How to get the mini bot down

[JB987]

Thanks, Bob! I look forward to seeing a common sense reply from the GDC soon...

[dtengineering]

Originally Posted by jamie_1930

1. Everyone on CD says they can do it in 1.5 seconds, how are we supposed to compete with that?

Easy. SAY you can do it in 1.4 seconds.

If there is one thing I have learned in my seven years of FRC, is that what works with one robot on the practice field rarely works as smoothly when you have six robots crammed on to a playing field.

As for getting it back down, the easiest would seem to be to either have the motors turn off (a switch or a fuse, perhaps) and then let it backdrive down.

Jason

[davidthefat]

Have the minibot have an ejection system with a parachute. Its safe and its cool to have the bot just float down by itself.

Originally Posted by JB987

But the challenge is how do you get it to come down at a reasonable speed if you are not using the NXT to reverse and lower the motor speed used to climb the tower because you are using the lightest, bare bones design for the climb and if you are geared such that you aren't going to backdrive with gravity's help? Assuming you have found that such ratios that allow backdrive increase likelihoold of stall conditions for the climb...

Now I am not an EE major or anything; but can't you use resistors to restrict the flow of electrons to the robot? So less electrons flow through, the slower it goes. Isn't that how it works?

[JB987]

Resistors would indeed reduce the flow of electrons...trouble is I don't see resistors listed in R92 that details what can be a part of the minibot.

[WizenedEE]

What about a diode that would connect the two poles of the motor together when it's moving backward and not do anything when it's forward?

Like.. put the anode on the end where the 12V is applied and the cathode on the end where the GND is. That would reverse the diode when power was applied, but when the power was shut off and the motor started generating power, it would go through the diode and act as a brake.

Now if we build our own diodes out of some sort of electromagnet, is it legal?

[Jared Russell]

Even without a resistor, you can just shunt the + and - leads of the motors together to use the internal resistance of the motor itself as your brake.

Try spinning the shaft of a CIM with the leads disconnected from everything. Then connect the two leads together, and try again.

[Bill_B]

Originally Posted by dtengineering

Easy. SAY you can do it in 1.4 seconds.

If there is one thing I have learned in my seven years of FRC, is that what works with one robot on the practice field rarely works as smoothly when you have six robots crammed on to a playing field.

As for getting it back down, the easiest would seem to be to either have the motors turn off (a switch or a fuse, perhaps) and then let it backdrive down.

Jason

Words = easy - - - hardware = HARD - - - software = ????

If you're using a "fuse-switch" at the top, descent by backdrive shunt will be tricky.

[FRC4ME]

<R92> allows for the use of up to two "common household light switches."

So get a three-way light switch (which I believe still qualifies as "common"), which is basically a single pole double throw switch. Then wire it like this:

     -----
    |     |
    |     |
+ -----   |      switch
-  ---    |    ===========
    |     |   =           =    motor
    |      ---=--o        =   =======
    |         =        o--=---= +   =
    |---------=--o        =   =     =
    |         =           =   =     =
    |          ===========    =     =
     -------------------------= -   =
                              =======

And rig something up to flip the switch to the top position on deployment and flip the switch to the bottom position when the minibot reaches the target.

Of course, you might say that's easier said than done, but if you weren't going to use the NXT brick, you must have had something that could turn the motors on at deployment and turn the motors off when reaching the target? So use the same thing, but with a three-way switch so you get braking on the way down.

[EricH]

For emergency use, it is recommended that you put something that the Retrieval Hook can grab onto the Minbot. TU#7 addresses this; a design for said hook is out.

http://usfirst.org/uploadedFiles/Rob..._Update_07.pdf

[whosdadog]

For those unaware of the official retrieval hook. (Mentioned in the above PDF)

[Mr V]

Originally Posted by FRC4ME

<R92> allows for the use of up to two "common household light switches."

So get a three-way light switch (which I believe still qualifies as "common"), which is basically a single pole double throw switch. Then wire it like this:

A 3-way switch would certainly be considered common since in update #7 they state that a 4 way switch could be used to reverse the motors to make the mini bot power itself down the pole, which is something many teams have already figured out and posted in a couple of threads here. Plus the updated definition (don't remember which one) says that any switch found in your local hardware store designed to be mounted in a box is acceptable.