## RE: [rsa] Re: Help Needed! Chips are in, but 1 questions still

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• Thank you again! Just got the chips in and am going to play with it today. Just one thing I am not clear on - putting a cap _across_ the motor leads. I
Message 1 of 16 , May 3 10:24 AM
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Thank you again! Just got the chips in and am going to play with it today.

Just one thing I am not clear on -
putting a cap _across_ the motor leads.
I understand from one current direction it will help ground out noise (reverse EMF?) or cut out AC frequencies, but as I am going to be using this motor in both directions and polarities, isn't that going to just create a parallel loop with the motor in one of the directions/polarities and cause problems?

and from both the leads to ground will do the same(creat a closed circuit in one direction), correct? So the motor would just be a resistive loop attached in parallel to a close circuit?

Sorry for what may seem a simple (dumb) question, but from what I know capacitors are basically a 1 way flow control valve in DC circuits, and a variable frequency cut off depending on the capacitors rating.

_____________________

Terry Kremin, Ph.D.
Postdoctoral Fellow
Ernest Gallo Clinic and Research Center, UCSF

*******************
"If the misery of the poor be caused not by the laws of nature, but by our institutions, great is our sin."      -- Charles Darwin

From: sfrsa@yahoogroups.com [mailto:sfrsa@yahoogroups.com] On Behalf Of rtstofer
Sent: Sunday, April 24, 2005 5:52 PM
To: sfrsa@yahoogroups.com
Subject: [rsa] Re: Help Needed! Not sure relays will work.

Ok, there are other considerations...

Try the 754410 driver chip.  It is good for about 800 mA per side at
a motor supply voltage of as low as 4.5V.  By the time you account
for losses through the chip, your 3V motor will probably be just
fine.

Now, each chip has 2 drivers so you can parallel them by simply
wiring similar functions in parallel - that ought to handle your
motor.

Here is a datasheet on the chip
http://www.acroname.com/robotics/parts/R6-754410.pdf

You can get heatsinks here:
http://www.kronosrobotics.com/xcart/customer/product.php?
productid=16248&cat=293&page=1

You can breadboard it on just about anything.  I tend to use a lot
of Radio Shack 276-168 boards - search by number at
www.radioshack.com but most stores stock them.

You will also need to put an inverter on the mercury switches - it
might as well include Schmitt triggering so the 74LS14 should work.
If you look at the driver truth table you will see that to run one
direction, 1A should be high while 2A should be low.  The opposite
polarity (1A low, 2A high) runs the motor the other direction.  So
run each mercury switch into an inverter to clean it up and run one
output to 1A and the other to 2A - ground the other 4 inverter
inputs (or use them for something else).  Tie the enable pins high
or, perhaps, switch them for overall control.  Ordinarily, the pulse
width modulated speed signal is injected on the enable pin.  You can
get a nice logic high from the output of one of those grounded
inverters.

There is no problem when both switches are in the same position - it
will apply braking to the motor.

If the braking is a problem, you will need to change the logic ahead
of the 1A and 2A inputs - post back.

One of the nice things about the 754410 is the kick-back diodes are
internal.  You should still put 0.1 ufd capacitors between each
motor lead (at the motor) and ground and ground the motor housing.
Also, put a 0.1 ufd capacitor across the motor leads.  This will

SF robot meetings are at 7PM on the first Wednesday of the month at SFSU's Science bldg - 1600 Holloway, room SCI 256.

http://www.robotics-society.org/images/sfsu_map.gif

• Hi Terry, ... I think you may be confusing diodes and capacitors. Diodes only allow current to flow in one direction. Some capacitors will only work properly
Message 2 of 16 , May 3 10:43 AM
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Hi Terry,

> Sorry for what may seem a simple (dumb) question,
> but from what I know capacitors are basically a 1
> way flow control valve in DC circuits, and a
> variable frequency cut off depending on the
> capacitors rating.

I think you may be confusing diodes and capacitors. Diodes only allow current
to flow in one direction.

Some capacitors will only work properly if they're connected with the correct
polarity (electrolytics and tantalums). The capacitors that you connect
across the motor are normally monolithic or ceramic, and these types of
capacitors work equally well with either polarity.

A capacitor is basically like a little storage device that can hold charge.
In the case of the motor, it absorbs the charge which is created by a current
spike, which is noise.

If you're familiar with modern plumbing, there's a device called a water
hammer arrestor they often put on your water lines before going to a washing
machine. These are basically performing the same function as a capacitor on
the motor. When the washing machine opens the valve quickly there is a sudden
inrush of water. The water hammer arrestor absorbs the initial shock. The
capacitor on the motor is doing the same thing when the PWM is switching on
and off.

metal case to each motor lead helps as well. The metal case will absorb the
RF trasnmitted by the brushes arcing, and the capacitors will allow it to be
dissapated.

--
Dave Hylands
http://www.DaveHylands.com/

-----Original Message-----
From: sfrsa@yahoogroups.com [mailto:sfrsa@yahoogroups.com] On Behalf Of Terry
Kremin
Sent: Tuesday, May 03, 2005 10:25 AM
To: sfrsa@yahoogroups.com
Subject: RE: [rsa] Re: Help Needed! Chips are in, but 1 questions still

Thank you again! Just got the chips in and am going to play with it today.

Just one thing I am not clear on -
putting a cap _across_ the motor leads.
I understand from one current direction it will help ground out noise
(reverse EMF?) or cut out AC frequencies, but as I am going to be using this
motor in both directions and polarities, isn't that going to just create a
parallel loop with the motor in one of the directions/polarities and cause
problems?

and from both the leads to ground will do the same(creat a closed circuit in
one direction), correct? So the motor would just be a resistive loop attached
in parallel to a close circuit?

_____________________
Terry Kremin, Ph.D.
Postdoctoral Fellow
Ernest Gallo Clinic and Research Center, UCSF
*******************
"If the misery of the poor be caused not by the laws of nature, but by our
institutions, great is our sin." -- Charles Darwin
• yep, you are completely correct, that is definitely it!! sorry about that. I had looked at trying to put diodes in my first homemade design, and my thought
Message 3 of 16 , May 3 11:17 AM
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yep, you are completely correct, that is definitely it!! sorry about that. I had looked at trying to put diodes in my first homemade design, and my thought process and logic got stuck there and I changed what I was calling them without actually changing them in my mental schematic!

I feel really dumb right now! Too many things and not enough bandwidth....

Thanks again for the help, and especially the rapidity of your help and suggestions - If I get any data from this rig published I will definitely give you a plug in the acknowledgements!

_____________________

Terry Kremin, Ph.D.
Postdoctoral Fellow
Ernest Gallo Clinic and Research Center, UCSF

*******************
"If the misery of the poor be caused not by the laws of nature, but by our institutions, great is our sin."      -- Charles Darwin

From: sfrsa@yahoogroups.com [mailto:sfrsa@yahoogroups.com] On Behalf Of Dave Hylands
Sent: Tuesday, May 03, 2005 9:43 AM
To: sfrsa@yahoogroups.com
Subject: RE: [rsa] Re: Help Needed! Chips are in, but 1 questions still

Hi Terry,

> Sorry for what may seem a simple (dumb)
question,
> but from what I know capacitors are basically a 1
>
way flow control valve in DC circuits, and a
> variable frequency cut off
depending on the
> capacitors rating.

I think you may be confusing diodes and capacitors. Diodes only allow current
to flow in one direction.

Some capacitors will only work properly if they're connected with the correct
polarity (electrolytics and tantalums). The capacitors that you connect
across the motor are normally monolithic or ceramic, and these types of
capacitors work equally well with either polarity.

A capacitor is basically like a little storage device that can hold charge.
In the case of the motor, it absorbs the charge which is created by a current
spike, which is noise.

If you're familiar with modern plumbing, there's a device called a water
hammer arrestor they often put on your water lines before going to a washing
machine. These are basically performing the same function as a capacitor on
the motor. When the washing machine opens the valve quickly there is a sudden
inrush of water. The water hammer arrestor absorbs the initial shock. The
capacitor on the motor is doing the same thing when the PWM is switching on
and off.

metal case to each motor lead helps as well. The metal case will absorb the
RF trasnmitted by the brushes arcing, and the capacitors will allow it to be
dissapated.

--
Dave Hylands
http://www.DaveHylands.com/

-----Original Message-----
From: sfrsa@yahoogroups.com [mailto:sfrsa@yahoogroups.com] On Behalf Of Terry
Kremin
Sent: Tuesday, May 03, 2005 10:25 AM
To: sfrsa@yahoogroups.com
Subject: RE: [rsa] Re: Help Needed! Chips are in, but 1 questions still

Thank you again! Just got the chips in and am going to play with it today.

Just one thing I am not clear on -
putting a cap _across_ the motor leads.
I understand from one current direction it will help ground out noise
(reverse EMF?) or cut out AC frequencies, but as I am going to be using this
motor in both directions and polarities, isn't that going to just create a
parallel loop with the motor in one of the directions/polarities and cause
problems?

and from both the leads to ground will do the same(creat a closed circuit in
one direction), correct? So the motor would just be a resistive loop attached
in parallel to a close circuit?

_____________________
Terry Kremin, Ph.D.
Postdoctoral Fellow
Ernest Gallo Clinic and Research Center, UCSF
*******************
"If the misery of the poor be caused not by the laws of nature, but by our
institutions, great is our sin."      -- Charles Darwin

SF robot meetings are at 7PM on the first Wednesday of the month at SFSU's Science bldg - 1600 Holloway, room SCI 256.

http://www.robotics-society.org/images/sfsu_map.gif

• Hey Everybody, I m new to robotics and I figured I d jump right in and help out a group that needs help with updating their robot. Right now, they control
Message 4 of 16 , Jun 20, 2005
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Hey Everybody,

I'm new to robotics and I figured I'd jump right in and help out
a group that needs help with updating their robot.

Right now, they control their robot's arms with R/C controllers,
but they would like to have it automated/autonymous.

So I want to use the BS2 to control the Vantec ESC RDFR.
Are there any website/info that show example on how to
program/wire the BS2 to send the proper PWM outs to
the Vantec?

Does anyone have any suggestions for a good shaft encoder to
obtain positioining data?

Cheers,
DK
• Hello DK, I recommend the BASIC book written by Edwards. He goes over many examples with sample code for the basic stamp. Also, www.parallax.com
Message 5 of 16 , Jun 20, 2005
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Hello DK,

I recommend the BASIC book written by Edwards.

He goes over many examples with sample code for the basic stamp.

Also, www.parallax.com has a forum in which you can post questions regarding the use of BS2, but if you purchase that book, you’ll probably not need to use the forums.

Cheers,

From: sfrsa@yahoogroups.com [mailto: sfrsa@yahoogroups.com ] On Behalf Of D K
Sent: Monday, June 20, 2005 8:48 PM
To: sfrsa@yahoogroups.com
Subject: [rsa] BS2, Vantec RDFR21, DC Motor ?

Hey Everybody,

I'm new to robotics and I figured I'd jump right in and help out
a group that needs help with updating their robot.

Right now, they control their robot's arms with R/C controllers,
but they would like to have it automated/autonymous.

So I want to use the BS2 to control the Vantec ESC RDFR.
Are there any website/ info that show example on how to
program/wire the BS2 to send the proper PWM outs to
the Vantec?

Does anyone have any suggestions for a good shaft encoder to
obtain positioining data?

Cheers,
DK

SF robot meetings are at 7PM on the first Wednesday of the month at SFSU's Science bldg - 1600 Holloway, room SCI 256.

• On Rusty I m driving two RC car ESC s (Novak XRS s) with a BS2 and Mini Serial Servo Controller (MSSC) . ESC s take
Message 6 of 16 , Jun 20, 2005
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On "Rusty" I'm driving two RC car ESC's (Novak XRS's) with a BS2 and Mini Serial Servo Controller (MSSC) <http://www.camppeavy.com/rusty.jpg>.

ESC's take commands just like servos. Have you used the Stamp to move a plain servo yet? If it works with a plain servo it should work with the ESC. ESC's just like servos are looking for pulses between 1 and 2 milliseconds (ms); 1-ms for one direction, 2-ms for the other and ~1.5-ms to stop. If you drive it directly from the BS2 you'll use the "pulsout" command. Pulsout 500 for one direction and 1000 for the other. The BS2's pulsout command runs at 2 micro-second (1/1,000,000/sec) units so 500 x 2 micro-seconds = 1 millisecond (1/1,000/sec) and 1000 x 2 micro-seconds = 2 milliseconds. The "stop" value should be 750 but it usually ranges between 730 and 770.

Once you get it going you might want to seriously consider off-loading the pulsing to a peripheral board like the MSSC otherwise your Stamp might be too busy to do anything else. With the MSSC your Stamp simply gives it a value between 0 and 254 and goes back to more important things. The peripheral board does the pulsing.

One of the tricks with the Novak XRS is you had to put it in the "stop" position before changing directions. They call this Smart Braking II. I implemented it through a gosub routine.

Good luck and keep us posted.

Camp

• Thanks Camp and Fredrick. I have run through the Stamp in Class tutorial with the BS2 to move a Servo. I just wasn t sure if that was the same approach.
Message 7 of 16 , Jun 21, 2005
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Thanks Camp and Fredrick.

I have run through the Stamp in Class tutorial with the BS2 to move a Servo.
I just wasn't sure if that was the same approach. Thanks for the info.
I'll try it out and let you guys know how it goes.

If anyone with robotics experience is interested in playing with and help
modifiying our
robot from R/C controlled to BS2 controlled please let me know and I will
give you more details. We are located in San Francisco.

At this time we are only looking for an experienced Robotics Volunteer.
I'm already the inexpereinced volunteer. :)

Cheers,
Dennis K.
• ... Does this robot have a particular function or is it free-range ? Camp
Message 8 of 16 , Jun 21, 2005
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> If anyone with robotics experience is interested in playing with and help modifiying our robot from R/C controlled to BS2 controlled please let me know and I will give you more details. We are located in San Francisco .

Does this robot have a particular function or is it "free-range"?

Camp

• Hi,Camp and Peavy, I want to get more details about your robot. But I don t know enough about it. Pls send to me the information as detailed as possible. ...
Message 9 of 16 , Jun 21, 2005
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Hi,Camp and Peavy, I want to get more details about your robot. But I don't know enough about it. Pls send to me the information as detailed as possible.

----- Original Message -----
Sent: Wednesday, June 22, 2005 1:21 AM
Subject: Re: [rsa] BS2, Vantec RDFR21, DC Motor ?

> If anyone with robotics experience is interested in playing with and help modifiying our robot from R/C controlled to BS2 controlled please let me know and I will give you more details. We are located in San Francisco .

Does this robot have a particular function or is it "free-range"?

Camp

SF robot meetings are at 7PM on the first Wednesday of the month at SFSU's Science bldg - 1600 Holloway, room SCI 256.

http://www.robotics-society.org/images/sfsu_map.gif

• Try www.humball.com They ve a good integrated, software upgradeable controller. Z.M ... From: sfrsa@yahoogroups.com [mailto:sfrsa@yahoogroups.com] On Behalf Of
Message 10 of 16 , Jun 21, 2005
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Message
Try www.humball.com
They've a good integrated, software upgradeable controller.
Z.M
-----Original Message-----
From: sfrsa@yahoogroups.com [mailto:sfrsa@yahoogroups.com] On Behalf Of D K
Sent: Monday, June 20, 2005 8:48 PM
To: sfrsa@yahoogroups.com
Subject: [rsa] BS2, Vantec RDFR21, DC Motor ?

Hey Everybody,

I'm new to robotics and I figured I'd jump right in and help out
a group that needs help with updating their robot.

Right now, they control their robot's arms with R/C controllers,
but they would like to have it automated/autonymous.

So I want to use the BS2 to control the Vantec ESC RDFR.
Are there any website/info that show example on how to
program/wire the BS2 to send the proper PWM outs to
the Vantec?

Does anyone have any suggestions for a good shaft encoder to
obtain positioining data?

Cheers,
DK

SF robot meetings are at 7PM on the first Wednesday of the month at SFSU's Science bldg - 1600 Holloway, room SCI 256.

http://www.robotics-society.org/images/sfsu_map.gif

• Yummm... Free Range Robots... They re real good with mustard and onions. ... robot from R/C controlled to BS2 controlled please let me know and I will
Message 11 of 16 , Jun 22, 2005
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Yummm... Free Range Robots... They're real good with mustard and onions. <drool>

--- In sfrsa@yahoogroups.com, Camp Peavy <cpeavy2@y...> wrote:
>
> > If anyone with robotics experience is interested in playing with and help modifiying our
robot from R/C controlled to BS2 controlled please let me know and I will give you more
details. We are located in San Francisco.
>
>
>
> Does this robot have a particular function or is it "free-range"?
>
>
>
> Camp
• ... ... more like motors and Ohmions . ;-) - cp
Message 12 of 16 , Jun 22, 2005
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> Yummm... Free Range Robots... They're real good with mustard and onions. <drool>
... more like motors and Ohmions <sorry!>. ;-) - cp

• So if a ESC takes commands like a servo, does the ESC also control a DC motor like a servo? More specifically will it control the DC motor output to a given
Message 13 of 16 , Jun 27, 2005
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So if a ESC takes commands like a servo, does the ESC also control a DC
motor like a servo?
More specifically will it control the DC motor output to a given position
based on the PWM,
just as a servo would be commmanded to a given position based on the PWM?

Or would it need feedback from an encoder to determine position?

How do i control the speed of the motors using the ESC if i am only sending
Stop (1.5ms), CCW (1 ms) and CW (2ms) PWM commands?

Thanks everyone for helping me with my newbie questions.

DK

----Original Message Follows----
From: Camp Peavy <cpeavy2@...>
To: sfrsa@yahoogroups.com
Subject: Re: [rsa] BS2, Vantec RDFR21, DC Motor ?
Date: Mon, 20 Jun 2005 23:27:14 -0700 (PDT)

On "Rusty" I'm driving two RC car ESC's (Novak XRS's) with a BS2 and Mini
Serial Servo Controller (MSSC) <http://www.camppeavy.com/rusty.jpg>.

ESC's take commands just like servos. Have you used the Stamp to move a
plain servo yet? If it works with a plain servo it should work with the ESC.
ESC's just like servos are looking for pulses between 1 and 2 milliseconds
(ms); 1-ms for one direction, 2-ms for the other and ~1.5-ms to stop. If you
drive it directly from the BS2 you'll use the "pulsout" command. Pulsout 500
for one direction and 1000 for the other. The BS2's pulsout command runs at
2 micro-second (1/1,000,000/sec) units so 500 x 2 micro-seconds = 1
millisecond (1/1,000/sec) and 1000 x 2 micro-seconds = 2 milliseconds. The
"stop" value should be 750 but it usually ranges between 730 and 770.

Once you get it going you might want to seriously consider off-loading the
pulsing to a peripheral board like the MSSC otherwise your Stamp might be
too busy to do anything else. With the MSSC your Stamp simply gives it a
value between 0 and 254 and goes back to more important things. The
peripheral board does the pulsing.

One of the tricks with the Novak XRS is you had to put it in the "stop"
position before changing directions. They call this �Smart Braking II�. I
implemented it through a �gosub� routine.

Good luck and keep us posted.

Camp
• ... The ESC will not hold position like a servo you probably want a stepper motor. I ve got this one http://www.parallax.com/detail.asp?product_id=27964 but
Message 14 of 16 , Jun 27, 2005
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> So if a ESC takes commands like a servo, does the ESC also control a DC motor like a servo?

The ESC will not hold position like a servo you probably want a stepper motor. I've got this one http://www.parallax.com/detail.asp?product_id=27964 but haven't done anything with it yet. I'll give it a go and give you some feedback <pun intended>.

Camp

• ... The Electronic Speed Controller is just that - a motor SPEED controller. You can vary the direction and speed of a motor by varying the pulse width of the
Message 15 of 16 , Jun 27, 2005
• 0 Attachment
Quoting D K <dktkd@...>:

> So if a ESC takes commands like a servo, does the ESC also control a DC
> motor like a servo?
> More specifically will it control the DC motor output to a given position
> based on the PWM,
> just as a servo would be commmanded to a given position based on the PWM?
>
> Or would it need feedback from an encoder to determine position?
>
> How do i control the speed of the motors using the ESC if i am only sending
> Stop (1.5ms), CCW (1 ms) and CW (2ms) PWM commands?
>
> Thanks everyone for helping me with my newbie questions.

The Electronic Speed Controller is just that - a motor SPEED controller. You
can vary the direction and speed of a motor by varying the pulse width of the
input (i.e. servo) signal. Therefore, 1ms would be full-speed in one
direction, and 2ms would be full-speed in the other direction. Anything in
between will translate to a lower speed, typically with 1.5ms being "off".

By the way, servos that have been modified for free rotation (i.e. to be used
to drive wheels) behave similarly, but don't require the added expense of an
ESC. But it's slower, since servos are geared down a lot. But if you're
looking to simply rotate something to a known position, I think a servo is the
simplest (and cheapest) way to go.

If you want to note wheel rotation on a free-wheeling motor or servo, you
would have to use some kind of encoder to determine rotational position. And
I'm sure there must be a discussion board somewhere devoted just to that
topic. ;)

Bill H.
• Thanks Camp and Bill. I didn t think it would be that easy but I figure I ask. If you were interested, the group that I am helping out is called Omnicircus.
Message 16 of 16 , Jun 27, 2005
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Thanks Camp and Bill.

I didn't think it would be that easy but I figure I ask.

If you were interested, the group that I am helping out
is called Omnicircus. Just do a search and you'll find them online.

Thanks again.
DK

----Original Message Follows----
From: Camp Peavy <cpeavy2@...>
To: sfrsa@yahoogroups.com
Subject: Re: [rsa] BS2, Vantec RDFR21, DC Motor ?
Date: Mon, 27 Jun 2005 13:16:21 -0700 (PDT)

> So if a ESC takes commands like a servo, does the ESC also control a DC
motor like a servo?

The ESC will not hold position like a servo you probably want a stepper
motor. I've got this one http://www.parallax.com/detail.asp?product_id=27964
but haven't done anything with it yet. I'll give it a go and give you some
feedback <pun intended>.

Camp
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