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Thread: Please help me!

  1. #1
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    Exclamation Please help me!

    I'm new to this forum and fairly new to the electronics aspect of robotics. The information online is very confusing, maybe someone can help clarify it for me. Will my 400 watt 12 vdc battery be able to power 4 x Banebots 64:1, 36mm Planetary Gearmotor, RS-540 Motor http://www.trossenrobotics.com/store...540-Motor.aspx? I don't know how to understand amp calculations. I had thought a 12vdc 400 watt battery would provide only 33 amps, but this website says that a 3.3ah battery can provide 60 amps continuous; I don't understand http://www.robotmarketplace.com/prod...-3300N-12.html. My rover will be about 20 lbs., so if I can't use those motors with my 400 watt battery, what should I use? Also, how much torque should I have to move 20 lbs.?

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    Re: Please help me!

    First, welcome to the forum!

    Second - your battery is, I assume, 400 watt HOURS, right? Or specifically, 33Ah, right? Amps = Watts/Volts Watts = Amps * Volts (roughly, we're assuming no resistance for the moment).

    The measure of Amp Hours or Watt Hours is a little touchy. The basic concept is: "How long can this thing deliver power to my device, what point will it fall to a point that it won't operate anymore".

    Assuming that you have enough torque with four of those motors to operate at a kind of medium current draw, we see that the motors will draw somewhere between 1A with no load, and 42A if the motor is stalled (which you really don't want to do).

    Let's just pick a number and say we want to put 20A into each motor. That's 80A total. A 33Ah battery would power the motors for somewhere in the neighborhood of 20 mins.

    You didn't note what kind of motor controllers you're using, and you didn't note what technology battery.

    A 33Ah gel-cell can deliver almost 400A into a direct short to ground (which is basically what a stalled motor is) in my experience. And a LiPo can burst into flames and burn your house down quickly. It's ALWAYS important to fuse them under what the stall current is!

    Anyway, if you can give us a bit more information - what size are your wheels, are you doing any other gearing, are you open to doing any other gearing, what kind of motor controllers, what kind of battery technology, ... then we can probably help out more!

  3. #3
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    Re: Please help me!

    Thank you for the prompt reply. I intend to use 5" wheels. Here is the website for my battery http://www.batterygeek.net/product_p...atterygeek.htm. My rover will use BaneBots Motor Controller (45A peak) if I use the Banebot motors. How much torque is required to move a 20lb. robot? What type of battery should I use and where can I buy it? I want enough power to last for hours of use. Thanks

  4. #4
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    Re: Please help me!

    I'm swamped, and hopefully someone else will come along shortly.

    I'm going to write a tutorial on this as soon as I have a few hours. I promised Alex I'd do it at some point...

    [I'm just going to bang some rough numbers and assumptions and deal with explnation later]

    0.0052083 * in-oz = lb-ft

    About 11ft-lb at peak (not stalled) per motor
    44ft-lb total.

    After running the numbers, I would guess that your four-motor design on a 20lb bot with well inflated 5" rubber tires would be able to climb a 20 degree incline max on pavement, would have a top-speed of 3 ft/sec, and would get there at 0.5ft/sec^2. If you need less climbing, we can regear it and get some more speed or acceleration...


    Your motor controller isn't big enough. You would need four of those motor controllers.

    How are you going to turn - slip-skid or servo-based steering car-style?

    Hours of battery? More of those batteries (ouch) or increase the robot weight and add cheaper battery technology...

    Sorry - brief answer, I know. I'll put my numbers out there so everyone can check 'em this evening...

  5. #5
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    Re: Please help me!

    OK, so 4 x BaneBots Motor Controller (45A peak) and 4 x Banebots 64:1, 36mm Planetary Gearmotor, RS-540 Motor. Do you think those motors are overkill for a 20lb robot? I certainly can't spend more than $1000 on battery power, so what would you guys recommend using? My issue with all this is that this is a house bot. I want long lasting, lightweight, and efficient. If we don't count batteries and motors, my bot will weigh only 8 lbs. There must be a simpler way to move around such a bot. I'm not as experienced as you guys.

  6. #6
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    Re: Please help me!

    What do you need the bot to accomplish? My little competition bot weighs 7lbs with batteries, runs for 1hr 15mins at full power, can climb a 45deg incline, and moves about 1.5mph. Total out-the-door build cost is about half of one of your batteries, including batteries.

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    Re: Please help me!

    M'mmm this is an interesting post and could go on for a while, Before any of this can be calculated as Adrenalynn has stated you have to provide all of the information that you want your bot to do, This is very important in deciding how to approach your requirements Judge, But it sounds like you and Adrenalynn are in control of this now. Good luck with your project.
    People yearn after this robotic dream, but you can't strip your life of all meaning, emotion and feeling and expect to function.


  8. #8
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    Re: Please help me!

    Please, by all means jump in, M'!

    I found another quantum singularity in my garage. Beating it back is occupying all my resources.

    Where'd I put that spare warp-core? Gonna need it to power those superconducting magnets...

  9. #9
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    Re: Please help me!

    Well, my goals for this robot are mainly accademic. Physically, I want him to drive around on a level surface indoors. It's simply a rover with a brain. However, I don't want him to last for an hour or even 5; I want him to last all day like 12 hours. My original plans (using the 444wh battery and 4 x Lynxmotion motors) would have lasted for many hours, but then I realized I didn't have enough torque to move an 8lb bot and 9lb motor . I could use my old gel-cell wheelchair battery to power the Banebots motors and a 200 wh battery from BatteryGeeks to power my sensors, etc., but then I might just have a reoccurring problem. Heavier batteries require stronger motors that need more current and bigger batteries. Where's the perfect balance?

  10. #10
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    Re: Please help me!

    12hr runtimes? Sometimes reality must impact our desires...

    Maybe it's time to start thinking about how often you're willing to chase it down and drop in more batteries?

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