How to get the mini bot down
 

It seems like every time I meet with someone or talk with someone about the mini bot they have 3 stock questions/comments.

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

2.How do we deploy it?

and this threads topic

3.How do we get it down?

I've been wondering this and the way we designed our mini bot, and the common theme I see with many, it would not be good to just reverse the motors, seeing it would just shoot down at over 32.2ft/s^2. While pondering this I was thinking

-Well why don't I just climb the pole and get it, well cause a few hundred people would yell at me for not being safe and wouldn't let me do it again.

-How about shaking the pole, same reason as not reversing the motors except this time it won't have such a predictable landing spot.

-Next was the giant pool skimmer idea, why not get a long pole with a net on the end, cause there's got to be a better way (although still plausible)

My final thought and question to you now is, why not just tip the tower over. Looking at the design of the tower it is connected to the field with just velcro, so are we allowed to just tip the pole over?

Re: How to get the mini bot down
 

You don't just tip something that's attached to carpet with industrial strength velcro. Trust me on this--I've done a little too much field setup/teardown. If you're lucky it's not on a base plate that is covered with carpet too--and that's just the setup I'd suspect.

Besides risks of damage and all that.

What if the motors could simply be stopped and allowed to be backdriven? Maybe with a slight loosening of pole clamps. This would allow gravity to take over, but in a (mostly) controlled manner.

How about a long pole with a fork on the end that fits around the pole? Put it above the minibot and pull down until it's within range of your tallest drive team member.

Re: How to get the mini bot down
 

that would make way to much sense though and it eliminates the fun of trying to get a robot off a 10 ft pole

Re: How to get the mini bot down
 

Eric,
Doesn't look like T25 allows us to bring "special equipment" to retrieve our minibots from the pole:
<T25> The only equipment that may be brought on to the ARENA is the OPERATOR CONSOLE,
reasonable decorative items, and special clothing and/or equipment required due to a
disability. Other items, particularly those intended to provide a competitive advantage for
the TEAM, are prohibited.
Granted, I don't see what competitive advantage a pole to retrieve a robot provides:confused:

Re: How to get the mini bot down
 

Bring a flag, use the flag pole ;)

Re: How to get the mini bot down
 

There is a way to get around it: make the device part of the robot or the operator console. (Obviously the robot isn't "equipment", because if it were, you couldn't bring it on the field; the console is equipment, but exempt.)

The part can be detachable, if you like. What's more, you arguably don't even have to have it attached to the rest of the robot during the match—its a modular component that you chose not to install during gameplay. (Just make sure to get it inspected as necessary; it would count toward weight.)

(Making it part of the robot is a standard solution to having an alignment device. In that case, it's a bit of a grey area whether those can be non-installed parts of the robot at the time of use. In this case, given the relative lack of ways to penalize you for it—because use occurs after the match—it's pretty much moot. Note that "moot" is distinct from "strictly legal"....)

An alternative is to ask the Q&A; they'll probably end up amending the rules to allow unpowered retrieval devices anyway.

Re: How to get the mini bot down
 

Our team and many others last year used special "tools" to get our robots down once they hung. We had two fairly large "U" shaped hooks that we would slide into our hooks to release our robot. This was never questioned by anyone, and we actually receieved many compliments for thinking ahead and creating the tools.

Obviously the standard disclaimer of "last year's rules don't apply to this year" also fits here, but that is just an anecdote of a similar situation from previous games.


Personally, I think having a team bring some kind of device to get it down that the mini bot and device are both designed to do together is a lot easier to deal with than having to rip down minibots with whatever device FIRST is going to use. Even with an extremely well designed minibot and retrieval method, things can go wrong that may cause your minibot to be stuck.

Sounds to me like the GDC should be asked about this to get some clarification.

-Brando

Re: How to get the mini bot down
 

The GDC already ruled that a small step ladder violated <T25> http://forums.usfirst.org/showthread.php?t=16331
It keeps your minibot from being destroyed by Dean's chainsaw, which is a big competitive advantage in future matches.

Re: How to get the mini bot down
 

Technically, by that wording of <T25>, tools to discharge a pneumatic mechanism and/or pick up a robot are illegal as well; yet I haven't seen a single judge or referee ever say anything about them. Particularly, Curved T-handle hooks are used by a few teams to pick the robot up. Usually these items are in the best interest of safety, and the only 'competitive' advantage they provide are allowing the drivers to safely retrieve game pieces and/or lift the robot without straining their back, in order to stay healthy for future matches.

It will be interesting to see the implications of enforcing <T25> as worded.

Re: How to get the mini bot down
 

The real alternative is to design your minibot to come down autonomously as it's last action so that it is at the bottom when you go to retrieve it...

Re: How to get the mini bot down
 

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...

Re: How to get the mini bot down
 

Our Victors have brake and coast modes. No reason you can't make a minibot have a "brake" mode too!

Re: How to get the mini bot down
 

Indeed...

Re: How to get the mini bot down
 

<R11>, blue box:
Now it doesn't say, one way or another, whether those are removable lifting bars or handles. But as has been noted, separate carrying devices have been used in the past.

... says nothing about after the match.

I'm not sure how this works with <T25> - someone will have to ask.

Re: How to get the mini bot down
 

I asked the question in Q and A today.

1. Is a pole legal to bring on the field to help retrieve the minibot.

2. If the pole is part of the robot and detached at the end of the match can it be used to retrieve the minibot?

3. If the pole is part of the drive console and is detached at the end of the match can it be used to retrieve the minibot.

I also mentioned that this is a safety issue and that this device would not give a competitive edge to any team.

It will be interesting to see what they say.
I personally don't know how they can no to either 2 or 3 and then it will be pretty silly to say no to 1...

We will see

B

Re: How to get the mini bot down
 

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

Re: How to get the mini bot down
 

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

Re: How to get the mini bot down
 

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



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?

Re: How to get the mini bot down
 

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.

Re: How to get the mini bot down
 

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? :)

Re: How to get the mini bot down
 

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.

Re: How to get the mini bot down
 

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

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

Re: How to get the mini bot down
 

<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:

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.

Re: How to get the mini bot down
 

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

Re: How to get the mini bot down
 

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

Re: How to get the mini bot down
 

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.