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Boe Bot gripper problems — Parallax Forums

Boe Bot gripper problems

artmakerartmaker Posts: 9
edited 2006-01-02 17:44 in Robotics
My son is having problems with the new gripper I bought him.
If you manually turn the servo the gripper will do what it's suppose to. But when he programs it, the thing will barely open the gripper and gets stuck. It hums like it's trying to work but can't. We read through the posts here and he tried switching wires. no good. The parts all move freely so I don't think this is a mechanical hang up. It just behaves like it doesn't have the power to move the parts.


I noticed, the instructions are really vague as to how to attach the wires to the claws. We had to guess on that. Again, if you turn it manually it works fine.
He also said he tried flipping the plug around. Also no good.

Any clues? Is this a bad servo? We don't have another to swap and try.

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-12-27 23:16
    Hello,

    ·· Flipping the plug around is definately a bad idea, since the connector is polarity specific and should only go in one way.· What code are you using to open/close the gripper, and which BASIC Stamp are you using?· Have you tried a fresh set of batteries in case that's causing a problem?· And finally, have you adjusted the PULSOUT value to a value further from 750 than the one you're using now?

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • artmakerartmaker Posts: 9
    edited 2005-12-28 01:13
    wow, wasn't expecting a reply so fast!


    I just bought this boe bot for Christmas. Fresh batteries. The regular moving functions just fine.
    It's the usb version (mac user here.) As for what BASIC stamp,
    BS2.

    Yes on the PULSOUT value to a value further from 750 than the one you're using now question. And in "several directions." Here is one he tried.

    i var word
    for i=1 to 200
    pulsout 14, 650
    next
    end

    He tried putting in any number he could think of in place of the 650.

    Sometimes the grip will try to open just for a split second. Sometimes it won't even do that.

    He tells me the servo seems to be turning the same direction no matter the number he types in.

    Additional, he tried getting the IR to work and had problems. (Perhaps that's for another thread?)
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-12-28 01:55
    Ah, I think I see the problem.· There is no PAUSE 20 within the loop.· You are over-driving the servo.· Put a PAUSE 20 right after the PULSOUT and try your numbers again.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • artmakerartmaker Posts: 9
    edited 2005-12-29 00:41
    Nope, tried that. Same result. The thing tries to move for a second, then the servo just humms.
    My son tried running the program after disconnecting the gripper arms. The servo simply will not run. It jerks and humms.
    Any chance we simply have a bad servo? And if so, (I see your with Parallax) what is the policy on swaping it?
  • John R.John R. Posts: 1,376
    edited 2005-12-29 01:34
    As Parallax is closed until next week, you might want to try one or both of the following:

    Take the servo to a radio control hobby shop, preferably one you shop at (even if you shop there for other things). These (with the exception of the continuous rotation servos) are the same servos that are used in R/C planes, boats and cars. See if someone there will connect your servo to a radio control set, and test it for you. If it works there, then you either have a wiring or code problem.

    If the servo does not work there, they should have one you could purchase for a little under $20.00 (at least around here in Wisconsin). This could get you going, but before you use it, try some of the stuff from "What is a Microcontroller" (WAM) to make sure it wasn't something you did (possibly wiring error) that blew the first servo. WAM is available for free download from Parallax.

    Independant of the above, and especially if your existing servo is found to be working: Try fresh batteries (again) and/or an A/C adapter to make sure you're getting enough power to the servo. Here it may make sense to start with some excercises from the WAM book.

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    John R.

    8 + 8 = 10
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-12-29 01:57
    If the servo is defective, we will, of course, replace it.· On the other hand, more than often we find that there is something else wrong, and we get back a lot of working items.· I would disconnect the rods and write a small program that moves the servo through it's entire range of motion.· See if it does it without the load on it.· But you do need that PAUSE 20 in there.· In any event, if that doesn't work, e-mail (Not PM) me and I will tell you how to go about the RMA.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • artmakerartmaker Posts: 9
    edited 2005-12-29 01:57
    OK, the hobby shop is a good idea.

    Looking for the WAM download now but my son is telling me he has the big book that comes with the boe bot and it is covered in there. (I'll download the WAM anyway.)

    Doubt it's the brand new batteries as this thing does everything else just fine. (He's been programing an LED display, and sound effects, etc.) And of course the wheels drive it fine.

    Is it possible we have the wrong servo? The one in the gripper kit says "parallax standard servo." But the one that comes on the wheels is "continuous rotation." (son, "I don't know..... hrumph.")

    Well, I have parallax on another window and not finding the WAM download. It's got to be burried in there somewhere.

    Yes, hobby shop. Great idea.

    Say, are you a rail fan? (your signature image there.)
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-12-29 02:00
    The Standard Servo is what comes with the Gripper Kit.· The contiuous rotation servos are only for wheels on the BOE-Bot and Sumo Bot.· The WAM text can be found here:

    http://www.parallax.com/detail.asp?product_id=28123

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • John R.John R. Posts: 1,376
    edited 2005-12-29 14:21
    Yes, I am a rail fan, and also model railroader. The model railroading is what got me "into parallax". In a "prior life" I was fairly heavy into nitro powered R/C cars (track, not dirt).

    I see that Chris got you pointed at the WAM stuff. This would be a great way for your son (or you and your son, or just you) to learn better about what's happening "under the covers". The BOE BOT is a great way to learn too, but the WAM covers some basics of the STAMP and electronics in general.

    It can be hard for young people to work through the low level stuff like they cover in the WAM book, but it is good base level knowledge. It helps teach the "why" of things, not just the "how". Even if your son doesn't have the patience for it, it might help dad understand some of the issues and become the hero. Always a good thing...

    On the continuous vs. standard servo, first, the trip to the hobby shop will answer that. If in stead of moving back and forth against the stops, if it moves round and round one way or the other as you move the "stick" on the radio, you have a "continuous rotation" servo. If it moves against a stop one way, and then the other, you have a "standard" servo.

    As another quick test, if you have the boe-bot moving otherwise, hook the gripper servo up to where one of the wheel servos is normally connected. Then lift the boe-bot up, have it "move" back and forth, and the gripper servo should also move. It won't go "round and round" but should move one side of center when driving the robot forward, and the other side of center when moving the robot backward.

    I believe the WAM book covers how to drive a servo, and also how to convert a "standard" servo to a "continuous rotation" servo. I don't know that you need to make the conversion for the sake of doing it, but looking through this section would help explain how the two servos are different, and how they work.

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    John R.

    8 + 8 = 10
  • artmakerartmaker Posts: 9
    edited 2005-12-29 16:12
    Hi John R,
    Thanks. I emailed Chris too. I think that servo is just plain bad BUT your tip on switching with the wheels is good.
    Son just woke up.
    I asked him about this. He said he already tried this yesterday. It does the same thing. It jerks then hangs up and hums.

    I have the wam download going. Can't afford the book just yet but sounds like a good idea. (Gotta pay for the bot first! Plastic got a work out.)

    Now... you said [noparse][[/noparse]Even if your son doesn't have the patience for it,]
    Oh he has the patiance. He is SO into electronics it's incredible. I swear to you, there is a job at NASA's JPL with his name on it! My husband went to college to get an electronics certification but that was over a decade ago. When he found out he's only qualified to solder wires, he kept his trucking job. BUT my kid got into all his old texts, fancy calculators etc. I bought him one of those radio kits? You probably know the kind. All the parts have springs. You folow a diagram, connect wires into the springs and make radios, buzzers etc. Well! He took the schematics, learned what all the symbols mean, looks up the actual componants on the internet to learn what they do, and BUILT from scratch on bread boards and with bags of parts from Radio Shack, his own metronome. he got extra credit in band for having one, and extra credit in science for BUILDING it!
    MY BOY!!!

    Yesterday, he took his boe bot and connected two led numeral displays. His bot can count up to 39 now! (Ran out of memory or it would have gone higher. What a tangle of wires just to do that too!)

    He's got the patiance!

    Say rail fan, I bet my husband would love to discuss trains with you. (Or any rail nut!) He's a big time rail fan. Mostly likes steam. And models. His brother is an engineer for the IC. Father was an interurban nut. In fact, several good books are out there about inter urbans with photographs from him and his friends. What part of the country are you in? We're in Michigan.
  • artmakerartmaker Posts: 9
    edited 2005-12-29 16:43
    Say another question. (This boy keeps spending MY money!)
    Would this micro processor work with the boe bot?
    BASIC Stamp 2p40 module

    We know it won't fit. But surely there is a way to configure something.
  • John R.John R. Posts: 1,376
    edited 2005-12-29 17:39
    First, my humble appologies for referring to you as "dad".· I don't think I'm sexist, but certainly did make a bad assumption in this case blush.gif

    As far as using the BS2p40, you would need to use a different "bread board" than the BOE board included with the boe-bot.· Try one of these (not inexpensive) boards:

    http://www.parallax.com/detail.asp?product_id=45187

    http://www.parallax.com/detail.asp?product_id=28138

    There is also a "starter kit" that includes the p40 and the first board shown above:

    http://www.parallax.com/detail.asp?product_id=27238

    Beacuse the board sizes are very different (these are much larger) there will be some mounting issues to be worked out with the BOE-BOT.

    On other issues:

    You don't need to get the WAM book, the book is just the "dead tree" version of the download.· You may want to get the WAM parts kit (if you don't have the parts as part of the BOE-BOT or your other electronic kits.

    I am located in Wisconsin, and we (my wife and I) do a fair amount of traveling and camping in the "not dead of winter" seasons.· We start before Road Construction Season and keep going well after Rod Construction Season ends.· I'll send you a PM with some contact info.· I'd enjoy "talking" with hubby!

    Again, my appologies for the gender blunder.



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    John R.

    8 + 8 = 10
  • allanlane5allanlane5 Posts: 3,815
    edited 2005-12-29 18:49
    1. The control signal for a servo requires a 'pulse' (low-high-low) of a certain width (1 mSec to 2 mSec) repeated every 20 to 50 mSec.

    The servo compares the width of the incoming pulse with one generated by an internal variable resistor, which is connected to the output shaft. It then turns the output shaft with a motor, until the two pulse-widths match. Note the output shaft usually can only turn through about 180 degrees, but you have reasonable control of positioning.

    A 'modified servo' has the variable resistor set to its center position, then disconnected from the output shaft. The servo also has any mechanical limits on the output shaft removed, so it can turn continuously. Thus when you give it a 1.5 mSec pulse, the shaft should 'stand still', less than 1.5 mSec it turns one way, greater than 1.5 mSec it turns the other way. This gives you an inexpensive, easily controlled wheel motor.

    Things that can go wrong:
    1. The servo requires a connection to +5 (or +6) and ground. The ground MUST be connected to the same ground as the control signal (this is OFTEN left out).

    2. The servo requires lots of power compared to the BS2. Brown-outs when trying to move the servo are common.

    3. The 1 to 2 mSec control pulse is not repeated every 20 to 50 mSec. It must be repeated.

    4. Too high a voltage is put on the servo. This can kill it.

    5. You didn't put a "LOW ServoPin" at the start of your program. This makes the "ServoPin" low and an output -- which is the necessary starting state for the PULSOUT.
  • artmakerartmaker Posts: 9
    edited 2006-01-01 17:56
    Happy New Year all.

    Update.

    We went to a local hobby shop this weekend. They don't carry Parallax but do have all sorts of radio controlled things. They found a servo that does the same thing as the one with the gripper and we tried it in the bot.
    Same result. It jerks, stops and hums.
    So, it's unlikely we have a bad servo. They wouldn't BOTH be bad. Got to be in the programing.

    I have a request here. Could someone with the boe bot, and gripper kit please post an exact snipit of code needed to make the most basic function work? My son didn't know about the PAUSE 20 thing. I betcha he is missing a few things. (His school robotics class doesn't have this kit. They are only following a maze at this point.)

    Thanks in advance.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-01-01 19:11
    You can find the demo code, which opens and closes the grippers, at the following link, bottom of the page.

    http://www.parallax.com/detail.asp?product_id=28202


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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com


    Post Edited (Chris Savage (Parallax)) : 1/1/2006 11:21:22 PM GMT
  • artmakerartmaker Posts: 9
    edited 2006-01-01 22:43
    Hi I'm the person actulaly working on the bobot my mom is the one you have been talking to.
    I pluged in the program and the sevo seemed to go further than it has before but it still only turns about 95˙ when I know the sevo is capible of 180˙ and at first I thaught the program just wasent running the sevo long enaugh so I incresed the FOR temp = 0 TO from 40 to 100 and I got the same resalts the sevo only terned about 95˙ to the right and went back all the way to the left ,but when I turn the servo tothe right and turnit back on and it turn s all the way to the left.

    If there is any chance someone could talk with me on the phone, please send my mom a private message.
    Thanks.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-01-01 23:21
    Hello,

    ·· Tech Support will be available toll-free tomorrow between 7A-5P pacific time.· In the mean time I can tell you that what you did to the program doesn't affect the rotation distance of the servo.· It only affects how long it receives pulses of a given pulsewidth.· In order to make the servo move farther you need to change the PulseWidth values which are defined as constants at the beginning of the code.· I think the default values were something like 500 and 1100.· These determine how far the servo travels.· One of these need to be changed.· You can try changing the 1100 to a 1200 and perhaps the 500 to a 400 to see what results you get.· Make one change at a time, then if you get better results, that's the value that needs to be adjusted.· Be sure not to adjust the value too far so that it hits the servo stop.· I suspect that's what is happening, and if that's the case, the rods need to be adjusted since the servo won't go any further.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • exskoolexskool Posts: 24
    edited 2006-01-02 05:05
    Hi...i also like to ask about my problem regarding to the servo..i used PSC to position the servo, however the servo doen't move·if i changed the value a little bit (i.e. from 760 to 766)..since i need high precision, a small change will be significant...one more thing, can u help me to visualize how the ramping function of PSC works (any graph??) tq
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-01-02 06:59
    Please start a new thread for new questions, that way we can keep this thread going if need be.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • artmakerartmaker Posts: 9
    edited 2006-01-02 17:19
    Thank you!!! the program it works!!!!
    now I decresed the OpenGripper CON 500 to OpenGripper CON 200 and it went about 180˙now that it works why are the programs so diferent for the 180˙ servo and the continuous rotation servo?
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-01-02 17:44
    The differences aren't really that big.· Both servos need a pulse value and to be refreshed every 20 mS.· The range of values is the same.· The difference is that the continuous rotation servos can't go to a specific position.· When they receive a center position pulse (1.5 mS usually) they stop.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
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