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Thread: New Mech: Nostromo

  1. New Mech: Nostromo

    Hi all; I've been lurking here for a while and posted a few things but now that my project is seriously underway I figured I'd create a build thread for it. I'll just update this thread as I go with new posts per day of progress. One request - I know I'm not doing some of this the ways others have done it. Please refrain from beating me up too much because I'm not conforming to the traditional approach. If I fail then this will serve as a good object lesson. It's my failure to make after all, not some grumpy person who doesn't like people trying things out of the norm. Basically, nay-saying would be bad though constructive criticism and feedback would be greatly appreciated.

    Overview
    I'm making a custom chassis'd quadruped mech with dual airsoft guns. The mech will be used in three competitions at RoboGames: Defcon, Mech Warfare (Airsoft), and Mech Warfare (Hardcore). It needs to be working in some form by March 6th as I want to take it to the "Central Illinois Robotics Bot Brawl" to get a feel for how these competitions go and see how it works against other mechs and what to improve before RoboGames. This imposes a 24" height limit otherwise I can't use their portable arena. Seems a good restriction either way.

    General Design Concept
    In some ways my mech is very different than the norm and in others it's quite basic and traditional. From the beginning, I've been reading about how weight is always a concern in mechs and that most of them really have trouble holding up the needed equipment so everyone has to go with ultra-light guns or super expensive servos or a combination of each. Because of that, I've decided to not use servos at all. I'll be using a couple of different types of stepper motors and totally custom mechanical linkage for them. Think linear actuators and gearing with limit switches. The overall design is such that weight won't be as much of a concern. This gives me freedom on guns and batteries I wouldn't have otherwise. Overall I'm focusing on stability of the shooting platform, accuracy of the guns, and rate of fire.

    Walking
    I've no way to catch up with all of you gait/IK experts and I'm not going to spend the money to buy super expensive servos so I'm not even going to try. My mech will be quite a bit slower than most of the mechs in the competition. I'm using two DOF legs; vertical and forward/backward. I'll use the creeping gait that you see sometimes so three legs are always on the ground and the COG is between them. I'd like to use IK but I don't think I'll get it working effectively in time, we'll see. The legs themselves are locked in a 90 degree angle to the floor and to the body. The feet will lift up vertically using the actuators. The current design has the legs being fairly long so the movement speed shouldn't be too bad.

    Brains and Communication
    I've got an Axon II that came in the mail yesterday and I'm already playing with it. This will be the on board brains of the robot. I'll be using the ubiquitous XBee system to handle communication with the mech from my laptop. The Axon II looks great with it's huge number of inputs/outputs and 4 UARTs, etc. Seems like it should work great for this project as I need two outputs per stepper motor. I plan on it really just controlling hardware based on commands sent from the computer so it won't be doing a lot of heavy lifting or logic. I'd rather use a true on board computer but I'm trying to keep the electronics (my weakest area) simple to avoid problems.

    Camera and Vision
    I'm going to go with what the consensus says works: the Trendnet wireless camera. This seems easy enough. The camera will be mounted dead center of the mech on the same turret mechanism that houses the guns and rockets. I'm going to be doing a bit with fiduciaries and CV if I have time so the bot can track the target panels on it's own but this is secondary and might not make the cut.

    Turret
    Since I'm going for slow and steady in the walking, I expect to be competing against other mechs that are faster than mine. I've watched every video of every mech I can find to understand as much as possible of the challenges in this competition. To that end, my turret has a few requirements that my design has to meet.
    • ~400 degree horizontal rotation (azimuth?) since my mech will turn very slowly
    • ~110 degree vertical rotation (elevation) so I can shoot at my mech's feet and hit taller mechs
    • Fast and repeatable rotation. I need to be able to quickly move to a specific spot consistently
    • Stable and recoil free. Between guns, rockets, and camera, the turret will have a bit of weight on it. Additionally, it's critical the recoil doesn't cause the camera to jitter all over the place. Rather than trying to come up with a recoil dampener, I'm just going to make the turret steady as a rock and hard mount everything. This won't eliminate recoil, but it will minimize it. It helps that I use aluminum for everything and I can custom machine 3d parts as needed with my CNC mill.


    Guns and Rockets
    This is where I take a radical departure from the norm. I'm not using tank guns or cheap plastic airsoft guns. I'm using two metal gearbox automatic electric pistols and running them at 12v. The guns are mounted to the sides of the turret with the rockets in the same assembly. The camera is in the center of the turret. At 12v, each of the guns is firing about 15 rounds per second, maybe a touch more, it's hard to tell. So the total rate of fire is 30 rounds per second between the pair. I've turned down the velocity of the BBs a bit so they won't be dangerous - they should be right around 200 FPS, pretty mild for airsoft. Before anyone says so, I know you can only score 1 hit per second but as best I can tell most of the hits were more luck than accuracy or consistency in last years competition. I feel that focusing on the weapons portion of a mech rather than the movement is still fully valid within the rules and a legitimate approach to the competition, both in spirit and in practice.

    It's not really effective for gravity feed to push this many rounds so I'm using a motorized tube feed system invented by a guy that makes airsoft machine guns and needed to support the equivalent of a belt feed ammo drive. It's a pretty simple design and I've got it working already. This lets me haul a few thousand rounds of ammunition on the mech. The ammo can be stored anywhere on the mech as the feed system is capable of pushing it several feet up and around corners, etc. I've not quite figured out where I want it to go. Each gun is fed independently but I think I'll use a single hopper with two feeders in it.

    The rockets themselves will likely have the same mechanism used for firing at last years competition by Squidword. It's a solid design that I really liked. I don't have their physical layout designed yet so I'm not sure the number of rockets on the mech. I'd like to get fins and such on em but I can't quite come up with a design I like that looks good.

    Control System
    The mech will be remotely controlled from my laptop. I will have custom Java or C# software on the computer to handle actual display of the video feed as well as the actual control of the bot. I expect I'll use a more "video game" control approach than I've seen others use. Something like WSAD keys for moving the mech - forward/backward, rotate left/right. Then I'll use a "drift towards target" type of targeting system you used to see in the old space fighter sim games - Privateer for instance. Basically you move the target hairs on the screen where you want to go and the system moves the guns/camera towards them - basically the system and you are always correcting towards the target. It's both intuitive and quite effective.

    Since the turret has such huge range, there are a few tricks I'll need to add to the software - like reversing and rotating around the other direction once it's limit is reached and detected via limit switch. I also want the UI to show the mechs orientation in relation to the turret and have some feedback loops on things like it it's firing, taking damage (and from what side), etc. Since I'm a video game programmer by profession, I'm looking forward to making a cool control system if time permits and all the mechanics work.

    Summary
    Whew, long post but I'm kinda proud of the work and research I've done so I like to talk about it. Sorry about that. In short, Nostromo will be ugly, slow, ungainly, and capable of raining a hail of BBs down on it's target fast and consistently.

    Have fun!

    -Mike

  2. Re: New Mech: Nostromo

    December 19th, 2009 Status
    As of today, I've recieved the vast majority of the initial set of parts and will start working in CAD in earnest. I'll have at least a couple CAD diagrams and photographs to post sometime today.

    Design - the design is significantly done on paper. Most of the major components are at least partially fleshed out with the complex areas complete. Starting today I'm going to be creating CAD models for all the components like the camera and the axon so I can really get the design down with scale. At first I thought the bot would be big, but most of the components are pretty small so I think it's going to be a little bit smaller than I expected. That makes it much easier for me to mill parts for it - less fixture creation needed.

    Brains - My Axon II is on my desk and I started playing with it last night. Looks pretty solid and a very nice piece of electronics kit. AVRStudio gave me a headache compiling because it's still not really Vista 64bit compatible. The problem was in WinAVR specifically but I got it sorted out in the end. Now I just need to learn the API ins and outs. Fortunately programming is programming and once you know enough languages it's pretty easy to pick up new ones.

    Steppers - I've a huge pile of salvaged stepper motors from three printers and one scanner in front of me. I also have two specific motors from Jameco as well. I don't plan on mixing/matching motors for a given task (all vertical leg motors will be the same, all hip the same, etc) but I'm using the pile to come up with what will work best for each use without buying a mess of motors. I also have two very nice EasyDriver stepper boards here as well. I'll be using them to control all the motor goodness.

    Ammo Drive - I have all but a single component for the ammo drives here and I've already modified the servos and magazines to do what's needed.

    Guns - I have both of my airsoft guns stripped down so I can run them without any internal electronics. I've already removed all unnecessary mechanics like the trigger assembly and such. Test firing those buggers off some car batteries was fun. They are surprisingly loud when you expose the guts. Building the replacement frame is going to be one of the harder parts of the whole project as they are using tiny pins to hold everything in position and I don't know how to measure it accurately enough. I expect I'll use the DRO to jog into position, note it, jog to the next position, note it and then see how it goes in a few test pieces of wood. I prototype everything in 2x4's on the mill because it's so cheap and cuts reasonably well for rough stuff.

    Anyways, back to work for me!

    -Mike

  3. #3
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    Re: New Mech: Nostromo

    Sounds fantastic!
    I Void Warranties�

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    Re: New Mech: Nostromo

    You don't know how much I love all of these scratch built bots! I can't wait to see it all come together.

    I'm also really impressed with the fact that you are using salvaged stepper motors. you only need 2 outputs to control them? I can't wait to see you moving them around. I think a lot of us could benefit from what you learn. Controlling stepper motors with an axon...would be cool. Be sure to post a tutorial on how to do it once you have it all locked down.

    One thing about a high firing rate...With the cheep plastic guns, they tend to swing around all over the place after the first shot which creates a wall of BBs that can be near impossible to get around. If you have a relatively mobile turret, then you may be able to gain a good position and pin down the other bots. Here is where two on two matches will be fun.

    Again, keep us all in the loop, and post pics and videos of your progress.

    DB

  5. #5
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    Re: New Mech: Nostromo

    Mount-up a couple of these bad boys: http://www.airsoftgi.com/product_inf...oducts_id=4514 and the 'bot would be a guaranteed winner!
    I Void Warranties�

  6. #6

    Re: New Mech: Nostromo

    This sounds like a really cool project. You're making me think of all the old printers I tossed in the garbage over the years...

    It's not really effective for gravity feed to push this many rounds so I'm using a motorized tube feed system invented by a guy that makes airsoft machine guns and needed to support the equivalent of a belt feed ammo drive.
    Do you have any links to this information?

  7. #7
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    Re: New Mech: Nostromo

    The steppers in an average dot matrix or ink-jet tend to be MD2s. They're good for just over 40oz-in of torque.
    I Void Warranties�

  8. Re: New Mech: Nostromo

    I'm going to be creating CAD models for all the components like the camera and the axon
    Which CAD software are you using? Send over the final design and I'll post it up for others to download.

  9. #9
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    Re: New Mech: Nostromo

    Or he could just post it here. Over in the Datacenter section...
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  10. Re: New Mech: Nostromo

    Well, as long as I'm aware of it so I can link it directly to the Axon II site.

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