Attempting to build an ATAT

VEX V5 General Discussion General Forum
21

Currently? Nothing. I’m still thinking on that; I’m starting to like the single-channel dual receivers the most.

However, I’m not sure if the legs can handle much more weight. Any tips for lightening up the structure? I want to be able to put a small head on it, possibly with an ultrasonic sensor mounted on or behind the head, to serve as a rangefinder. Right now, though, I’m a little leery of adding more metal; that’s why the ATST didn’t work as well as I had anticipated.

I do have to admit: it is one fat ATAT.

22

Be careful of the microctroller placement - you might not have room to squeeze a battery in the rear one.

23

I checked that as soon as I saw your post; surprisingly, both batteries fit into the controllers quite well. They’re mounted horizontally lengthwise along the underside of the chassis down the center pair of rails.

You are right, too: it takes a tiny bit of work to get the battery connector into the rear microcontroller, squeezing it between the two, but the work is mainly positioning the connector in just the right way that it slides right in.

24

Are you building with the Aluminum Plates??? That will help a lot… You could always try to build your own Legs, out of Plastic…

25

Hey Steph, I’m looking at the robot right now, and (gosh it’s heavy) I would swap the 24-tooth sprockets on the upper leg motor shafts with 10-tooth ones, so you can gear the legs down (the ATAT is so heavy that your motors are sagging quite a lot, which would require some annoying programming to fix; it also might be going too fast at 7:1). Don’t swap all the 24-tooth gears, just the ones on the motor.

John

26

For now, until I find out whether or not I can order aluminum parts or machine my own, I’m just gonna put some ‘training wheels’ on it and change out those sprockets.

When I got in this morning to work on it (I’m an intern, this is my project) it looked like a dead bug, like someone had pressed down on the top until it collapsed. Not sure what happened, but the motors might have given out or something, although they seem to be working fine right now. Prob’ly the weight issue. I’ll look into it, but hopefully the training wheels will help…

27

If you have the budget for having something made, you might look at Plastic, of some sort…

Well, there are “worse jobs” for the Summer… :wink: The Motors might have slipped, because of the Weight… Best of Luck, and ask questions (here) if you need some help, someone might have some knowledge about the issue…

28

OOOOOOkay. I’m going to take a deep breath…

So, I plugged it into the remote to test how long it took one of the primary hip joints to raise and lower. And it couldn’t stay up. Would replacing the motor with a servo work? I read somewhere that they can hold a commanded position, but does that apply to the VEX servos? When I took one apart a few years ago, the only difference I could spot was a key inside one of the gears that prevented rotation past 180 degrees.

And I have no idea where to start with the programming. But I do remember that on some motors, they turn slightly slower in one direction than the other, so would limit switches help counteract the time difference? Or should I just change the amount of seconds?

29

Sorry for the double-post guys, but I’ve got some good news; I figured out the code issues, and I’m now working on a test sequence.

I had a bit of a thought earlier; since the knees would actually get in the way in this design by flopping around, would it hamper anything if I just used some long rails for a straight leg and just made the ankle a joint instead of fixed?

30

You might want to investigate a double bar linkage. Here’s a terrible sketch:

[Robot Body]
    /  /
   /  /
  /  /
 /  /
##### (foot)

becomes:

[Robot Body]
    \  \
     \  \
      \  \
       \  \
       #####

With a double bar linkage, the feet will always stay flat relative to the ground, no matter what angle the legs are at.

31

How do I put up a video? I just got a video of the robot testing out its motors for the first time and it looks great. And it has new legs.

32

Videos are not one of the Approved File Extensions. You could place it in a Zip File, but there is a 3MB Max Size. You also have a MAX LIMIT for uploads here at Vexforum… You might need to upload to YouTube or other Video Sharing site, or Host it yourself…

33

And here’s the video:
http://img65.imageshack.us/flvplayer.swf?f=Pmvi1779

Took me a while to get it working, but there it is.

34

The Video, or the Robot???

35

Both, actually… This robot has been on the itinerary for me for about two weeks, maybe even two and a half now.

36

The leg motion is great!!! Is the next step to “teach it to walk”??

37

Yep, but that’s probably going to take longer. I’ll need to code in optical shaft encoders so the robot knows where its legs are at all times, so that it can start from pretty much any position. Correction; this will definitely take longer. But I’m glad I’ve finally had some success.

38

From the way the legs work, you should be able to use potentiometers, which are smaller and more accurate for this kind of purpose. I look forward to more status reports.

39

It appears that you have some Supports in the Middle… Because of the Strength of the Motors/Servos and the Weight of the Materials, you might no be able to get away from that, but over all, that is Very Cool!!! Shoot some good Video…

For motion of your ATAT, The Center of Gravity will need to shifted to the Legs not in Motion, to move the other Legs forward… Remember that 4 Leged Animals, move the Left Front/Right Rear Legs at the same time, and then the Right Front/Left Rear at the same time.

Thinking about ATAT’s in Star Wars 5, In a CGI world, Gravity does not need to be obeyed, just Virtualized.

40

There are mechanical ATATs that walk with the left-left-right-right gait, but I’m thinking of using the left-right-left-right gait for this one mainly for stability. I’ll see if I can write code for both; if the one that’s used in the movies works, I’ll go with that, but I’d be happy if it moves at all.

As soon as it’s done being programmed, I’m going to test the walk cycle and see if I can remove the supports underneath. They’re set up so that the robot can walk with them, but I hope to be able to program the legs to work without them.