View Full Version : Controlling the Mini-bot. How?
01-09-2011, 07:11 AM
There seems to be a minor flaw in the allowed parts for the Mini-Bot.
I coach two FTC teams so I know the TETRIX and NXT systems pretty well.
Although the Minibot can have a battery, NXT, DC motor controller and Motors, there doesn't seem to be any good way to provide inputs into the NXT, and as any good roboticist knows, a robout without inputs is just a dumb mechanism.
The only allowed inputs seem to be "limit switches" and "Household light switches". Neither of which can normally be interfaced to the NXT. So if they are the only inputs able to be used to intelligently start and stop the robot (by interrupting the motor supplies) why have an NXT and motor controller at all?
I guess the thing that seems to be missing from the allowable materials are LEGO Sensors and associated cables, or the Hitechnic prototyping board, which would allow the NXT to read the switches.
I have purposfully ignored the buttons on the front of the next as inputs because they really aren't designed to accept much more than human fingers pushing them.
01-09-2011, 07:16 AM
The limit switches can be the touch switches FTC teams are familiar with. There is no rule that says the Minibot needs to be controlled by an NXT module only that you may use one and only one.
<R92> The following items are the only permitted materials for use on the MINIBOTS:
E. No more than one NXT controller with the Bluetooth functionality disabled,
01-09-2011, 07:34 AM
Oh, I agree that an NXT is not required, I was just thinking that the NXT and motor controller are a lot of weight to add to the mini bot if you can't get some inputs into it. It might just be usefull to do some "smart Motor control" prevent breakage and to help you return the bot to the ground at the end of play.
I'm not sure I'd be willing to assume that an inspector would equate a Limit Switch with a Lego Touch sensor (especially if they are an EE).
I guess I'll just have to wait for an official ruling.
01-09-2011, 07:42 AM
The touch sensor is an acceptable method of stopping the minibot through the NXT controller, is it not? The same as if a micro switch were used as a limit switch to halt travel.
01-09-2011, 10:10 AM
That's my point.....
The way I read the allowable parts... a Touch Sensor is NOT a legitimate method to stop the minibot's motion because it's strictly not a "Limit Switch" in the sense of the word (Just like an electromagenet is not a Solenoid actuator).
Yes, it's a touch sensor (I suspect that the phrase "limit switch" does not appear on the LEGO site anywhere.) that could be used to detect the end of travel, and be used to stop the bot. But so could a light sensor, or an Ultrasonic sensor (we do it all the time in FTC). Are these "Limit Switches" ? I think so, but would an inspector? What about an altimeter :)))
Without being more specific there is a world of possible interpretations of what a "Limit Switch" is. As usual if they are going to inspect these bots, the inspectors need a clear picture of what a Limit Switch is and is not .
If they really are merging the worlds of FRC, FTC and FLL, then "Any LEGO Part" starts entering the vocabulary.
01-09-2011, 01:02 PM
I was going to cross-reference this to the rules prior to posting, to see if "limit switch" had been given a specific definition in the rules (I don't remember seeing it yesterday when I read through them) but the FIRST site is responding slowly.
In the generic definition of "limit switch", the term limit describes a function, rather than a form. In other words, any switch could be a limit switch, so long as it's function is to limit the action or range of motion of a system.
Unless there is further guidance from Q&A, or something that I missed in the rules, I would think that you could use just about any type of switch to stop your motors once they hit the top of the pole, as that would be a "limiting" function.
I don't recall, however, seeing anything saying that minibot motors have to be stopped at the beginning or end of the match... so you could also build a mechanical system to release your climbing system from the pole once you have hit the top, and the motors could keep turning until you recover the mini-bot and unplug the battery.
I think it would be really interesting, however, to see a minibot built without batteries or a motor... not quite sure how I'd store the energy for the climb just yet, but there are plenty of "generic" materials choices available that might make it possible. If only "mousetraps" were on the approved materials list!
01-10-2011, 07:16 AM
The inspection team will take their direction from the GDC. If the GDC defines "limit switch" as anything that will limit or stop motion then we will use that definition. If they define it as a specific type of switch then we will use that definition. If you have a specific switch in mind, please ask the Q&A.
01-12-2011, 09:15 PM
The minibot will need to push hard enough to register a win. Unless you want to climb the pole for naught.
We have 3 FRC teams listed in the Rochester NY area. And many more FTC teams. I have no FTC experience, and am using the off time to try and teach our 12 student team ahead of the game. Having to build two robots in six weeks is almost twice as hard as having to build one. Especially when we haven't a clue what an FTC robot is. In short we probably won't play that part of the game as we usually run out of time.
01-12-2011, 09:17 PM
Luke us the autonomous.::safety::
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