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Torque? — Parallax Forums

Torque?

Monkey4saleMonkey4sale Posts: 28
edited 2007-01-20 16:30 in Robotics
Can anyone explain torque to me? I have a boe-bot and according to the specs on the servo they can handle 47 oz to an inch. But what does this mean? i just dont get it.

Comments

  • FranklinFranklin Posts: 4,747
    edited 2007-01-13 19:11
    47 inch ounces means the device can hold 47 oz on an arm 1 inch long or any combination thereof. (23.5 oz @ 2 in)

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    - Stephen
  • Monkey4saleMonkey4sale Posts: 28
    edited 2007-01-13 20:15
    so how do i figure out how much i need to drive a robot?
  • Mike GreenMike Green Posts: 23,101
    edited 2007-01-13 20:27
    Monkey4sale,
    You have to figure out what you want the motor/servo to do and how you're going to connect it mechanically. For example, how fast do you want your robot to go? How big is it? How heavy is it? What kinds of wheels are you going to use? How big are they? Are they connected to the servo directly or via some kind of pulley system or gear system? With the example Franklin mentioned, do you have 1" diameter wheels or 2" diameter wheels? The smaller wheels would have more "push" (47 oz of force) than the larger wheels (23.5 oz of force), but wouldn't move as fast along the ground. If you don't have good traction, the larger force may not be useful because the wheel will slip. Usually people start with what they want their robot to do, figure out the mechanical forces involved, then get a motor that has some extra capability. If they then find out that the motor is too big or takes too much power, they scale down their plans to something more practical.
    Mike
  • Monkey4saleMonkey4sale Posts: 28
    edited 2007-01-13 20:32
    Well the olny thing I know so far is maybe the diameter and that will probably change, I built the boe-bot from the kit and im trying to build a bot using its board and servos and then build the base for it.

    This gets more and more confusing.

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    When you see the pretty smoke come from a component. It is time to go shopping again.
  • Mike GreenMike Green Posts: 23,101
    edited 2007-01-13 20:43
    It shouldn't be confusing. There just aren't any specific answers without more information. It's like asking what kind of car should I buy? That depends on what you want or need to use it for, how much money you have to spend, what's on the market now, do you really care what it looks like or how efficient it is, etc.
  • FranklinFranklin Posts: 4,747
    edited 2007-01-14 02:25
    Sorta like how long is up? tongue.gif

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    - Stephen
  • PARPAR Posts: 285
    edited 2007-01-14 02:45
    Monkey4sale said...
    Well the olny thing I know so far is maybe the diameter and that will probably change, I built the boe-bot from the kit and im trying to build a bot using its board and servos and then build the base for it.

    This gets more and more confusing.

    Think of it not as "confusing" (which it may currently be to you), but rather as the first step on a journey of increasing complexity. You get to travel along that path at the pace you feel comfortable with, and you will definitely learn a lot along the way. Most folks who take that journey enjoy it as "the trip is the thing", and pursue the hobby exactly for that reason.

    So, you built the BoE-Bot and it's now running, right?

    And, now you want to use the same BoE and the same two servos to build some other style (base, you said) of robot, right?

    Do you want this new robot to be exactly as capable as the original kit robot (the BoE-Bot?)?

    If so, then you know a lot about what design criteria you must approximate or meet, such as "it goes only so fast", "it can carry only so much extra weight", "it can climb up an inclined plane that is only so steep", "it uses up battery power this quickly when performing such and such a task continuously", etc.

    Challenges? Maybe you want to try to use those motors and that size/capacity of batteries with your BoE to build a differently-shaped/engineered robot that can climb up a steeper incline, or one that can go faster, or one that can travel further on a load of fresh batteries?

    Anyway, think of it as "fun", "challenging", "learning new things", etc. And, let the "confusion" just alert you to the fact that there are yet new things for you·to learn in this hobby.

    PAR
  • Monkey4saleMonkey4sale Posts: 28
    edited 2007-01-14 02:54
    alright, well i have spent most of the day meddling with autoCAD and not getting very far but so far my parts list includes:
    1 threaded swivel caster
    2 wheels ~ 2" diameter
    Im probably just going to screw a servo horn onto the wheel and connect it to the servo for my connection. But i have no idea on the weight of the thing. It is going to be smaller then 8" by 8" cut out of high density polyethelene(hope i spelled that right). So if im using 2 inch wheels then im guessing that my robot needs to weigh less then 23.5 OZ.

    This is my original idea to see if i can just redesign a different look for it, this is for multiple reasons and the top to are to see what i can do and to make people stop saying that the robot is tiny and worthless lol.

    so far this is what i have come up with the things on the sides are the servos, they are going to be a layer lower and the drill hole is for the caster.
    robot1.jpg
    ·

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    When you see the pretty smoke come from a component. It is time to go shopping again.

    Post Edited (Monkey4sale) : 1/14/2007 3:03:36 AM GMT
  • PARPAR Posts: 285
    edited 2007-01-14 03:02
    Monkey4sale said...
    ...
    and to make people stop saying that the robot is tiny and worthless lol.

    Well, great! You can reply to them, "How big should it be?", and "What should it be able to do?"

    Whatever answers they give you, then you can simply observe, "See, my robot isn't so tiny and worthless afterall. It got you to thinking --and that's good!"

    :>)

    PAR
  • Monkey4saleMonkey4sale Posts: 28
    edited 2007-01-14 03:09
    lol, i was originally going to try and recreate the hexcrawler for cheaper then the 600-700 dollars advertised since all of the measurements are listed in the pdf but i figured i had better figure out the basics of design before i got in over my head [noparse]:D[/noparse]

    and am i right about the robot needs to weigh less then 23.5 oz? and i notice the boe-bots wheels are 2.5 inches in diameter so that would mean that you cant addon anythign that would make its overall weight greater then 18.8 oz. Am i getting these figures right?

    do you like the little fellow? its 6.4 wide and 8 long, has no use but maybe i can use it for TSA.

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    When you see the pretty smoke come from a component. It is time to go shopping again.
  • PARPAR Posts: 285
    edited 2007-01-14 03:22
    Monkey4sale said...
    ...
    and am i right about the robot needs to weigh less then 23.5 oz? and i notice the boe-bots wheels are 2.5 inches in diameter so that would mean that you cant addon anythign that would make its overall weight greater then 18.8 oz. Am i getting these figures right?
    OK. Time for you to get out your weights and scale. Put different amounts of weight onto your BoE-Bot, tie a string to its rear and the other end to a scale (the kind that when anchored at one end and pulled at the other to indicate weight). See how much load your bot can take before becoming stuck. See how fast it can move under different loads. See how much pull it can exert on the scale under different loads before slipping or stopping.

    Increase the wheel diameters, and do the tests again.

    Don't stall the servos for more than a moment, and don't let them run too long under stress, or they·may burn out.

    This should reveal a few more questions, and maybe an answer or two,·to you.

    PAR
  • Monkey4saleMonkey4sale Posts: 28
    edited 2007-01-14 03:27
    lol, i havent even ordered any of the parts for it, im just sketching ideas, now lets add to my shopping list: 1 scale
    the only thing that i have which isnt from a kti and is not a normal house hold item is a soldering gun, which i have burned myself with....many times......on one project.....to learn how to solder.

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    When you see the pretty smoke come from a component. It is time to go shopping again.
  • PARPAR Posts: 285
    edited 2007-01-14 03:43
    Monkey4sale said...
    lol, i havent even ordered any of the parts for it, im just sketching ideas, now lets add to my shopping list: 1 scale
    the only thing that i have which isnt from a kti and is not a normal house hold item is a soldering gun, which i have burned myself with....many times......on one project.....to learn how to solder.

    No, no, no...· Use your BoE-Bot, that you said you've been using for a year or more.

    Learn how it performs under differing loads, and get some ideas from that about the issue of "torque" and design requirements for your newly-planned bot.

    PAR
  • Mike GreenMike Green Posts: 23,101
    edited 2007-01-14 05:04
    You've mentioned several times about the robot weighing less than 23.5 oz. The weight of the robot is an issue for the strength of the wheels, the axles, and the motors and their mountings (if you step on it, your weight may break the wheels or the motor shafts or mountings). If the robot is moving along a flat surface, the motors have to overcome the friction of the wheels, that's all. They don't have to lift the robot against gravity. If the robot is going up an incline, it will have to "lift" a percentage of its weight depending on the angle of the incline (work it out - it's simple mechanics - if you don't remember it, get a book from the library on basic physics - this is basic stuff for robot construction or any kind of mechanical construction). If the incline is steep enough and/or the robot is either too light to develop enough friction or too heavy for the friction to hold it in place, it will slide down the incline and the strength of the motors/servos won't matter.

    This is why you need to experiment with different scenarios with your existing BOE-BOT. Run it up an incline and see what happens. When does it begin to slide (or fall over if it's top-heavy)? When does it stall or slip? See what happens when it pulls a block around (without wheels ... so it drags). What happens when you put skids on the block? How heavy a block can it pull? How heavy a weight can it lift straight up if you attach it via some pulleys? When does it begin to skid? Does it help to weigh down the BOE-BOT? When do the servos stall? Boy, you can spend hours and hours just figuring out what your BOE-BOT can do now.
  • Monkey4saleMonkey4sale Posts: 28
    edited 2007-01-15 16:05
    simple mechanics, basic physics, lol, Hard to remember that when you are a freshmen in highschool. Im already accelerated in programming and the only one who knows anythng about robots in TSA. So now i need to learn physics and mechanics?

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    When you see the pretty smoke come from a component. It is time to go shopping again.
  • John R.John R. Posts: 1,376
    edited 2007-01-15 16:27
    Monkey4sale said...
    simple mechanics, basic physics, lol, Hard to remember that when you are a freshmen in highschool. Im already accelerated in programming and the only one who knows anythng about robots in TSA. So now i need to learn physics and mechanics?

    Ah, err, think about this.· You want to design a robot.· A robot is mechanical, and from a "physical" viewpoint, must obey the laws of physics.

    Kind of hard to just "ignore" them (Mechanics and Physics).

    This combination of mechanics, physics, electronics, programming, etc., is what draws many of us to the world of robotics.· Nobody said it would be easy.

    Fortunately, much of what you need to learn isn't as complicated as you would make it out.· Try some of the experiments mentioned in this thread.· Even if you don't understand the "physics" or the math, you'll "get a feel" for these issues, and how they affect not just your robot, but also other things in the world around you.

    We all have a very good understanding of physics and mechanics, we just don't realize it.· When someone throws a ball (or even better a "frisbee")·at you, whether you realize it or not, you have an understanding of Accelleration of gravity, projectile paths, (for a frisbee, add aerodynamics, lift, friction of the air) and a whole lot of other stuff.· You understand them well enough (or most of us do) that you can catch the object.

    You also understand that a car is harder to push uphill than down, and that a car with a flat tire is harder to push than one with good tires.· You also understand that if you turn the handle bars on a bicycle, it will turn, and if you don't lean, you'll probably fall over.

    These are all examples of mechanics and physics.· You may not know, or care, about the math involved, but you understand them.· Adding the formulas and math just puts numbers on what you already know.

    There are a lot of robots designed and built without a sheet of paper or single calculation.· But these are made by gaining a "practical" understanding, either by experience or experimentation (as has been suggested).

    There are no "set answers", just a path we can set you on.


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    John R.

    8 + 8 = 10
  • WarrlokWarrlok Posts: 77
    edited 2007-01-16 03:11
    hey all , i got a mattrack boebot with a heavy battery pack and a heavy camera and a combination pantilt and claw from lynxmotion ,, it uses the same cr servos but it about half the speed of a normal boebot and its got pleanty of power.·· ·biuld it with the wheels or tracks on the outside and then and on if needed they have stronger servos and geared motors if that not fast enough(starts to get expensive with h-bridges and motors)

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    Problems are the "roads" of life,
    solutions are only "onramps" to the next problem



    ············································· "Brad Smith"
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  • Aaqil KhanAaqil Khan Posts: 60
    edited 2007-01-19 18:35
    To sum it up really quickly, what you need to build a "good" robot is a little knowledge in the following fields:
    -mechanics (both dynamics and statics)
    -newtons laws (the above depends on this one too)
    -electronics (to build basic analog and digital circuits)
    -programming (to tell the robot how to behave "think")

    let me know if i missed somethign. i designed a robot arm and those items mentioned above helped me make a good robot.

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    E=mc^2
  • LSBLSB Posts: 175
    edited 2007-01-20 16:30
    Serveral years ago I put together a "Letterman style Top 10 List" for robot building-- I still reveiw it before starting a new project. For those who wonder if the frustration ever fades, here it is (read from the bottom up)...

    Top 10 things to remember while assembling your robot

    1. Buy scrap, 85% of the time it saves a step.
    2. AI will have reached the epitimy of usefulness when a robot can deal with the legs of a 5-caster office chair
    3. The suitability of any part for a particular purpose can be determined by count-- if you have one less than you need, its the right part.
    4. Band-aids make it hard to hold tweezers.
    5. Resistor color bands are heat sensitive and change color while being soldered.
    6. Just because the light isn't on doesn't mean the soldering iron isn't hot.
    7. BASIC isn't, squares aren't, screwdrivers don't, and sensors hardly ever will. The only component aptly named is the resistor.
    8. Multi-meter is a fancy name for a random number generator.
    9. C is for people aren't frustrated by golf and find chess stupidly simple.
    10. It's not too late to become a TV sports fan.
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