Minibot Falling Solutions

[Christian Z]

well we were thinking of not using the brick but we didnt want the motors to be at full power so they don,t burn out.

[sam_who]

Doug G - Is that Bertrand Russell the amateur rocketeer?

[Kevin Sevcik]

So I've had a brainstorm that I'm both anxious and terrified to try out. Those Tetrix motors are expensive after all. All this requires is a standard 4-way light switch and a little faith. For those not in the know, a 4-way light switch takes two inputs and swaps them back and forth. Switch up and A->1, B->2, switch down and A->2, B->1. So, if you have an appropriate drive mechanism, one creatively wired 4-way switch should be all you need to reverse your robot and bring it down at a moderately controlled speed.... Now, stay with me here, cause this is a little crazy.

To get a 4-way switch to reverse your motors, you'd wire battery + and - to the input side, and motor + and - to the output side. Switch up, motor goes one way (up), switch down, motor goes the other (down). Wire both motors to the output, and they both get reversed. Rig this to reverse the motors at the top, and after your minibot's meteoric rise to the target will come a much much more meteoric plummet to the earth.

So how about this.... Wire one motor to the 4-way output normally. It gets reversed at the top. For the second motor, wire ONE lead to the correct (upwards) 4-way output. Wire the other motor lead straight to the correct battery lead. When the switch is flipped, this second motor is gets shorted to itself across the switch, causing it to regen brake, thus slowing down the minibot a rather good bit.... I think. But this circuit looks like it might have some... interesting... dynamics, as the second motor is in the return current path of the first motor, which I'm having trouble thinking out properly at the moment. So don't try this at home yet until I work out whether I'm being a little too clever here.

To the electricians in the audience, yes, you could hook the second motor up to its own 3-way switch to isolate it from the circuit, but that's a whole extra switch's worth of complication and weight. We're on a strict diet here, man!

[kromero18]

Originally Posted by nitneylion452

What if we buy a really long overcoat and have 3 people stand on each other's shoulders, then they wear the coat. It would appear that it is one person, but it's not.

love this idea! it should work

[2bkrul]

Originally Posted by jhellr13

Yeah, that rule is so hard to interpret. Hopefully it will be interpreted into greater depth in a future team update.

Why don't you have your mentor or another team member go on the Q&A and ask. Yes CD is helpful by getting others opinions on rules, but the GDC knows ALL.

Just sayin'

[mott]

As with other portions of Team Update #6, this Minibot retrieval rule leaves some room for interpretation.

What does everyone think of this: If you actually carried a "retrieval stick" or gaff-like device on your hostbot throughout the match (and subjected it to Robot Inspection with the rest of your machine), would this device actually qualify as "special equipment"??? Or, we could be creative and make a long section of our Bumpers have a hook (also known as attachment hardware) that we could hook our Minibot with to pull it down...

If your retrieval stick is part of your Hostbot/Robot (even though without function during the match) could it be considered "special"?

Comments welcome but a GDC Q&A might be in order.

[Karibou]

Originally Posted by Kevin Sevcik

Have you empirically tested this yet? I'm roughly estimating you'd need someone atleast 6'6" to make that reach. And that's assuming your minibot hangs down 12" from the target. You'd need someone about 7'2" to reach up to 122". This is assuming my rough body proportions math scales properly, and no jumping, of course.

If you have a girl (...or a guy, I suppose) that's 6', it's not incredibly hard to find 6" high-heels. Just throwing that out there.

Now that I think about it, would stilts be considered "special equipment" if they were worn by a drive team member during a match? They wouldn't have to be more than a few feet high. I wonder if they would be legal, as unlikely as it would be.

[Joe Ross]

Originally Posted by Karibou

If you have a girl (...or a guy, I suppose) that's 6', it's not incredibly hard to find 6" high-heels. Just throwing that out there.

Now that I think about it, would stilts be considered "special equipment" if they were worn by a drive team member during a match? They wouldn't have to be more than a few feet high. I wonder if they would be legal, as unlikely as it would be.

Your arm length is approximately the same as your height. Thus, if you're 6 inches shorter, your reach is approximately 12 inches less, so you'd need 12" platforms.

[Kevin Sevcik]

I was actually working this off general body proportions and some fudging for stretching up and standing on your toes. My mostly guesswork formula comes out as Reach = Height * 11 / 8. I'm 70" and I can reach my 96" ceiling standing on my toes, so all of my data points agree well with my formula....

[JB987]

There have been several demonstrations of great performing minibots slowly returning to the base of the tower after reaching the target. Kudos to them. Given Update #6 restriction on using assistive devices to retrieve a minibot is there a team who has figured out how to achieve a slow return willing to share their solution as a way to help possibly hundreds of teams avoid the potential damages likely to happen from free fall situations? For example, many teams designs won't be able to take advantage of a shorting of motor leads to act as a break of sorts because they don't backdrive. I don't see how sharing would give away any potential competitive advantage since it has no effect on the race to the target... and see great advantage to helping a fast minibot that could be potentially be your alliance partner stay intact enough to benefit your team as well...

[artdutra04]

Originally Posted by JB987

There have been several demonstrations of great performing minibots slowly returning to the base of the tower after reaching the target. Kudos to them. Given Update #6 restriction on using assistive devices to retrieve a minibot is there a team who has figured out how to achieve a slow return willing to share their solution as a way to help possibly hundreds of teams avoid the potential damages likely to happen from free fall situations? I don't see how sharing would give away any potential competitive advantage since it has no effect on the race to the target... and see great advantage to helping a fast minibot that could be your alliance partner stay intact enough to benefit your team as well...

When a DC motor backdrives, it acts like a generator and generates electricity. To slow the backdrive, add a load onto the system by isolating the motor from the battery and shorting the two motor leads together after the Minibot reaches the top of the pole. The Minibot will then roll down the pole slowly.

[JB987]

Originally Posted by artdutra04

When a DC motor backdrives, it acts like a generator and generates electricity. To slow the backdrive, add a load onto the system by isolating the motor from the battery and shorting the two motor leads together after the Minibot reaches the top of the pole. The Minibot will then roll down the pole slowly.

Thanks for sharing Arthur...as you were adding to the thread I was editing to mention that many teams won't be in a backdriving condition that could take advantage of shorting the motor leads...so what other alternatives are out there?

[artdutra04]

Originally Posted by JB987

Thanks for sharing Arthur...as you were adding to the thread I was editing to mention that many teams won't be in a backdriving condition that could take advantage of shorting the motor leads...so what other alternatives are out there?

You can use a DPDT switch to reverse the motor direction when it hits the trigger. To stop the robot at the bottom, a limit switch could be added.

[JB987]

Originally Posted by artdutra04

You can use a DPDT switch to reverse the motor direction when it hits the trigger. To stop the robot at the bottom, a limit switch could be added.

We have considered using a DPDT (4 way?) switch but were concerned about the downward velocity...the question is, could a limit switch (perhaps on a flexible extension) on the bottom end fit within the size limit and be far enough extended to provide a timely stop of the robot likely traveling faster than it did upward? An idea to be tested for sure. Thanks again, Arthur, for your efforts to help your fellow FRC mates!

[Ethan Spitz]

Originally Posted by artdutra04

You can use a DPDT switch to reverse the motor direction when it hits the trigger. To stop the robot at the bottom, a limit switch could be added.

Or for teams not using a NXT, you could use your second light switch to just completely cut the power. Of course in conjunction with the DPDT switch (or 4-way switch I believe it is also called)