Vex IED Final Project: Conclusion

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So we’re done. We competed and did exceptionally. We won, beating second place by more than a factor of two in total points. However, we pulled out of the competition after our last match to ensure that as many high school teams as possible walked away with hardware; despite this we were given a trophy privately later. In short, I think we did alright.

Here’s the final robot specs and a nice little summary of what we could do:

Cool perspective shot!

Cool perspective shot!

First, our drive base. One Vex motor per side, directly driving the tank treads. This was pretty slow on the ground to say the least, but it made the drive very reliable and compact, which was more important for us than overall speed. Our original intention was to use the Motor 393s with their high speed gearing; this would get us a competitive speed without sacrificing the benefits of a direct drive. However, we ordered the wrong motors and got the still-great Motor 269s instead. We ultimately were about as limited by our drive base as our arm speed.

The tank treads were able to climb the stairs once they balanced on the corner of the first step. An idler sprocket was placed about 2 inches from the end sprocket and dropped 1/2″ lower. This made turning easier and helped with high-centering on the electronics board. It also gave us an unintentional “feature”: we could extend our arm to push our CG far enough forward to “rock” onto very short sections of tread, for enhanced turning ability.

The arm had a 25:1 shoulder joint and 7:1 wrist joint, carefully calculated to do all of the work needed. The shoulder joint was powerful enough to lift the entire robot; we used this to get up the stairs by pushing the arm against the second step. This torque was also enough to self right the robot. The wrist joint articulated our claw for grabbing various objects at different angles. Our gripper was a simple Vexplorer claw Рit adequately gripped everything, so we moved on to different subsystems. In review, we probably could have done better with a roller claw designed to pick up all of the game objects that happened to have the same width.

All of this together made for a winning robot. For more info on our design process, there are many earlier posts on it; I’ve been meaning to make an “IED category” soon, but never get to it.

Here are our match videos: Match 1 Match 2 Match 3

I’m rather proud of the result as it was quite the excellent robot. I’ve never dominated a competition before, and it’s certainly a pleasant experience.

Shaker Robotics Public Build 2011

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So here’s the announcement / non announcement: We’ll essentially be posting almost everything we do to this blog during build. Not much of a shock, I know…

Funny thing: I didn’t actually intend that other post to be an announcement of our intention, as I kind of sort of forgot to do something most teammates do when speaking on behalf of a team. You know, little details like “show up to meetings” and “ask the leadership of the team if it’s okay”. However, you guys ran with it, and people on the team seem to think it’s okay. I guess I know Shaker Robotics better than I thought. ūüėõ

We’re in a bit of “unique” situation this year. Due to budget cuts, our most dedicated mentor is only working part time. None of the other teachers have the ability to commit to meeting time like he did in 2009 and 2010, so as a result we’re working on lower in-shop hours. Tentatively, that’s 2 hours a day, 5 days a week. As a team, we plan to¬†compensate¬†with the Internet. We’ll be doing a lot of remote CAD design and discussions online so that we can use our in shop time optimally. If you want more “raw” information on our design process and some of the discussions our team has, we’ll be talking on our team forums. Right now they’re a bit of a barren wasteland where I spend too much time talking to myself, but they’ll pick up in activity with time. I think. Posting is restricted so we don’t have to fight off spam, but you can always leave comments on this blog.

The other thing worth noting is that I’m a full time college student. A struggling full time college student who is also part of the leadership of student government and a 10,000 watt radio station. After the first two weeks of build, I will probably be in no more than once a week. Posts will probably be made by proxy, or weekly. A nice side effect of this blog is that it will keep me in the loop during the build season, which was a very big challenge for me last year. Luckily, since I’m not actually that helpful of a team member the team won’t notice much of a drop off… but this blog might be less interesting.

Vex IED Project: Motor Mixups and 269 review

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Not much has happened that’s exciting on the IED project. The robot’s pretty much just been working. We added 1/2″ of drop in our treads to make turning easier and more importantly to make bump climbing possible with the location of our electronics. A second arm motor was added because the first motor alone was right on the edge of specification and a second motor made the system work better in unideal conditions.

However, our robot was somewhat counting on getting some high strength motors from Vex. We needed a direct drive drivetrain for size and space reasons, but we wanted to run faster than the piddle speed direct driving a tank tread sprocket gets you. Our plan was to get two Vex Motor 393s and run the high speed gearing. However, due to a mix up we received the Motor 269s instead, which are essentially the same specifications as the old 3-wire motors. Initially, I was¬†disappointed¬†and thought the motor change was pointless. After installing them, though, I’m really won over by some of the new features that make the motor perform a lot better.

First, the clutch is gone and metal gears are installed. This is really a lot nicer than you think. The clutches had their share of problems and often would strip or desync or get crooked. Plus, the plastic gears still found a way to shatter anyway, so they didn’t really serve their purpose. A shaft adapter is included to let you drop-in replace the motors with your 3-wires, but we didn’t use them. Our shafts were already about .66 inches too long so the removal of the clutch actually made the implementation perfect. Also attributable to the lack of a clutch: there is so much less slop in the drivetrain now. It’s great.

Second was a very small change to the Vex motors that really shows IFI’s attention to detail in design. In the motors they switched the side that the motor power wires come out of. This is awesome. Before, it was very difficult to mount a motor on the very last hole of a standard Vex chassis, because very little clearance would exist between the motor and the metal siding. Now with the motor coming out the opposite side, this problem is eliminated. Also worth noting is that the vast majority of motors are mounted as low as possible (spinning section upwards) for CG reasons. This stops you from having to wrap the motor wire around the motor. Overall, a tiny change that makes every application that much easier.

The motor with a controller is the same price as the old 3-wire motors, which is really nice, since the motor controller is essentially a free 1-foot extension cable. The previous motors had very short cords and virtually every motor had to be extended. And if you don’t need it, VEX ships you a zip tie with every Motor Controller 29. How thoughtful is that?

The only problem the motor seems to have is that the distinct “motor whine” is a different, louder sound. It’s a lot less “electronic hum” and a lot more “DESTROY DESTROY”. But that’s not a serious problem at all.

Using these motors has basically converted me. I’m going to replace every motor I own with these (and four 393s of course), they’re just fantastic.

EDIT: I got a PM today letting me know that the “motor whine” isn’t actually normal operation, but that my joysticks are decalibrated causing the motor to be sent a very small PWM command. Whoops! Thanks for the heads up.