environments, I don't know.
I have a 6k GIF or 5k ACORN DrawFile schematic I can email if anyone is
interested.
/////
< .. >
>
- stephen@elmsfarm.demon.co.uk
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Message is in Reply To:
 | | Re: More powerful motor (was: stuff)
|
| You need to be careful if you use more powerfull motors with lego construction. The plastic parts are very strong but you can easyly break teeth off of the gears or twist the rods with the current motors and a little bit of gearing. On the other (...) (25 years ago, 15-Oct-99, to lugnet.robotics)
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