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arbotiX, Propeller and/or Serializer? — Parallax Forums

arbotiX, Propeller and/or Serializer?

PropBotPropBot Posts: 13
edited 2011-05-12 21:43 in Robotics
Hi All,

The quick of it:
Can two DC motor driver carriers be added to a(any) of the Propeller boards?

Background:
I'm in the planning stages of building a crawler bot, the left and right treads of which will each be powered by a DC motor that draws under ~20A under full load (so far, testing indicates a peak draw of ~16A). I will also be installing two motors that draw under ~2A peak and two that draw under ~1A peak.

For the ~20A loads I'll be using a 30A-rated DC motor driver carrier connected to either the arbotiX (with a Serializer WL connected to it), or a Propeller board (as to a Propeller, I'm leaning towards the Robot Control Board as I can run the ~2A motors off of it [as a secondary consideration], and am alternatively considering the 3C as well).

Expounded questions: In order to run all six of these motors (plus five servos of up to 200 oz.-in. capacity), do I need to add - and can it be done - two motor shields or can I can I just add the one? I am confident that the Propeller Robot Controller Board will be able to handle the two ~2A motors, but does it also have the connections to drive the ~1A motors with the 30A board connected as well?

Advice greatly appreciated.

Comments

  • Martin_HMartin_H Posts: 4,051
    edited 2011-03-27 15:26
    That sounds like one large robot, much bigger than anything I've ever built. I would think your power supply and motor controller would be the issue and not the choice of microcontroller. Most motor controllers have a logic level power and inputs, and a motor side power supply and outputs. The propeller has plenty of i/o pins to control any motor controller out there.
  • PropBotPropBot Posts: 13
    edited 2011-03-27 21:09
    Thanks for the speedy reply Martin, much appreciated.

    Actually, each "20A" motor is powered by a 2000mA, 12.5V battery pack; I'll have to test the four other DC motors when I get them, but I don't expect them to need more than [1400]mA, and I'll get another 2000mA battery for the servos.

    As for the robot itself, I don't expect the body of the crawler to be bigger than 18" long, 12" wide and nine inches high, with some of the servos adding about six inches in length and the rest about eight inches in height, and neither of those latter two arrangements adding much weight - well, in comparison to the body that is to say.

    Regards
  • Duane DegnDuane Degn Posts: 10,588
    edited 2011-03-28 07:53
    PropBot,

    There was a recent discussion about motor controller here:
    http://forums.parallax.com/showthread.php?130365-(Need-Advise)-RC-ESC-or-L298

    There might be some ideas there that could be useful with your smaller motors.

    I don't think I understand your last post. You describe the battery for your "20A" motor as "2000mA, 12.5V battery pack". Batteries are often described by their capacity in mAh (milliamp hours) and by a "C" quantity (an indicator of the current it can deliver). I hope you not trying to power a 20A motor with a battery that can only deliver 2A.

    What kind of battery pack is it? SLA (sealed lead acid), NiMH, LiPo etc? 12.5V seems like an odd voltage (10S NiMH would be 12.0V, 3S LiPo would be 11.1V).

    What are the two smaller motors used for?

    If you're really using four ~16A motors on this robot, it should be able to crawl straight up with you sitting on it. That thing could be dangerous.

    Do you have any more information about the motors you could share? A link? Datasheet?

    As Martin pointed out, the motor controllers are going to me the trick. I think the Propeller is a very good choice for a microcontroller to use with this bot.

    I hope you keep us informed on your progress.

    Duane
  • PropBotPropBot Posts: 13
    edited 2011-03-28 14:25
    Thank you very much for your reply Duane - as with Martin's it was timely, helpful and informative.
    Duane Degn wrote: »
    ...I hope you not trying to power a 20A motor with a battery that can only deliver 2A...
    uhm, a motor with obviously 1000% efficiency is pretty normal in my universe, isn't it in yours? ^.o

    Being the start of the week I'm pretty jambed by my "real" job, but let me see what I overlooked, misread, incorrectly tested, etc., etc., etc., and I'll post back within a day or two. And yes, I will be happy to, and was planning to, post updates on the bot as noteworthy progress is made.

    Thanks again.
  • PropBotPropBot Posts: 13
    edited 2011-05-05 13:19
    Update:

    I've re-tested the one "20A" motor that I have and it does indeed peak at just over 15A under load - with a full charge of the battery. This actually caused me a bit of confusion, since my inexpensive DMM lists a maximum testing value of 10A on a fused circuit. In shopping for a DMM with data output I came across an upscale DMM from the same company, which listed the same 10A maximum current testing ability - but with a 20A max for up to 30 seconds. I am quite knew to electronics and robotics, so I'll have to do additional reading of my DDM's user manual to see if I can determine the battery's amperage output. If anyone knows of a pretty decent DMM with data capture and/or USB data out and preferably under $100 please post about it!

    I'll be using two of these motors, hacked from two Ryobi 9.6V cordless drills. I don't know if they're brushless motor or not; I'll be using the NiCad battery pack that comes with it in its original packaging - although I will look into getting and using [LiPo] packs instead. BTW, it's the charger that's 2000 mA 12.5V.

    This crawler is eventually going to have a pair of servo-based gripper arms, and since it's also going to be entered into a mech-bot competition as well, it was going to have a set of airsoft-style light weight (~1A) BB guns and a set of heavier (~2A) airsoft "Defender" class guns. Recently there's been some questions about the durability of the lighter weight guns, so I may have to find alternatives for them or go with four of the heavier guns.

    Regards
  • PropBotPropBot Posts: 13
    edited 2011-05-07 15:36
    Update:
    Due to it's (advised) inability to multi-task, I've eliminated Arduino-based controllers from consideration for this project, which leaves me to choose between either the C3 or the Robot Control Board.

    Question #1:
    I see that either board will output at 5V, but I'd like to maximize output of the AX-12(x) servo's I'll be using, which are recommended to be run at 11.1V to do so, so how would I accomplish that with either of the afore mentioned boards?

    Question #2:
    I want to run Parallax sonar and IR sensors, but a PhidgetSpatial 3/3/3 IMU. Unfortunately I now cannot find the reference, but earlier today I'd seen a link that stated this IMU needed to be connected through a Phidgets 8/8/8 board; if this is the case, can I connect the 8/8/8 to either of the Propeller boards - and is this a duplicity of abilities?

    Comments and/or recommendations would be greatly appreciated.
  • Duane DegnDuane Degn Posts: 10,588
    edited 2011-05-08 00:28
    I'm not sure why you'd want to use either the C3 or the Robot Control Board.

    The C3 is a very nice board but it has lots of stuff you probably wont use. The Robot Control Board seems like a better choice except the H-bridges aren't beefy enough for your motors. I think you'd be better off with a Propeller Proto board and add the motor control components yourself.

    AX-12 controllers need a power source between 7V to 10V (Recommended voltage: 9.6V). I'm not sure where you got the 11.1V figure (probably from someone using them with a three cell LiPo). Depending on your battery voltage, you might be able to power them directly from your battery pack. The AX-12 take care of the motor control for you. There are a couple of objects for the AX-12 controllers in the OBEX. A Propeller can control them just fine (as long as you don't set the baud to 2Mbps).

    If your battery voltage is too high you can use a 1A regulator if you're only using one AX-12. If you're using more than one AX-12 you might want a 3A regulator.
  • Duane DegnDuane Degn Posts: 10,588
    edited 2011-05-08 00:39
    Okay, I went and looked at the Phidget boards.

    You don't want to get either of those boards to use with the Propeller. They need to be used with a computer.

    The IMU board can not be connected to the 8/8/8 board. Both boards require a USB host (i.e. computer).

    There is a USB host object that has been made for the Propeller but it is far from plug and play. It also requires 4 cogs (I think).

    I personally think you'd be better off using a different IMU solution. I think they've been discussed in some of the quad copter threads.
  • Duane DegnDuane Degn Posts: 10,588
    edited 2011-05-08 00:58
    I've spent some more time at the Phidgets site.

    PhidgetSBC2 is the board that can control the IMU device you mentioned.
  • PropBotPropBot Posts: 13
    edited 2011-05-08 09:43
    Hi Duane, thank you for very much for your thoughtful replies, your time and efforts are quite greatly appreciated!

    I've actually been leaning towards the RCB for most of the time, and as advised by Martin above and elsewhere I would be using a driver carrier, most likely the Pololu Dual VNH2SP30 board.

    While I'm laying the groundwork for this project, I'm actually undertaking a turret project first, and I'll get my initial exposure to servo's with it - lol, presumably I'll learn to wire servo's with it!. I'd gotten the 11.1V value from a Robotis page detailing the AX-12 family of products, including the new AX-12A (the "11.1V" reference is under the "H/W Specification" section).

    Much to my chagrin considering your replies, I have to admit that I've just been persuaded to reconsider implementing an IMU on my turret project (rightfully so I should add), and as such I've decided to postpone the same for the crawler as well - at least until I have a much better grasp of the technology. I have additionally bookmarked the PhidgetSBC2 page though, and will be acquainting myself with the technologies involved as I progress through the turret and future projects.

    Again Duane, thank you very much for your replies as they have been particularly helpful.
  • Duane DegnDuane Degn Posts: 10,588
    edited 2011-05-08 12:08
    Thanks for the link to the Robotis page.

    The page seems to imply all the AX-12 controllers can use 11.1V. I hope this is correct.

    The manual I have for my AX-12+ controllers states the voltages I listed. It would be nice if I could use a 3 cell LiPo with my AX-12+s.

    If you have AX-12A controllers then the 11.1V should be fine.

    I don't see a problem with the Pololu motor board.

    I still wonder why you want to use the RCB. You wont be using the motor controllers on it. You don't need it to control AX-12As (you would also have to modify it a little is you do use it). AX-12s don't use the same communication protocol as normal hobby servos (you probably already know this). They also need pull-up resistor on the communication line (you'll also want to include a series resistor 4.7K so you don't damage the Propeller chip from the AX-12s incoming communications).

    I think a Propeller Proto board would work fine for your needs (as I understand them). And you could buy four USB Proto Boards for the price of one RCB.

    One thing the RCB has going for it is the level shifters. There are a few servos that wont work with a 3.3V signal (not many servos are this picky). The RCB should work with all normal hobby servos. If you do happen to have one of these picky servos you can still control it with a Prop Proto Board. It just requires an extra transistor.

    You might have noticed I'm a fan of the Propeller Proto Boards. You can buy the non-USB version for $20 (if you buy five at a time).

    I don't know if you've used the AX-12 controllers before. I have a bunch and they are really cool.

    I started into this robot stuff a couple of years ago and it has been a blast. I've always wanted to do it. I finally have a little spare time and enough money for the parts (much of the cost is tax deductible because I use the parts with my work). The Propeller is the perfect microcontroller for doing this kind of stuff.

    Duane
  • PropBotPropBot Posts: 13
    edited 2011-05-08 13:58
    @Duane: you're welcome and thanks for your reply :)
    I'm still leaning towards the RCB because I am so new at this that I simply feel more comfortable with obtaining a controller that encompasses my (perceived) needs right out of the box. I will study the differences between the RC and USB Proto boards before making a decision though - the price point on the USB Proto is certainly compelling!

    And no, I didn't know about the different protocols - I am very new at all of this. I'm mechanically inclined and I have had (and am taking) programming classes, but I am only casually aware of electronics - I recently bought a copy of "All New Electronics Self-Teaching Guide" (authored) by Harry Kybett, (and revised by) Earl Boysen (ISBN: 978-0-470-28961-7). It looks promising and I'm sure it will help give me a better grounding in what I'm doing.

    The afore-mentioned turret project is the first exposure I'll have to actually building anything with electronics, so I do have a long ways to go, but I'm already enjoying myself quite a bit just doing the research to get my projects started off on the right foot! :)
  • PropBotPropBot Posts: 13
    edited 2011-05-12 21:43
    Update:

    I've pretty much decided to go with the Propeller Proto Board. With that, I'll be starting a new thread here for the build I'll be incorporating the board into, and won't be posting to this thread anymore other than in reply to someone else.

    My thanks and gratitude go out to you Duane and Martin for your help, very much appreciated!
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