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Scratch Build – In Progress Robotic Argo: Computer control time

Discussion in 'Project Logs' started by theevilelephant, 3 Dec 2009.

  1. theevilelephant

    theevilelephant Minimodder

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    This is something I've been meaning to start writing up for quite a while now. It isn't a computer case mod but it involves computers and modding, plus I hope some of you may find it quite interesting. (If this is in the wrong section, sorry, please move it where it should be)

    So time for a quick intro! I work at Aberystwyth University in the robotics department, this will be a project log type affair focusing on one of the robots that takes up a large amount of my time right now, be warned I may wander off topic to other robots I'm also working on, I apologize in advance. The end goal is an autonomous robotics platform, which will carry a whole load of sensors do interesting stuff! Nice and open ended which is great.

    So lets get started, we could have started from scratch building everything ourselves, but while we can fabricate most things pretty well we opted to start with one of these:
    [​IMG]

    Its an Argo Frontier 6 wheeled amphibious vehicle. It has a Briggs and Stratton 23hp petrol engine and does something like 24mph tops. The reason for choosing it as a starting point is that it's well made, waterproof and, relatively, cheap. The end goal is a fully autonomous robot, but that is a fair way away.

    Before I go on with the robot, I'll show you what I have to work with
    [​IMG]
    [​IMG]
    (sorry for the poor quality photos my phone camera is rubbish and I haven't had a chance to take some nice pictures with my DSLR).

    Thats one of our robot labs, we have two pillar drills (one large and one small), two big lathes, a milling machine, bandsaws, compressors and what seems like an infinite amount of small tools although I can still never find what I need! Its constantly full of robots needing fixing, making, breaking and everything in between and is generally a complete tip :( We also have another "nicer" lab which has a vicon tracking system, lots of PCs and a whole bunch of other stuff.

    It currently looking more like:
    [​IMG]
    Bits of big robot boats.
    [​IMG]
    Various robot boats, helicopters and random bits of kit.
    [​IMG]
    An argo (which is now somewhere in new zealand laser scanning river beds) and yes, thats a gwiz in the corner.

    So thats my introduction, as the log has to catch up with the current status of the robot( :blush: ), I will try and put up a few more updates in the very near future.
     
    Last edited: 25 Jan 2010
  2. stonedsurd

    stonedsurd Is a cackling Yuletide Belgian

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    Hahahaha Reva! :hehe:

    Nice idea, I'm subscribing.
     
  3. Validus

    Validus What's a Dremel?

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    I'm super pumped to read about this! Good luck to you on this project!
     
  4. Cheapskate

    Cheapskate Insane? or just stupid?

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    Please let there be a shotgun!Please let there be a shotgun!Please let there be a shotgun!Please let there be a shotgun!Please let there be a shotgun!:hehe:

    I'm sooo going to watch for this thread! Should I be amused that the Argo is bigger than the car?
     
  5. Jipa

    Jipa Avoiding the "I guess.." since 2004

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    A six-wheeled autonomous thing will be scary as hell. I love it! Just please have lots of emergency stop-buttons all over it, just in case it gets a bit too clever.
     
  6. theevilelephant

    theevilelephant Minimodder

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    Lol H&S people have enough problems with it, if we put a shotgun on it I'd probably spend my life filling out forms! The Argo is indeed bigger than a Gwiz, although it's not as heavy.

    Time for another update. So the first problem on the list is a relatively simple one. We need to be able to control the throttle. Now most robots are driven by electric motors which are nice and easy to control using PWM (pulse width modulation). For example:
    [​IMG]
    which is one of our other robots.

    Sadly this being a petrol engine it's not so simple. The solution we came up with after trying few others is basically a high torque servo connected to the throttle control:
    [​IMG]
    Mounted with a stunning piece of engineering (if I say so myself) involving some expanding foam and some zip ties.
    [​IMG]
    Using a simple aluminum connector and brass lever. The wire holding it together was meant to be temporary but it's thick enough gauge to hold the pieces together but flexible enough that should something jam, the servo doesn't rip itself to bits!
    [​IMG]
    Side view of the assembly.

    The reason for a high torque servo (a Futaba S3306) is that as the engine revs up the governor tries to push back on the throttle control to try and regulate the speed somewhat. It even manages to push back that servo occasionally, which even if I try my hardest I can't even move!

    After bolting the air-box back on, I gave it a quick test and it seems to work fine! Yay!

    Next up -> steering.
     
    Last edited: 4 Dec 2009
  7. bigsharn

    bigsharn Officially demotivated

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    This looks like a hell of a project...

    Subb'd
     
  8. theevilelephant

    theevilelephant Minimodder

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    The planned emergency stop button is going to be a remote ignition shutoff (which also means you can start it remotely :D ). The software is going to be/being written by a final year MEng student, which can sometimes mean it won't be great due to the huge amount paperwork they have to do as well. Luckily for us the guy doing it seems to be awesome so I'm sure it will be great and not kill anyone :rolleyes:
     
    jhanlon303 likes this.
  9. jhanlon303

    jhanlon303 The Keeper of History

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    I have to give you rep just for the sheer awesomeness of your toys. I will watch this one!

    john
     
  10. Jipa

    Jipa Avoiding the "I guess.." since 2004

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    Oh btw any more info on the robots you've already built? The one in the picture looks pretty interesting. Still lacks the shotgun, though :(
     
  11. Cheapskate

    Cheapskate Insane? or just stupid?

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    Ok... It doesn't have to be a shotgun... Have some inspiration. - Just kidding.
    I'm hoping the foam mount on the engine is temporary. I think they will fail you if you use duct tape too.:D
     
  12. theevilelephant

    theevilelephant Minimodder

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    The foam is really there to keep the servo in position whilst also allowing it to move a bit. Basically servos are cheap (relatively) the Argo isn't I'd rather the servo broke than the Argo! If it was bolted on really solidly then every time the governor "kicked" back at the servo, the servo would gradually rip itself to bits. I'm sure we will come up with a better solution at some point, probably involving bolts and rubber mountings.

    I haven't built many as I'm new to the department (read undergrad working there for a year long industrial placement), but I can tell you about the other robots we have/work on.

    [​IMG]
    - Idris - a 400kg, 4-wheel drive electrically powered robot. It can have a variety of sensors on top, usually a gimbaled panoramic camera (sometimes a robotic arm or a laser scanner or a combination), its usually used primarily for robotics vision research.

    [​IMG]
    - Beagle - 4m long custom built robotic boat with a carbon fibre wing sail. It has GPS, Sat comms, electronic tilt compensated compass, wind sensors and a bunch of solar panels.

    We also have shed loads of smaller boats about 70cm long and 2 about 1.5m long.

    The primary focus on all of the boat related stuff is oceanographic research (water quality sampling/monitoring).

    [​IMG]
    - Fancy robotic arm - basically a 7 DOF (degree of freedom) manipulator with 3 fingers (another 7 DOF), each finger has 2 tactile sensors. It uses a pan/tilt stereo camera setup as its "vision". Used for research involving teaching the arm to pick things up (relation between vision and manipulation).

    [​IMG]
    - EXO Mars Rover - does it really any explanation?

    [​IMG]
    - Pioneers - simple off the shelf robot platforms for developing stuff in the lab/student practicals. We have about 9 of them (all named after Simpson characters :D ).

    There are more but those are the main ones, the latest additions are two Argos, three Gwizs and two RC helicopters.
     
  13. theevilelephant

    theevilelephant Minimodder

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    A quick note: I now hate opera I wrote out this whole post once and it refreshed the page :grr:

    Right so next up steering. As we wanted to Argo to be still be human drivable (or easily/quickly made human drivable) we decided the best way to go was a linear actuator bolted to the the handlebars. This means we can jsut pull out a pin/bolt from the handlebars and we can steer manually again. The actuator is an LA12 linear actuator from linak. It has a 100mm stroke and can apply up to 700N of force.
    As the Argo is skid steer we will need all of that force. Basically as you turn the handlebars you apply the brakes to one set (side) of wheels, allowing you to skid around them. However it requires a hefty amount of force to push the handlebars hard over (which gives you the best turn).

    So the first job is to mount the actuator, however it is attached needs to allow it move in most axis to stop the actuator from bending.

    [​IMG]
    A bit of machining later and there we have it, it ain't pretty but it works.

    [​IMG]
    Top view

    While I was at it I quickly machined a small tab of steel to help reinforce the end of the actuator.
    [​IMG]
    Roughly milled/hacksawed.

    [​IMG]
    Test fitted, a bit long but that can be fixed!

    [​IMG]
    Drilled, filed and mounted.

    [​IMG]
    Finished assembly.

    So now we can control the throttle and the steering it's time for a test! The quickest way to do that is with a few bits of RC gear.

    [​IMG]
    Did someone say cable management? Hacked together 2 channel reciever, motor controller and hastily made vero-board power regulator board.

    [​IMG]
    All of which is powered by this.

    [​IMG]
    And controlled by this!

    And there we have it, a 400kg, 6-wheeled, amphibious, remote controlled toy!

    I will put up a video as soon as I find it!

    Update:
     
    Last edited: 8 Dec 2009
  14. bigsharn

    bigsharn Officially demotivated

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    I want it so badly :(

    I actually never thought argos could skid like that, I assumed they worked the same as tracked vehicles :p Just out of interest what's powering the on-board equipment? I know it'll need to be a diesel generator or a dozen batteries or something, and do you think will it slow it down by much?

    Either way, nice work so far :)
     
  15. theevilelephant

    theevilelephant Minimodder

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    At the moment it's just being powered by the battery (normal car battery) eventually it will be powered by two 12v leisure batteries in parallel. They can run a normal pc for quite a long time :) haven't tested how long yet though. The extra weight won't really slow it down because the weight of the batteries + pc is less than the weight of the person that won't be in it , if you see what I mean lol
     
  16. theevilelephant

    theevilelephant Minimodder

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    So time for an update, not managed to get a huge amount of work done on the project over the Christmas period, been busy with loads of other projects.

    So a bit of catching up to do!

    Presents from the postie, two wireless frequency analyzers, which I expected, and what appears to be upon closer inspection a can of geraniums....
    [​IMG]

    A present from... well the god of bloody annoying.
    [​IMG]
    RC Helicopter + strong gust of wind = tangled counter rotating blades and a 30ft fall into a greenhouse.

    Anyway on with the ARGO, now that we have the mechanical means to control the ARGO (as proved by the RC test), its time to replace the RC gear with a computer and start getting this thing autonomous. In our case the computer is actually a combination of things, a PIC18f and a gumstix. The are both mounted on a custom made board along with a compass, gyro, gsm module and gps module.
    [​IMG]

    The PIC deals with reading pot/sensor values and setting throttle speeds/steering angles, the gumstix runs an actual OS which means network support so we can control it via laptop and get some data from the robot as it's running.

    Here is the board in position it is connected to a motor controller (for the steering actuator) and a servo controller for the throttle servo.
    [​IMG]

    Now that the robot will not be directly controlled by us, time for some safety. In this case a remote switch-box wired up to the ignition. Yes that does mean we can START the ignition remotely as well as kill it :D
    [​IMG]

    Nicely mounted up
    [​IMG]

    That's it for today.
     
  17. Picarro

    Picarro What's a Dremel?

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    Where is your lab located? And what are the frequincies used to control the automatic ignition and steering? ;)
     
  18. MarkW7

    MarkW7 Total Noob

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    This looks pretty interesting, subbed, :thumb:
     
  19. Cheapskate

    Cheapskate Insane? or just stupid?

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    Do you ever get sick of all of us whispering 'rampage' while you work? :naughty:
    +Rep if you set the laptop up to play random one-liners from the Terminator movies.

    The foam + hot motor still bugs me. Everything else is brilliant.
     
  20. Shadow703793

    Shadow703793 What's a Dremel?

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