Register To Comment
Page 1 of 2 12 LastLast
Results 1 to 10 of 16

Thread: University featherweight battle

  1. #1
    Roboteer

    Status
    Offline
    Name
    Sam Betts
    Posts
    6
    Post Thanks / Like
    Hey everyone, I've recently been set the challenge to build a featherweight robot for a battle that will take place at the end of March. I would like to implement a flipper into my design if possible, I have read through lots of forums over the past few days trying to get an idea as to what some of the terminology means, what components I will need and where to buy it.

    This will be my first time building a robot and I'm in a group with 6 other people who all have no experience either. Seeing as we are students we don't have much money to spend on equipment therefore the cheaper the better.

    The materials provided by the university are: Steel/MDF for the body, 2 drills motors, 2 servos for speed control, controller and receiver.

    The only things not funded are the wheels and weapons. I was planning on buying rubber wheels (nothing too special because I can't see any of the other robots doing much damage).

    My question is what size ram would you recommend buying, it's doesn't have to be anything spectacular, just enough to flip a robot over or even slightly lift them off the ground.

    Another question I have is if I were to buy a 12oz paintball co2 cylinder what size buffer should I buy and roughly how many uses would I get out of it.

    Sorry for the essay I'm just very keen to get started, also sorry if these questions have been asked before! I'd appreciate any help or guidance any of you could give me.

    Thanks

  2. #2
    maddox10's Avatar
    Member

    Status
    Offline
    Posts
    2,296
    Post Thanks / Like
    Working pressure of the setup, and the wished for effect are 2 things I need to know before recommending a size.

    Also, it's the size of the ram that dictates the size of the buffertank, and the amount of flips/lifts you can get from a 12 oz bottle.

  3. #3
    bitternboy's Avatar
    Roboteer

    Status
    Offline
    Name
    Jonathan Atkinson
    Location
    Sheffield
    Posts
    31
    Post Thanks / Like
    How are you using the servos to perform speed control?
    Also, what uni are you at? I was chatting to a new module leader at Sheffield who wants to do something similar; I can point him in your uni's direction :P
    I'm aware I'm asking questions instead of giving answers, sorry

  4. #4
    Member

    Status
    Offline
    Name
    Jan
    Location
    Bad Oldesloe, Germany
    Posts
    94
    Post Thanks / Like
    Also, do the drill motors come with the gearbox? else you might have a problem there...

  5. #5
    Roboteer

    Status
    Offline
    Name
    Sam Betts
    Posts
    6
    Post Thanks / Like
    Hey everyone thanks for the quick response.

    @bitternboy

    For the speed control we will use 2 servos, one for each motor. They will mounted on a copper circuit board and be able to go 2 different speeds, full speed and half speed. Half speed is achieved by connecting 2 resistors (one for each side of the board). <- That's a rubbish description but I'll post a picture when its been built.

    I'm at Brighton University and the module is taught by Ian Watts if that's useful to you.

    No worries about asking questions, ask as many as you want!

    @Runsler

    Yes the drills do already have a gear box all I need to do is lock the clutch (I think so anyway).
    @maddox10

    I will say we would operate it at about 8 Bar. Does lower pressure mean less gas used (meaning more flips) or is that not how it works? For the size of the Ram I just want a small system, nothing large and expensive. Sorry for all of the questions but I really don't understand pneumatics very well (electronics student).

    @everyone

    Thanks
    Last edited by Yohooshi; 15th February 2017 at 09:54. Reason: Mistake

  6. #6
    bitternboy's Avatar
    Roboteer

    Status
    Offline
    Name
    Jonathan Atkinson
    Location
    Sheffield
    Posts
    31
    Post Thanks / Like
    For the speed control we will use 2 servos, one for each motor. They will mounted on a copper circuit board and be able to go 2 different speeds, full speed and half speed. Half speed is achieved by connecting 2 resistors (one for each side of the board). <- That's a rubbish description but I'll post a picture when its been built.

    I'm at Brighton University and the module is taught by Ian Watts if that's useful to you.
    Ah, gotcha, that sounds like a pretty fun build! Ad hoc micro-switch/servo speed control makes for quite a jerky driving style but you can probs get used to it.

    Thanks for the tip off, I'll pass it on

  7. #7
    RobotExtreme's Avatar
    Member

    Status
    Offline
    Name
    Guilherme Ferreira
    Robots
    Galactus, Rabid M8
    Location
    Lisbon
    Posts
    78
    Post Thanks / Like
    Hi Yohooshi,

    What you discribed is an Mechanical Speed Controller (MSC), many years ago used on RC models before what we now call ESC.

    http://radiocontrol.wikia.com/wiki/M..._speed_control

    I can´t not say that this type of application on a Fight robot is hazardous:

    -For be very fragile during combats.
    -Most important, if the mechanism "break/stop/stuck/battery disconect" at a "on" position you can´t control the robot moviment, what can result in accidents (I used this solution many years ago on weaponless Hobbyweight ). Same could happen with a ESC, but its a LOT harder to happen. Im not sure if anyone will not allow (even rules) you to compete with this system, its just an advise.

    Guilherme

  8. #8
    lowndsy's Avatar
    Astronaut

    Status
    Offline
    Name
    Steve Lownds
    Robots
    Flat Damon (FW)
    Location
    Derbyshire
    Posts
    129
    Post Thanks / Like
    Was it Gemini back in the old days which used a servo to control the joystick of an electric wheelchair?

  9. #9
    Member

    Status
    Offline
    Name
    Jan
    Location
    Bad Oldesloe, Germany
    Posts
    94
    Post Thanks / Like
    As far as i understand, you'll only use the bot for "intern" combat, meaning just you and other students in the same module, right?
    So i wouldn't care too much about safety rules or jerky drive style, since all competitors will have that (and it seems mandatory, so... no use in switching it vs. a somewhat expensive esc, and getting an unfair advantage, i think )

    Only three considerations that could be done from that:
    1. Mention that nowadays standart would be an esc, and the safety issue. could be your prof changes his mind due to that, making you use an ESC instead of MSC. But i think this solution was choosen mostly on budget questions or because they already lay somewhere in the university.

    2. build a bot that doesn't need too fine driving. (So... a horizontal spinner for example), or choose wheel size (and therefore speed) rather a bit smaller (so slower) if aiming is more important than actual speed (for example in a vertical spinner).
    Will drive a bit like steering any race games with a keyboard... many small tips on the keys to make wide curves.

    3. With the MSC being rather fragile, a strong flip could be devasting. If you can aim right, and won't flip into nothing, with the recoil destroying your own bot



    And for the pneumatic stuff... i never got into pneumatics, but:
    "pressure" of a gas can be seen as how many gas atoms are in a given volume. (well, kinda.)
    So if you have a given amount of atoms in the gas tank, and you operate a system with a higher pressure, you are very likely to blow out more atoms at once, making the tank last a shorter time.
    But Pressure alone isn't the only thing to consider when trying to build something "powerful".
    Pressure is just force per area (is my english right here?) -> p=F/A -> F=p*A
    So you'd want a lot of force to flip the other bot. Building up a high pressure is one thing, but increasing the size of your system, mainly the area the pressure works against also increases the force you get out of it.

    And since weight is always the biggest struggle:
    someone actually used that for a bot should explain what size/weight ratio of all the parts needed is most efficient.

    Also, as always, leverage is important. so how far from your hinge will your gas system apply its force, and how far from the hinge will the enemy bot be at maximum?
    Last edited by Runsler; 15th February 2017 at 13:51.

  10. #10
    maddox10's Avatar
    Member

    Status
    Offline
    Posts
    2,296
    Post Thanks / Like
    Hi Yohooshi,

    Lower working pressure means bigger rams to do the job you want to do with them. Bigger means heavier, even if the materials used can be build lighter in themselfs.

    Advantage of 8 bar is that you can source commercial parts. Brands, Festo, SMC, Norgren, Metalworks or even "el cheapo chinese".

    In the end , the gas in the bottle can be compared with electrons in a battery.
    The more work you want to do in a certain time, the faster both will be discharged.

Register To Comment

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •