Shop OBEX P1 Docs P2 Docs Learn Events
Propeller Boe Bot — Parallax Forums

Propeller Boe Bot

Peter J. FischelPeter J. Fischel Posts: 28
edited 2009-01-27 23:54 in Propeller 1
I have been tempting to make my Boe-Bot more advanced by using the propeller chip.

The 8 cogs make it sound as though it is plenty of power to drive the sensors and give me room to advance my robot.

I purchased the Propeller Proto Board USB mainly because it has the same mounting holes as the basic stamp that was on my boe-bot.

What is concerning me is,· the servos. To me the Basic Stamp is really tough and I can plug the servos directly to the device no problem. However, is there anything I need to be concerned with when connecting the servos to the propeller board?· I know it has the plugs for it and I ordered the pins for it.

Please keep in mind, i have 3 servos at the moment to connect to it. 2 Drive Servos and one to rotate PING about. Ping will be another story to connect I suppose.

Do any of you mind giving me some tips?

Thanks,

Fly_Mario

Comments

  • J. A. StreichJ. A. Streich Posts: 158
    edited 2009-01-27 19:02
    I was trying to do just that, when I posted recently about certian issues. The issue is that if you use BOE's 6.5 volt battery clip, the servos draw too much power (because of the two voltage regulators). Power in both the servo part of the circuit and the microcontroller will dip too low. This caused the Prop to constantly reset when the servos are plugged in. Using a larger powersource (9v battery, higher than that and you'll blow the regulators) or powering the servos using a separate power source should correct the issue.

    I will be trying these solution this weekend, as I ran out of time last weekend. Silly work, family and church keeping me away from the stuff that really matters (j/k).
  • SRLMSRLM Posts: 5,045
    edited 2009-01-27 19:38
    I'm planning on doing the same thing sometime soon too. I'll be powering everything from a 12 volt AA pack, so regulators will be a bit of an issue for me. So, I made a servo power board to cope with it. Basically, all it does is provide dedicated 3A regulators with heatsinks that can power servos or other 5V three wire devices (like the ping or GPS) without having to worry so much about the input power or brownouts. It has the same mounting holes as the BOE and Protoboard, so I'll be able to mount it directly on top. Here's the link to the project. You can look at the PDF to get some ideas.
  • Peter J. FischelPeter J. Fischel Posts: 28
    edited 2009-01-27 19:44
    Looking at the board I purchased... since I just got it.

    http://www.parallax.com/Store/Microcontrollers/PropellerDevelopmentBoards/tabid/514/CategoryID/73/List/0/Level/a/ProductID/509/Default.aspx?SortField=ProductName%2cProductName

    There is a hefty capacator on the servo connectors.

    I am beginning to think this board should handle my servos just fine.· Anyone else familiar with that board?

    Seems to me if we have a brownout issue, we could probably put NiCads in.· Not sure the board could handle that current though.

    ·
  • J. A. StreichJ. A. Streich Posts: 158
    edited 2009-01-27 19:51
    That's the board I'm using. It's a great board. The cap is 1000uF which is enough to keep the servos powered; but that's not the issue, it's the processor itself. 6.5v (4 AA batteries) can't run the logic and servos.,, You need either a 9 volt, or a separate power source. See http://forums.parallax.com/showthread.php?p=779485 for more info.
  • SRLMSRLM Posts: 5,045
    edited 2009-01-27 19:52
    One thing that you could do is to replace the regulators with the heavier 3 amp versions that I used. Note that the pinout is different, so it will take some work (Its in-out-gnd not in-gnd-out). As long as you don't overload or stall or three of your servos at once, it should be fine.
  • Peter J. FischelPeter J. Fischel Posts: 28
    edited 2009-01-27 20:19
    Something is terribly fishy here if you're using Recharables and having this problem.

    I am heavily into RC Helicopters, I drive·5 servos (the same as what boe bot has) a Gyro, and receiver on 6 volts.

    Trust me, servos are not that picky.
  • J. A. StreichJ. A. Streich Posts: 158
    edited 2009-01-27 20:29
    It's not the servos or the prop, it reckon, it's the two levels of voltage regulators taking up the power -- best I can tell. The voltage dips, the propeller resets.

    To test, I hooked an LED to P3 and toggle it on and off at the start of the program and leave it off while the program runs.
    When servos aren't present, the program toggles and remains off.
    Hook up the servos, light toggles, the servo starts, then servo stops and LED toggles again as it restarts the program.
  • ratronicratronic Posts: 1,451
    edited 2009-01-27 20:48
    I used a 7.2 volt nicad race car battery to·a spin stamp directly and·a 5volt regulator·for the servo's. No problems
    with power glitches.·It's an upside down boebot chassis with a few erector set parts you can see in my avatar.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Fix it, if it ain't broke·
    D Rat


    Dave Ratcliff· N6YEE
  • Mike GreenMike Green Posts: 23,101
    edited 2009-01-27 21:01
    I've had a Propeller BoeBot for some time that includes a PING))) and its servo bracket, an xBee wireless link, HM-55B compass, and an SD card for programs and data, all on a Protoboard. It works fine with a 6V NiMH battery pack (5 high capacity cells with the 5th cell mounted over the pivot ball. There's a thread with a description and pictures in the Completed Projects forum and a special version of FemtoBasic (BoeBotBasic) in the Object Exchange that has specific statements for the servos, PING))) and compass. I haven't had any problems with unexpected resets although a 7.2V battery pack would give longer runtime.
  • Peter J. FischelPeter J. Fischel Posts: 28
    edited 2009-01-27 21:45
    Hey Mike! Thanks a ton for your reply. This sets me on a good path!

    Also, does the input on the servo need any extra part such as a resister between the prop output and the servo or is it fine?

    again, thanks!
  • Mike GreenMike Green Posts: 23,101
    edited 2009-01-27 22:05
    I think it was Paul Baker that recommended using a 1K resistor between the Prop output and the servo input, mostly to reduce the noise conducted back from the servo to the Prop. In any event, I put them in when I wired up the servo headers on my Protoboard.

    I also used a PCA9554 I2C I/O Expander to handle the HM55B compass so I could have an SD card and TV output and keep the VGA output and keyboard and mouse connections on the Protoboard. If you're willing to give up the TV output or VGA output, you don't need the PCA9554.
  • Peter J. FischelPeter J. Fischel Posts: 28
    edited 2009-01-27 23:54
    Yeah, I see the problem. For me to even switch from safe mode to servo mode causes a brownout with everything including my uOLED display causing a reset.

    Time to do like Mike suggests and mount NiMH batteries.
Sign In or Register to comment.