Alt-BEAM Archive
Message #06086
To: beam@sgiblab.sgi.com
From: "Jason -" evenflow88@hotmail.com
Date: Wed, 15 Sep 1999 10:11:09 GMT
Subject: [alt-beam] efficient gearmotors
I would really like to know why in a walker that uses servo need to have a
mechanical stop while a walker that uses a bgmicro gearmotors dont need
it...thanks....
______________________________________________________
6087 Wed, 15 Sep 1999 21:56:33 +0800 [alt-beam] 74XXX245 "Zulu"
Hello,
This is Zulu here,...sorry for bothering, but i have a question for you,
I just made and tested a Motor Driver using a 74hc245 chip and the results
are as follows..
(for one of the motors)
out of the 2 inputs, when one inputs is tied to 3 volts, the motor spins in
one direction. when the 3 volts are removed, the motor continues to spin
for a while. if the 3 volts is applied to the other input, the motor
stalls.
curious, i connected a 2 colour LED (red/Green) to both the motor outputs.
(the LED works this way : its has 3 leads, a ,b , and c. when a voltage is
applied to a and b, one colour (red) will appear. when the voltage is
applied to B and C, the other colour appears. thus, i connected A and C to
the outputs, while B went to gnd) when i repeated the test, i obtained this
result. the LED turns red when the output connected to A is enabled. then,
heres the funny part. when i enable the output to C and disabled the output
to A, the LED turned orange (both the red and Green portions of the LED
were turned on) for a period of time before changing to green.
both the drivers on the 245 acted the same way. is this normal, or is there
something that i'm missing here?
also, thanks for the help on the monocore head , Z bridge and on how to
convert images to *.gif formats... i owe you one.. :P
hope you can help .. :)
rdgs
Zulu
6088 Wed, 15 Sep 1999 07:31:42 -0700 [alt-beam] Re: 74XXX245 "'beam@sgiblab.sgi.com'" Wilf Rigter Probably a case of the floating input syndrome. Just attach 3.3M resistors
(or any other large value) between the inputs and ground. When you apply 3V,
the input will be at logic one and when you remove 3V the input will be at
logic zero instead of floating around in never never land.
Wilf Rigter mailto:wilf.rigter@powertech.bc.ca
> -----Original Message-----
> From: Zulu [SMTP:zulu35@singnet.com.sg]
> Sent: Wednesday, September 15, 1999 6:57 AM
> To: beam@sgiblab.sgi.com
> Subject: 74XXX245
>
>
> Hello,
>
> This is Zulu here,...sorry for bothering, but i have a question for you,
>
> I just made and tested a Motor Driver using a 74hc245 chip and the results
> are as follows..
>
> (for one of the motors)
> out of the 2 inputs, when one inputs is tied to 3 volts, the motor spins
> in
> one direction. when the 3 volts are removed, the motor continues to spin
> for a while. if the 3 volts is applied to the other input, the motor
> stalls.
>
> curious, i connected a 2 colour LED (red/Green) to both the motor outputs.
> (the LED works this way : its has 3 leads, a ,b , and c. when a voltage is
> applied to a and b, one colour (red) will appear. when the voltage is
> applied to B and C, the other colour appears. thus, i connected A and C to
> the outputs, while B went to gnd) when i repeated the test, i obtained
> this
> result. the LED turns red when the output connected to A is enabled. then,
> heres the funny part. when i enable the output to C and disabled the
> output
> to A, the LED turned orange (both the red and Green portions of the LED
> were turned on) for a period of time before changing to green.
>
> both the drivers on the 245 acted the same way. is this normal, or is
> there
> something that i'm missing here?
>
>
> also, thanks for the help on the monocore head , Z bridge and on how to
> convert images to *.gif formats... i owe you one.. :P
>
> hope you can help .. :)
>
> rdgs
> Zulu
6089 Wed, 15 Sep 1999 10:01:49 -0600 [alt-beam] Re: 74XXX245 beam@sgiblab.sgi.com Dave Hrynkiw At 07:56 AM 9/15/99 , Zulu wrote:
>out of the 2 inputs, when one inputs is tied to 3 volts, the motor spins in
>one direction. when the 3 volts are removed, the motor continues to spin
>for a while. if the 3 volts is applied to the other input, the motor
>stalls.
.
.
.
>then,
>heres the funny part. when i enable the output to C and disabled the output
>to A, the LED turned orange (both the red and Green portions of the LED
>were turned on) for a period of time before changing to green.
>
>both the drivers on the 245 acted the same way. is this normal, or is there
>something that i'm missing here?
It stems from the fact that you're only putting a logic signal to one of
the gates and leaving the other one "floating". Floating refers to not
having a definite "high" or "low" signal, allowing it to "float" between
the two without any definite state. WHen you power the 245 from
complimentary neurons on a microcore, one is DEFINITELY LOW or DEFINITELY
HIGH (ie: low=gnd, high=+3v) - no floating about it!
One way to fix this is with "pull up" or "pull down" resistors. Use around
1Meg connected to +3 or Gnd. Connected to +3V, it's a "Pull up" (pulling
the input up to +3), alternately, connected to gnd, it's a "pull down".
This puts a default logic condition to the gate.
Now, if you want to over-ride this condition, just use a resistance
substantially lower going to the other polarity. Ie: if the gate has a
pull-up resistor, and you want it now be low, use a 47k resistor connected
to ground to "pull it low". Or don't use a resistor at all. Since this will
make the gate "see" much more of a ground signal than the +3V it had with
the pull-up resistor, it'll change states, no questions about it!
There - hope that helped!
Regards,
Dave
---------------------------------------------------------------
"Um, no - that's H,R,Y,N,K,I,W. No, not K,I,U,U, K,I,_W_. Yes,
that's right. Yes, I know it looks like "HOCKYRINK." Yup, only
2 vowels. Pronounciation? _SMITH_".
http://www.solarbotics.com
6090 Wed, 15 Sep 1999 09:51:17 -0600 [alt-beam] Re: efficient gearmotors beam@sgiblab.sgi.com Dave Hrynkiw At 04:11 AM 9/15/99 , Jason - wrote:
>I would really like to know why in a walker that uses servo need to have a
>mechanical stop while a walker that uses a bgmicro gearmotors dont need
>it...thanks....
It all depends on the physical layout of the motors on the walker. You will
notice that many of Mark's walkers have stops arranged to hit the legs (ie:
Stryder), and many others don't (ie: Walkman).
In general, if you can expect gravity to help pull the motor leg into the
appropriate position, you don't need the stops. With Walkman, it's the
angle of the motor in respect to the horizontal surface that does this.
Same with many of his later "Unibug" walkers. With some, the front leg
motor is all lift (which gravity pulls the body back down - natural
assist), and the rear is all thrust, and requires stops and/or springs to
assist going back into neutral position).
Take a close look of the pics of Mark's bots - you'll see it.
BTW - sorry to all about the lack of web update. Be assured that I'm
working on it on a daily basis, and the totally new site will be up in a
week or two.
Regards,
Dave
---------------------------------------------------------------
"Um, no - that's H,R,Y,N,K,I,W. No, not K,I,U,U, K,I,_W_. Yes,
that's right. Yes, I know it looks like "HOCKYRINK." Yup, only
2 vowels. Pronounciation? _SMITH_".
http://www.solarbotics.com
6091 Wed, 15 Sep 1999 16:24:23 -0300 [alt-beam] Re: efficient gearmotors alt-beam@egroups.com michael.hirtle@ns.sympatico.ca (Michael Hirtle) Walker that use hacked servos don't need it but since the servos have a
mecanical stop they are stuck with it
Jason - wrote:
> I would really like to know why in a walker that uses servo need to have a
> mechanical stop while a walker that uses a bgmicro gearmotors dont need
> it...thanks....
>
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