Boe-Bot servos turn at different speeds and BothServosThreeSeconds fails withou

Steve_SSteve_S Posts: 3
edited 2004-08-25 - 19:56:06 in Robotics
I am assembling my boe-bot and as part of the servo test it has me center the servos and then test them in varous ways.· I notice the speeds were different, one slower, one faster on the two servors.

I also noticed that when I did the BothServosThreeSeconds.bs2 my system never reversed and never stopped.· So I had to add a "pause 10"·between the first and second loop (see code below).· Is this normal, or could my rechargable rayovac renewal's need help?· I have fully charged batteries in the battery pack.

counter VAR Byte
FOR counter = 1 TO 122
· PULSOUT 13, 850
· PULSOUT 12, 650
· PAUSE 20
NEXT
PAUSE 10
FOR counter = 1 TO 122
· PULSOUT 13, 650
· PULSOUT 12, 850
· PAUSE 20
NEXT

END

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2004-08-11 - 19:12:09
    Steve_S said...
    I am assembling my boe-bot and as part of the servo test it has me center the servos and then test them in varous ways.· I notice the speeds were different, one slower, one faster on the two servors.

    I also noticed that when I did the BothServosThreeSeconds.bs2 my system never reversed and never stopped.· So I had to add a "pause 10"·between the first and second loop (see code below).· Is this normal, or could my rechargable rayovac renewal's need help?· I have fully charged batteries in the battery pack.
    Steve, didn't really look at your code, but got as far as rechargable batteries and decided to mention, many of these types of batteries run at 1.2 or 1.3 volts, instead of the 1.5 volts that a typical battery runs at.· This can adversely affect your servo operations...


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    Chris Savage

    Knight Designs
    324 West Main Street
    P.O. Box 97
    Montour Falls, NY 14865
    (607) 535-6777

    Business Page:·· http://www.knightdesigns.com
    Personal Page:··· http://www.lightlink.com/dream/chris
    ·
  • Steve_SSteve_S Posts: 3
    edited 2004-08-11 - 19:43:12
    Chris,
    Thanks, my battery pack is at 5.3 w/o the servos running, and w/servos running it drops to 4.59, then when both servos switch it taks a transient sometimes as low as 3.8v on the battery pack. Time to renew my source [noparse]:)[/noparse].

    thanks,
  • Steve_SSteve_S Posts: 3
    edited 2004-08-11 - 19:48:14
    I found a bad battery in the bunch and the program works fine now without the pause. I guess this is now my bad battery detector program.

    Steve Stierwalt
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2004-08-11 - 19:54:16
    Steve_S said...
    I found a bad battery in the bunch and the program works fine now without the pause. I guess this is now my bad battery detector program.
    Steve Stierwalt
    Steve,

    ·· That's great...Still, if the batteries aren't rated at 1.5 volts each, I would still replace them with standard batteries.· Just my opinion.
    smilewinkgrin.gif


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    Chris Savage

    Knight Designs
    324 West Main Street
    P.O. Box 97
    Montour Falls, NY 14865
    (607) 535-6777

    Business Page:·· http://www.knightdesigns.com
    Personal Page:··· http://www.lightlink.com/dream/chris
    ·
  • Aristides AlvarezAristides Alvarez Posts: 470
    edited 2004-08-11 - 20:19:08
    Hello Steve.

    As Chris recommended, you have to source 6 Volts, preferably 4 AA alkaline (brand new) batteries.

    If you use lower voltage rechargeable ones, you'll have to use 5 batteries (not supported by the standard battery pack).

    If you have the Robotics V2.0 manual I can recommend you to check "ACTIVITY #3: Connecting the Servo Motors".
    Depending on the hardware you have (Board of Education or HomeWork Board) you'll find recommendations about settings/jumpers and even about batteries.

    There is a box on Page 57 (Robotics 2.0) that says:
    "Use only alkaline batteries. Avoid rechargeable batteries because they're 1.2 V instead of 1.5 V."

    You'll also find recommendations in how to set the servo power jumper in your Board of Education.

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    Saludos,
    Aristides Alvarez
    Education Manager
    aalvarez@parallax.com
    Parallax, Inc. www.parallax.com
    California, USA
  • Wade SmithWade Smith Posts: 25
    edited 2004-08-16 - 22:01:50
    Along the same voltage lines, though I threw 4 rechargeables in my Boe-Bot the other day and didn't get any brownout problems, is there any reason not to use a rechargeable nine volt (or two in parallel for more amps) on Bots like the Boe-bot or the Parallax Sumo-bot? The boards can handle nine volts and the rechargeables are I think 8.2 or something. Any thoughts on this? They are much more compact then 4 or 6 AAs.
  • Aristides AlvarezAristides Alvarez Posts: 470
    edited 2004-08-23 - 07:03:28
    Hello Wade.

    I can think about two considerations:
    1-Current/power capability of the rechargable battery you're going to use.
    Voltage is one of the variables when talking about batteries.
    Current is also another rating that when running motors or any high consumption load is important to take into account, not only to estimate battery or charge life but also brownout conditions.
    If your rechargable 9 Volt battery (or two in parallel) can provide enough current for both servomotors and the rest of the circuit, you should be able to use it/them.

    2-VERY IMPORTANT!
    We didn't test our Parallax Continuous rotation servos with more than 7 Volts (Parallax standard servos work fine with more than that).
    For this reason, if you decide to use 9 Volt rechargable batteries, you should move the servo-port power jumper to Vdd, in your Board of Education (Rev C.).

    This means that even though your battery will be 9 V (or close) the servos would be supplied with regulated 5 Volts.

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    Saludos,
    Aristides Alvarez
    Education Manager
    aalvarez@parallax.com
    Parallax, Inc. www.parallax.com
    California, USA
  • Wade SmithWade Smith Posts: 25
    edited 2004-08-23 - 16:14:50
    Hello Aristides,

    Thanks for the information. After my post I started comparing mA hours and like you say if you are running motors even two 9 volt batteries are not much compared to 4 or 6 AA for current. I know most servos can handle 8 volts but I appreciate the warning!

    Regards,

    Wade.
  • WorapohtWorapoht Posts: 17
    edited 2004-08-23 - 19:31:00
    if Servo had modified correctly.. cause of mistake action may come from power supply

    as I ever did, use BOE supply to 6xAA battery holder for long time to run BS2.
    and changed on-board voltage regulator IC to low dropout type (LM2940-5.0)

    as you may know, BS2 have brownout detection and reset if Vdd lower than 4.2V. that why program still do that.

    I'd recommended Servo motor supply should not exceed than 6 V. and jumbo coupling capacitor 4700uF apply to +Vmotor, to keep supply stable and reduce unwanted motor action..

    and "pause 10" command is too small to see changed because Servo need 20ms trail pulse signal before take motor action.
  • Aristides AlvarezAristides Alvarez Posts: 470
    edited 2004-08-25 - 19:56:06
    Hello Worapoht.

    It seems that you were Parallax customer for a long time, based in the hardware upgrades you mentioned in your message. [noparse]:)[/noparse]

    The latest servos we provide were pre-modified at factory (Futaba).
    The calibration process now is pretty simple, because the servo has a hole in the case that allows you to calibrate the central position of the servo without having to remove the case.
    They also have an internal capacitor and they run so smoothly that the voltage is pretty stable, so most of the times you won't need to use extra capacitors.

    The pause between pulses varies widely and usually it's in the range of 10 to 40 milliseconds.
    We usually use 20 milliseconds pauses, but if your program is checking sensors or doing some processing in between pulses you may want to decrease the value on the PAUSE command to avoid servo jittering.

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    Saludos,
    Aristides Alvarez
    Education Manager
    aalvarez@parallax.com
    Parallax, Inc. www.parallax.com
    California, USA
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