Archive for January, 2011

Raiderbot X, 23 Days to Robot Ship: Lego Minibot!

Minibot proof of concept out of old Lego parts. The purple arms push against the pole, which angles the wheels into the pole to create a horizontal vector just strong enough to keep the bot on the pole. Took about two hours to make.

The bot is climbing up a 40 inch metal pole that is embedded in the concrete floor of our garage (for reasons beyond my imagination). Climb speed is about 6 in/s. Power is provided by a 13-year-old 9V Lego motor that is the wimpiest of the wimpiest Lego motors out there. It is being run on 12V.

The TETRIX motor we will be using in our actual minibot has 21.7 kg-cm of torque. This motor exerts no more than 200 g-cm of torque.

This is the first time in six or seven years I’ve put anything together with Legos. I think I’ve lost one of my tubs—I made this robot out of what few parts I could find. I need more gears!

Credits to my mother for taking the videos!

Raiderbot X, 26 Days to Robot Ship

This is an email I sent to the Raiderbot mailing list. I think it sums up everything that is going on.

Hello Raiderbot,

The bad news:

We are still a week behind largely due to delayed shipping of supplies and bad planning on my part. We have no driving robot, nor do we have a fully functional arm. If we add up all the hours, we have little over 60 hours (2.5 days) of work time left in the season. Also significant is the fact that too few people have been showing up.

The good news:

We have the aluminum tubing required for the chassis and have enough already cut for one chassis, ready to be welded using the jig constructed last week. HyTek has donated more plastic to us than we’ll ever need this year. We received the materials for the arm today and should be ready to start building tomorrow.

The roller claw beta prototype (demonstrated last week) looks very promising. Great job to everyone who helped design and fabricate it!

We have located a machine shop (Viper) that has the capabilities and is willing to manufacture our swerve modules (for the drive base). Spencer Hedrick is currently waiting to hear back from them regarding the cost and time of fabrication. We will know by Friday what the decision is. If the price is affordable, we hope to have the modules (and one robot) finished by the end of next week.

The scary stuff:

We need our first robot finished by the end of next week and our second robot by Wednesday of the following week. Please realize that although next week is only Week 4, it is already Week 4. It was our original plan to have the swerve modules finished first, but because the machine shops will not finish fabricating the swerve modules by the end of next week, we need to have everything else finished and nearly perfected by that time. This includes the:

  • Roller claw,
  • Four-bar linkage lifting mechanism (with milled aluminum tower),
  • Electronics board, and
  • The attachment of every necessary motor, sprocket, wire, belt, chain, pneumatic, and pulley we need on each of the two robots.

If all 46 members of our team meet and work consistently, this is entirely possible to accomplish in less than a week. At the current rate of attendance, however, this will not happen. Please also consider the fact that I haven’t even begun to describe what we need to do regarding the business plan, T-shirt design, battery cart, robot cart, scouting, pit build, pit panels design, minibot design, etc. There are too many jobs and too few people who come to meetings!

I am fairly happy about the attendance of the longer (Monday/Friday/Saturday) meetings; we got a lot done last weekend. However, attendance of the shorter meetings has been disappointing at best and unproductive at worst. Because we end two hours earlier, we need more people and dedication to maximize the use of our time in the shop.

It is our (me and Lipi) job as program managers to keep track of what resources we have to work with and keep the team on track for a successful season. Here, a “successful season” means we have completed the following (among other things) by Monday, 2/21, which is 26 days away:

  • 2 Robots
  • 2 Minibots
  • New website
  • Pit
  • Battery cart
  • Robot cart

The request:

We hope we are doing a decent job, but in being effective leaders, we depend on each of you. Regardless of your individual jobs, regardless of how small it is, regardless of how much it may or may not seem related to robots at all, everything you put into the team brings us closer to success.

We would like to go to every meeting knowing everyone will be there, but this has not been happening. We completely understand if you have other commitments (we do, too), but please let us know (by email, word of mouth, phone call) if you will not be there—then at least we can plan things accordingly so we aren’t caught short at the end.

Currently, the programming subteam is the only subteam that is (far) ahead of schedule. (Mechies, are you seriously going to let the proggies outdo you?) Congratulations. :)

Again, the roller claw is looking great. Please be there tomorrow to help finish building the arm and test it on the kitbot.

Cheers,

Lipi Gupta/Soo-Hyun Yoo

Tricopter: Accident Update

The shafts are a bit scratched up. I found that the prop savers had come a little loose, perhaps as a result of vibrations. I will need to apply loctite or at least check them before each flight.

The tail rotor must have cut into the tail ESC and the ESC leads as it ripped off. I will need to apply heat shrink or replace the wires.

I don’t know what I was thinking, but I had both the flight code and the joystick code assume an initial Z input of zero. Arming should be (and I knew this!) manual! This is problematic because the joystick has issues determining the initial Z axis value (reports it as 0 instead of -1). I must have nudged the joystick a bit, causing it to send an initial Z value of 0 even when it is not. In code, a Z value of -1 is minimum throttle, so 0 is actually mid-throttle. This is now fixed.

But at least it was mid-throttle. I don’t know if I could actually have even held my grip on the tricopter if it had gone to full throttle (as it had many times during testing).

Tricopter: Now in Five Broken Pieces

Curse my impatience.

I got wired control pretty much working, so I went ahead and hooked up my XBees (wireless link) for testing. I had my hand on the chassis just in case, but I guess I didn’t apply enough pressure—it went full throttle on its own (I had barely touched the joystick) and flew off the counter. In two seconds, the tail rotor ripped through my sweatpants and scraped my calf, hit the chair, broke free of its axle and ricocheted into a corner (I spent a good 10 minutes trying to find the detached rotor piece). Somehow, I got three cuts on my left hand, and the acceleration was such that it snapped the chassis into four pieces. Granted, the chassis was made of scrap PCBs, but it was double-layered! All three propellers are shattered and useless.

Anyway, my mother freaked out.

The good news is that I think my motor shafts are okay. My electronics also survived the accident.

I’m probably very lucky that I still have the skin on my fingers and got away with only a few cuts and a welt on my calf. Before I started this chassis build, I cut my thumb pretty badly when I lost my grip on a motor that suddenly accelerated to full speed and landed in my hand (it stopped when it spun itself free of the battery). The jagged edges of the broken rotors would have done much more damage. Why do I never learn from mistakes?

TODO: clean up mess, order new propellers, rebuild chassis, test, test, and TEST CODE.

Raiderbot X Meeting 7, 35 Days to Robot Ship

Meeting time: 15:00 to 19:00
Hours logged: 47.86

We attached our 2005 game arm to the kitbot. It works! It’s a pretty big arm even though it doesn’t quite reach 10 ft. I can’t wait to see our four-bar linkage arm finished.

Ordering parts… We need another cRIO, but I can’t find cRIO-FRC. NI has something that looks similar, but I’m not entirely sure it’s the right one.

ES and DP are building a battery cart. I’m surprised at how complex they are planning for it to be, at least in the electronics and software aspects. It sounds like a great project. That said, I will need to keep an eye on them to make sure they don’t go for too much. I think they can finish, though.

Raiderbot X Meeting 6, 36 Days to Robot Ship

Meeting time: 10:00 to 18:00
Hours logged: 44.05

Nothing markedly eventful happened today. Logging here for the sake of logging.

Spent forever soldering the wattmeter leads to Anderson plugs (iron isn’t powerful enough for 6 gauge wire), but the wattmeter works. Battery test bot pulls 30 A with wheels freespinning on toat, 120 A at stall. Circuit breakers are breaking!

Filled out purchase orders. Searched but could not find AS5040 encoder breakout boards anywhere other than on their official website. We need to order photoswitches as well.

Subdomain randomagically works! I needed to change “NameVirtualHosts cvhsrobotics.net” back to “NameVirtualHosts *”. Emailed Mr. R and got sandbox subdomain registered.

Talked with Will about goals for next Wednesday.

Raiderbot X Meeting 5, 38 Days to Robot Ship

Meeting time: 10:00 to 18:00
Hours logged: 36.74

Programming

The idea this year is to overload the bots with sensors of all kinds. Current sensors on every wheel, arm joint, and main circuit breaker to graph power consumption. Proximity sensors to avoid collision with other bots and facilitate scoring (automate entire process!). Encoders, gyro, and accelerometer for inertial measurement. And of course, line trackers for line following. I foresee lots of debugging, though it should help that the programmers have switched to Java+Netbeans that allows for serial communication with the cRIO.

Team 955 will now be using Git for version control. Git repository created here on Github.

Rockwell Automation Photoswitches

There is a wiring diagram on the back of the sensor box. L.O. and D.O. are light output and dark output, respectively. Power supply should be between 10.8 V and 30 V. See this Chief Delphi thread for more information. In the end, hooking it up to the cRIO is as simple as soldering brown to positive, blue to ground, and either white or black to signal of a PWM cable (which is true when either is light/dark?) and connecting the combination to Digital I/O. It is NOT necessary to hook up bleeder resistors from the signal lines to VCC as it says in the datasheet.

The datasheet is very useful:

  • Green LED on: sensor powered.
  • Green LED off: sensor not powered, output active, SCP* active.
  • Yellow LED on: output on.
  • Yellow LED off: output off.
  • Yellow LED flashing: output SCP active
  • Orange LED on: margin** > 2.5.
  • Orange LED off: margin < 2.5

* Short-Circuit Protection
** The orange LED shows that the signal strength is at least 2.5 times that needed to trigger an output. Signal strength is greater with higher voltages (obviously). This can be useful to overcome dust on the lens. The sensor’s sensitivity can be adjusted also by turning the knob on the front panel of the sensor. With an oscilloscope, I found that at maximum sensitivity, the photoswitch is triggered by almost anything (e.g., the table, paper, my red 955 sweater, my jeans) even at 10.8 V. We will need to test and calibrate the photoswitches so they trigger only over the reflective tape.

The datasheet recommends that the distance from the sensor to target to be at least 6 mm.

Standardized ordering process

Blanket POs from Will and Mr. A. Co-PMs and division leaders are the only ones authorized to order. Use order form on team website.

Minibot

TETRIX parts list:
2 – Motor Mount, W739089
1 – Motor Shaft Hub, W739079
2 – DC Motor, W739083
1 – Gear Hub Spacers, W739090
1 – Tetrix Resource Kit*, W731900
1 – Battery Charger, W739059
1 – 12V NiMH Rechargeable Battery, W739057
1 – Power Switch, W739129

* The Tetrix Resource Kit contains the parts shown here. Unfortunately, I haven’t found a detailed list containing only the Resource Kit parts, so we have to use the detailed parts list we found earlier here to identify the kit parts.

The default kit seems to have enough parts in it for one minibot. Once the minibot team has a reasonably complete idea of how they want to build their two minibots, they’ll let me know of any additional parts they’ll need. We’ll see exactly what parts we have when the kit arrives (hopefully) later this week.

Sent an email to PHRED about the possibility of exchanging FTC parts for FRC parts. They apparently no longer plan to build a minibot.