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.

Tricopter: Prototype Chassis

I am sadly and pitifully deprived when it comes to building stuff at home. I didn’t even have a drill before I started this build.

Anyway, I didn’t have scrap plywood, but I did have scrap circuit board. I sandwiched wooden arms between two scrap PCBs and bolted them with 2-52 bolts (the only kind I have a meaningful quantity of) that are way too thin and will probably bend.

Again due to my dearth of tools, I cut the wooden beams using a drill (and broke the bit). I found a fold-out saw later that was much easier to work with.

I tested a rotor unit (motor + propeller) by mounting the motor on a long piece of kindling and clamping the kindling to the 1/2″ thick wooden cutting board that is my workbench. At about 70% throttle, the rotor nearly lifted the cutting board. I wouldn’t bring it to full throttle even behind a polycarb shield.

The tail motor mount was a bit tricky, but I managed it. I would take pictures if I had a camera.

I will mount the tail motor and hook a stiff wire (paper clip?) between the servo arm and the rotational unit once the epoxy cures.

Raiderbot X Meeting 4, 39 Days to Robot Ship

Meeting time: 15:00 to 21:00

We are two days behind schedule. I started a WOT (Weighted Objectives Table) discussion of the various lift concepts at 3:30. We started with seven concepts:

  • Single-jointed arm
  • Multi-jointed arm
  • Telescope (elevator)
  • Four-bar linkage
  • Eight-bar linkage
  • Scissor
  • 60/40 scissor

We narrowed it down to the four-bar linkage and the elevator and chose the four-bar linkage after a qualitative analysis using a pros/cons list for each. But I still wonder if this was necessary, because it took another 30 minutes of our time and I ran 45 minutes past my proposed deadline of 4:30. Why couldn’t we have reconsidered the two options using the three factors we had rated most highly? Will says some people just need more stake in things? Anyway, my bad for not calling them on it. Areas of improvement:

  • Do not let the loudest voices steer the discussion off-course.
  • Constantly think back to previous discussions and decisions. People were putting the WOT factors under the pros/cons lists, which is nonsense.
  • As always, be consistent, even when calling out for hands when rating the WOT factors. This is no time for jokes.

Will then separated us into four design groups for the lift, claw, base, and minibot.

Four-bar linkage: Mr. Groom found that making the shoulder pivot points’ distance shorter than that of the elbow pivot points allowed the claw to point down when the arm is down and point up when the arm is up. This should allow us to reach both the ground and the top peg as well as everything in between. This makes sense if we think about the four-bar linkage as a trapezoid and shifting the two bases—the linear displacement for the two lever arms is equal but the arm lengths are different, so angular displacements differ.

Minibot: make it as close as possible to a battery with motors glued on.

Preliminary design review planned for Saturday 17:00.