04062014 Spring Bot Update

Apr 07

We had a rather exciting end to our work session yesterday, but before we get to that… here’s a video from last week:

 

Now onto Sunday’s events… here are some of the other challenges we worked on.

Temperature sensor – work continued on a circuit to monitor the temperature of the motor.  The current implementation includes a Raspberry Pi, Arduino and a LM335 heat sensor.  Calibrating this setup has turned into more of a learning experience than anticipated.

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Vex and digital relays – the previous week  when working with the vex controllers to test the various lighting accents, we noticed that the digital relays tend to chatter – rather than clicking once as they changed state when the joystick button was pressed, they seem to click several times in rapid succession (sounds similar to when 2-3 year old discovers that he/she can make the lights blink on and off by flipping the switch very quickly – anyone else have that experience?).

Some investigation on the Vex forums confirmed what a couple of our mentors had suggested – that when trying to set up a “toggle switch” with the vex controller, “debounce” code needs to be implemented.  The forum explanation posted was that the microprocessor is extremely fast and the code may be able to detect several individual switch open/closes each time the button is pressed or released 1 time.  For any who are interested, 2 ways to get around this problem:

  1. Put a delay in the loop checking the status of the button so that it is checked every x milliseconds (anything over 100 milliseconds seemed to work here)
  2. Use variable to remember the state of the button from the previous time(s) through the loop.  For example don’t change the state until the code has been executed x times (50 was suggested).

(actual post can be found here:  http://www.vexforum.com/archive/index.php/t-9551.html)

We did some additional testing today with the program and are able to confirm that using a delay does eliminate the “chatter”.

Lights effects #3 (Light Bar) – we were able to install this in it’s final location, mounts had been welded to the frame the week before.  We have found a source for the correct adapters for the wiring to properly connect this device to the controller and power.  Hopefully, we’ll have them by our next work session and we can call this implementation done.

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Liquid cooling – The big effort yesterday had to do with installing liquid cooling for the motor.  The previous week we were pleased with the mobility of the robot in testing but did notice that it seemed to get very hot and that the self resetting relay was tripping more frequently than we’d like when contemplating a long walk in the parade.

A liquid cooling system was engineered out of copper tubing and a windshield wiper sub-assembly (tank and pump). The copper tubing was wound and placed around the motor housing, the tubing connected to the tank and the pump wired to the electrical system.   We turned it on and it worked the first time – the cooling system that is.

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We drove the robot down the driveway but didn’t get very far before the self setting relay tripped.  We wait a little bit for it to reset, drove another 12-15 feet and it triggered again.  It was definitely not running as well as the previous week (what a great drill for figuring out what to do if the robot breaks during the parade – what tools should we keep with us?).  We tried again, the relay would trigger… and then again… and so on until….  POOF! the motor controller (the device the Vex cortex connects directly to) lit up and destroyed itself (if you look closely you might see a hint of smoke).

destroyed controller

We suspected that the the self resetting relay would be melted and destroyed inside so we opened it today to see… but were not able to detect any visible damage.

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We’re not sure what the problem is just yet, but we hope to disassemble the motor for a closer review before our next work session this weekend.  Hopefully we’ll have some photos to post of what exactly is inside the motor.

 

 

One comment

  1. Beardedman /

    Sorry I missed all the fun, but happy the cooling idea “worked.” I’ll pull the motor apart and see if I can find out why the motor is pulling so many amps and creating so much heat.

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