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Self Charging Boe Bot — Parallax Forums

Self Charging Boe Bot

Ray IddingsRay Iddings Posts: 47
edited 2005-04-26 00:48 in Robotics
Is anyone working on this, or got it to work? I would love to see some examples because Im not sure how to attack this problem, reliably and simply.

Ray

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Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-04-03 01:37
    Ray,

    ·· Check out the "Robo-Cut" and the "OctoBot."· Both self-charging robots.· Both pretty popular.· You can find them via Google.



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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • voodoofishvoodoofish Posts: 67
    edited 2005-04-03 06:49
    I'm sure this is not what you meant, but I'm actually looking at putting the stuff I learn from "experiments with renewable energy" into a bot. I Know i'm getting ahead of myself, but I was looking at having a solar powered bot, that charges it's batteries during the day and uses the extra power to run it's normal opporations...whatever those end up being....I figure a dedicated stamp for that processing, one for doing experiments, central command sort of thing.

    Technically, this would be self charging·...·

    tongue.gif

    Ciao,
    Mark
  • GadgetmanGadgetman Posts: 2,436
    edited 2005-04-03 12:14
    Tough job..

    Small Solar panels doesn't deliver much power, I'm afraid.
    Just take a look at the Mars Rover and similar solar powered projects.

    Their entire top is covered in solar panels, of a better quality than you can expect to get hold of, the electronics is optimised for low-power, every mechanical component is made as light as possible...

    If you want to have any hope of getting any power at all, you'll need to have the panels tilted to follow the sun perfectly.
    If you really want to try, I suggest using a BS1 for this task as that's the Stamwh which draws the least power.

    You'll need to carefully consider the motors you use to position the panels.
    Do you want as small as possible, adding less weight and drawing less power , but is slower to adjust the panels, or
    do you want bigger motors which draws more power and can adjust the panels quickly?
    Will the bot be moving a lot?
    Will it be going mostly straight, or turning a lot?
    will it be operating on even ground, or bumpy roads?

    There's a lot of questions to consider, and no easy answers.
    (Of course, being Stampers, we don't DO the easy answers... smile.gif

    Hope I didn't scare you away...

    smile.gif
  • Ray IddingsRay Iddings Posts: 47
    edited 2005-04-03 14:06
    Im interested in leting the boebot roam around, monitior power, when it gets to a certian state it seeks out its charger and charges until its full, then it starts roving again. just not sure how to accomplish this, thinking outload and looking for input.

    Ray

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  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-04-03 18:11
    Ray,

    ·· Hence my previous reply...Both robots demonstrate that ability, and if you read up on them, perhaps you will get some ideas.

    ·· It seems the main thing is to be able to check your current power level of the batteries, and when they reach a certain threshold voltage, you need to start tracking a "beacon," which could be an IR LED.· This is something easy for a BOE-Bot to track and move toward.

    ·· Then you have the hurdle of a mechnical interlock which can easily charge the batteries while the BOE-Bot simply stops in front of it.· Both bots I mentioed above have accomplished this task quite effectively.· Good luck!


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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com


    Post Edited (Chris Savage (Parallax)) : 4/4/2005 1:31:20 AM GMT
  • GadgetmanGadgetman Posts: 2,436
    edited 2005-04-03 18:53
    If you're worried about exposed electrical connectors or making a positive lock, you may also consider an inductive power transfer.

    Pump low voltage AC current through a coil on the base, then move the bot close enough to pick it up with a coil built into the bot.
    Then it's just a question of feeding it through a rectifier and smooth it with a decent sized capacitor.
  • gelfling6gelfling6 Posts: 60
    edited 2005-04-03 21:08
    Gadgetman said...
    If you're worried about exposed electrical connectors or making a positive lock, you may also consider an inductive power transfer.

    Pump low voltage AC current through a coil on the base, then move the bot close enough to pick it up with a coil built into the bot.
    Then it's just a question of feeding it through a rectifier and smooth it with a decent sized capacitor.

    Hmm.. might raise havoc, putting a AC coil, under the servos, which both have perminant magnets in their drive motors.
    Exposed connections, Also a bad idea.. but, millions of cordless & cellular phones have them too.. nono.gif

    An alternative, would have to be some kind of targeting system, with a wide target. kind of like NASA uses for their
    manned space missions, where the docking platform has a circled "+", the astronauts need to line-up on, to insure
    a fit with the docking ports.

    Hmm.. Cordless phones... That just gave me a brainstorm.. I had a cordless phone, which had perminant
    magnets built into the contacts on the handset, and the pins on the charger/base were spring-loaded..

    Idea: magnets behind the contacts of the BOE, and opposite pole magnets on the charger base contacts.
    put the contacts for both inside some kind of shield, but leave just enough recess depth so the contacts will extend
    when the magnets on the opposite (charger/BOE) make contact, But not too strong, that it makes it impossible
    for the BOE to pull away (or pull the charger along with it. freaked.gif

    example (in awful typed graphics) Bot: =[noparse][[/noparse] ]= :charger (away from eachother)
    Bot: [noparse][[/noparse]==] :charger (when in contact)

    Now, the fun part, telling the BOE when it's had enough to eat, and back away.

    Stephen (gelfling6)
  • RsadeikaRsadeika Posts: 3,822
    edited 2005-04-03 22:14
    Another reason why I started looking into the SXxx chip. For my robot I will have to keep a close eye on when the batteries get low, and will have to start heading for the charger. In the SX book they describe a circuit, 'Detecting a low battery' using one pin and some resistors, its quite simple, when you look at the diagram. Implementing it is probably another story. I also looked into that when my robot was being controlled by a BS2. In the pbasic manual they have a diagram that shows how to posibly do what you are looking for. For me it was way to complicated, implementing pots and other things.
  • BeanBean Posts: 8,129
    edited 2005-04-03 22:37
    Also with the SX you can run it on the internal 32KHz clock. If you don't need much speed, the thing draws about 1.3mAmps at 5volts, if you run it from 3.3 or 2.7 the current will be even less.
    Bean.

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    www.sxvm.com

    "A problem well defined, is a problem·half solved."
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  • Ray IddingsRay Iddings Posts: 47
    edited 2005-04-04 03:45
    hmmm...Lets move away from the physical connection for a second (bot to charger) and focus on finding the charger for a second.

    lets say the bot reads the battery is low and goes from its autonomous roaming state to looking for food state. I wonder if I took the Tab Sumo Bot board and incorperated it into the charging station. Lets say the charging station becomes the beacon. Even if you couldn't get the boe to read its battery state maybe you could use the charging station as a clock say after the bot has left the station the charging stations waits, I don't know 45 minutes an hour then starts to flash a beacon for the bot. (like my Mom did when I was a kids, she'd turn on the porch light = time to come home)

    now the bot has to hone in on the charging station. But what to use as the beacon. Photorestiors would be to weak IMHO...

    I have a Tab Sumobot and a Boebot, I would like these to be the main componets of my little experment. I looked at the octabot and the robomower but they didn't really help.

    It would seem I need to 1) monitor battery state or use a predetermined roaming time
    2) find the charger
    3) charge till the battery is full or charge a predetermined time
    4) successfully leave the charge

    again Im still just think about how, and thinking out loud and since you guys have some of the biggest brains I thought I would start by thinking and talking about it before I started blowing things up. smile.gif

    or as my wife says " your project is making that smell, you know THAT smell!"

    FYI as I think about this more I wonder if the same principle as the Garage Sonic Range Parking Assistant http://forums.parallax.com/showthread.php?p=523373·, I wonder if the same principle could be applied, except the car would be the bot?

    Ray

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    Post Edited (Ray Iddings) : 4/4/2005 3:47:57 AM GMT
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-04-04 04:50
    Ray,

    ·· Phototransistors could work.· But the best way to get rid of ambient interference is to use a modulated signal.· To that end you could use an IR detector just like those included with the BOE-Bot to search for a modulated (38khz) IR signal.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • Paul BakerPaul Baker Posts: 6,351
    edited 2005-04-04 15:00
    There are a few ways of accomplishing the robot finding the food source, one way is to maintain a position log, the problem with this is that dirrectional errors will creep into you calculations. Or you can use an absolute position system, such as a GPS, where it knows the gps coordinates of its food bowl.

    The other major means is like what Chris mentioned, a homing beacon. This can be done either with RF or IR, but IR is cheaper and easier to manage by a stamp. The beacon would be several IR LEDs mounted axially like the spokes of a wheel and driven together. When the battery power drops it would switch from roam to seek, which is exactly the same as roaming except when it detects the beacon it uses that vector as its direction.

    There is a potential problem with the IR beacon and that is if you are using IR as your object avoidance system, the beacon can blind your robot. A method around this is to create an intelligent beacon. When your bot is just roaming it just uses the IR carrier and looks for the reflection. When it is in seek mode, it will send out a modulated IR signal that you predetermine. When your beacon detects this special modulated IR signal, it will echo back a response and your bot will know the direction to the food bowl.

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  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-04-04 15:58
    Paul,

    ·· The only potential problem I can forsee with the Beacon being activated, is that the BOT would have to spin around several times sending out it's activation signal, while monitoring the see if this has occurred.· Not that big of a deal, but for some it might make things too complicated.

    ·· Another method might be to use a lower frequency modulation for the IR beacon altogether.· This would involve using a different receiver, but still pretty easy.· And finally, a radio signal could be emitted from the BOT to activate the IR Beacon...If it's not found within a few rotations, the BOT could re-transmit.

    ·· All are valid courses of action, and I guess the complexity is a matter of perspective.· I guess the best we can do is offer suggestions, and the OP can use one, some, all or none!· smilewinkgrin.gif

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • Ray IddingsRay Iddings Posts: 47
    edited 2005-04-04 16:10
    LOL, I appreciate all the ideas (If I have one of my kids plug it in when it gets low does that count as self charging..hehe). The more solutions I think about the more issue I add to the list. For example, If you use the IR for obstacle avoidance then override it to home in on the charging beacon, you lose obstacle avoidance which you still may need to navigate to the charging station...This is going to be fun (I mean that). this problam is about 6" over my head, which I like.


    Tonight I will set up a Homebase and see if I can start to get the bot there, baby steps...I just thought when I asked this question someone else might have already blazed a trail.

    Black is ground right??

    Thanks

    Ray

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  • Paul BakerPaul Baker Posts: 6,351
    edited 2005-04-04 16:22
    A slight clarification, when in seeking mode, you wouldn't loose your IR avoidance system. You would continue to use unmodulated 38kHz for object avoidance, but you would inject a modulated code inbetween object avoidance cycles and look for a becon response (perferable the reply code would be a different code so your bot doesn't misinterpret a reflected code as being the becon).

    Chris: optimal bot behavior when switching from roam to seek would likely cause the bot to spin around looking for the beacon to see if its visible from current position anyways. Then if no beacon is found, travel in a direction which there is no object avoidance IR reflection (meaning a clear pathway) travel a ways and repeat the spinning action. It seems this behaviour would be the same regardless if the becon is constant on or relay responsive.
  • Rusty78Rusty78 Posts: 33
    edited 2005-04-04 20:10
    Hey dudes,

    ················A very basic question, please forgive me, but how are you able to know that the boe-bot batteries are running low..I mean via the·Baisc Stamp...is there a·special function to do this?

    Cheers

    R.K.
  • Paul BakerPaul Baker Posts: 6,351
    edited 2005-04-04 20:21
    There are nearly as many different means of doing this as there are hairs on your head, but all of them require some amount of external components and/or circuitry. It typically involves knowing the chemistry of the batteries you are using and its discharge curve and·comparing the voltage on the battery to some threshold that corresponds to a certain percentage battery capacity. All current battery chemistries have a non linear voltage change through discharge that looks like a first order lowpass frequency plot, ie straight and level (with a small amount of sagging) that at a certain point decreases rapidly, this decrease corresponds to the battery's end of life and knowing the chemistry of your battery and your load (how much current are you drawing) you can calculate how much time you have between the detected battery low condition and how long before they are no longer useable.
  • allanlane5allanlane5 Posts: 3,815
    edited 2005-04-04 20:38
    In short: to find when your battery is discharged, you measure the battery's voltage. Now what Paul said is that each battery chemistry (NiCd, NiMh, Alkaline) has a different discharge-voltage curve, so you'll want to find the curve for your battery, for your useage pattern.

    Once you know that, you should be able to reliably measure the battery voltage, and know (from testing) how much longer you can use that battery.

    And you measure the battery voltage using the RCTime command to charge and then measure the discharge time of·a capacitor I believe.· There's a few examples in the Nuts&Volts articles, I think.
  • inakiinaki Posts: 262
    edited 2005-04-04 22:45
    In Nuts&Volts July-95 there was an article about how to check· battery using a led, a photocell and the POT command in the BasicStamp. It is among the articles collected by Parallax from Nuts&Volts.
  • Ray IddingsRay Iddings Posts: 47
    edited 2005-04-04 23:33
    inaki - thanks thats good to know.

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  • JimmioJimmio Posts: 43
    edited 2005-04-18 21:17
    JUST LIKE THE ROOMBA DISCOVERY!
    the robotic vacumn cleaner. When its batteries are low it searches for an IR Beacon coming from its base.
    Price $250
  • Ray IddingsRay Iddings Posts: 47
    edited 2005-04-26 00:48
    Just a quick update on my self charging project...I HAVE FAILED SEVERAL TIMES, WOOHOO!!!



    I'm gonna put together some pics of my disasters and my code (what a mess) and hopefully you guys can help me. Love the failures..hehe



    Ray

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