Minibot Falling Solutions
 

There might be multiple threads of this question, but i would like to make a general one with multiple ideas.

My team today has built a minibot prototype, and it works pretty good. We are running into a problem when the minibot slides down from the top. The minibot moves great upward, but drops like a stone.

What are some of your team's ideas on keeping the minibot's downward movement controlled and safe to avoid a hard crash?

Re: Minibot Falling Solutions
 

We were hoping that the motor, being geared, would provide enough resistance to falling. Our main concern, though, is getting the motors to stop because I was trying to see how much torque the motors provided by trying to stop the wheel from spinning. Good news: plenty of torque. Bad news: motor began to smoke after a few seconds.

Re: Minibot Falling Solutions
 

Try putting memory foam at the bottom of your bot. A nice soft landing.

Re: Minibot Falling Solutions
 

Start thinking some more, this is illegal per Team Update #6.

Re: Minibot Falling Solutions
 

Memory foam isn't on the approved materials list. Your only potential options would be rubber bands, surgical tubing, non-slip pad, or hook and loop fastener.

Re: Minibot Falling Solutions
 

Yeah, we have a 1 to 2 gear ratio, and it just falls ways too fast.
Our motor as well has begun to smoke


Memory foam sounds like a great idea, but does it effect the weight strongly?

Re: Minibot Falling Solutions
 

Double posting so I don't have to edit a post...

Are these minibots falling/dropping just from the weight of the minibot backdriving the motors? I'll admit I haven't looked to see how fast they backdrive, but falling like a stone doesn't seem likely... If this is the case, however, I vote rigging up a light switch to switch the positive lead on one or both motors from the positive battery lead to the motor's negative lead. Instant regen braking and all that.

Re: Minibot Falling Solutions
 

We are planning on using a switch to start the climb, and a switch to make the minibot stop at the top, and then move down slowly. I'm sorry "dropping like a stone" is somewhat an exaggeration, but it just doesn't slide down at a slow, safe pace.
What do you think now that memory foam is not allowed?

Re: Minibot Falling Solutions
 

Memory foam was never on the allowed materials list for the Minibot. However, it's not on the disallowed materials list for the Hostbot.

I had an idea: If the robot's arm just so happened to be up at the end of the match, just so happened to be about 10' tall, and just so happened to have a device at a shoulder joint that would allow any claws to be operated by hand without robot power being turned on, I don't think the refs can use the "special equipment" rule to disallow that being used to bring the Minibot down. It's part of the Robot, after all...

Re: Minibot Falling Solutions
 

http://www.chiefdelphi.com/forums/sh...inibot+warning

It explains a solution for prototyping, but not for the real bot. Surgical tubing or something on the bottom might help.

Re: Minibot Falling Solutions
 

I know it was never allowed. And your idea sounds very possible and smart. Our team is deploying our minibot by using drawer glides attached to a scissor type of device. I thought with your idea, if it would a good idea to put the memory foam on the end of the scissor where the minibot would deploy onto the pole. Now my concern is the hostbot is allowed to have a part of itself on the pole platforms when the minibot is deployed onto the pole

Re: Minibot Falling Solutions
 

c/p from team update #6

<G59> TEAMS must retrieve MINIBOTS from the TOWER quickly and safely without special equipment and while standing on the floor after each MATCH. Violation: The FIELD crew will retrieve the MINIBOT if the TEAM does not. A second violation may result in a YELLOW CARD.

so you kind of need the minibot to come back down now or you need some really tall team members.

Re: Minibot Falling Solutions
 

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.

Re: Minibot Falling Solutions
 

Yes, but does the hostbot need to be completely off the pole tower before deploying the minibot?

Re: Minibot Falling Solutions
 

Wrap the coat in tin foil to give that metallic look too

Re: Minibot Falling Solutions
 

<G43> allows the HOSTBOT to grab the TOWER during DEPLOYMENT.

Re: Minibot Falling Solutions
 

Does this apply?Doesn't say how long the restriction lasts after the MINIBOT has crossed the DEPLOYMENT LINE.

Re: Minibot Falling Solutions
 

Considering the penalty is just a disabled tower, and the fact that the towers are disabled after the match...

Regardless, if the GDC were to outlaw the HOSTBOT from having an attached extension to retrieve the minibot, it would seem rather silly.

Re: Minibot Falling Solutions
 

Thanks for the reply. Idk if you read the previous posts, but our team is using a deployment system containing drawer glides and a scissor to guide the minibot to the pole/tower. Someone before said that putting memory foam on the hostbot is not prohibited. If my team were to put memory foam on the end of the deployment system such that when the minibot falls(let's hope not), it will hit the memory foam, would this be allowed?

Re: Minibot Falling Solutions
 

If the MINIBOT is allowed to contact the HOSTBOT again after the TOWER is TRIGGERED, then using the memory foam as a soft landing pad would be a valid idea. But I don't know how <G22> is going to be interpreted.

Re: Minibot Falling Solutions
 

lucky for us we have ryan, who is that tall.

Re: Minibot Falling Solutions
 

You could always build a bunch of mini-bots then let the field crew rip it down every match. (The sad part is I'm only half joking:rolleyes: ) Has the actual way they plan on getting a stuck mini-bot down been revealed? I'm guessing miniture chainsaw mounted on pole.

Re: Minibot Falling Solutions
 

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.

Re: Minibot Falling Solutions
 

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

Re: Minibot Falling Solutions
 

By shunting your motors when they get to the top, it will allow them to return back down at a slow and constant velocity. Ever drop magnets down a copper pipe? The same principle works for the motors. If the motor wires are shunted together, back emf will in effect prevent the motors from backdriving to fast. The trick we're still figuring out is how to switch the battery power off FIRST then shunt the motors SECOND. It's all about careful alignment of switches. Of course there's always the fuse that blows if it happens in the reverse order.

Re: Minibot Falling Solutions
 

Yeah your thoughts are true. Today was our first time running the minibot on the pole. We are still developing it though. We also were running it on the standard robot battery, rather than the small battery meant to be used on the minibot. We still have to cut some weight and program the minibot, so things might change.

Re: Minibot Falling Solutions
 

well if you our using an NXT brick and a motor control you could simply change the speed of your robot to a low power so the minibot will stop where you want it to.

Re: Minibot Falling Solutions
 

Our team has decided not to use the NXT brick partly because it is added weight and because it isn't really needed. Our plan is to use a switch to activate the minibot when it hits the pole, and a switch to turn it off at the top, in hopes that it will slide down at a nice pace due to friction.

Re: Minibot Falling Solutions
 

What do people think about backdriving the motors down the pole?

Re: Minibot Falling Solutions
 

We tried to reverse power ... doesn't work for our design.

What does work for us, assuming the bot stays up .... is to shake the pole just a little and the thing comes down either backdriving or falling.

Either way, its a good thing if we can catch it.

Re: Minibot Falling Solutions
 

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.

Re: Minibot Falling Solutions
 

Doug G - Is that Bertrand Russell the amateur rocketeer?

Re: Minibot Falling Solutions
 

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!

Re: Minibot Falling Solutions
 

love this idea! it should work :P

Re: Minibot Falling Solutions
 

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' :]

Re: Minibot Falling Solutions
 

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.

Re: Minibot Falling Solutions
 

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.

Re: Minibot Falling Solutions
 

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.

Re: Minibot Falling Solutions
 

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....

Re: Minibot Falling Solutions
 

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...

Re: Minibot Falling Solutions
 

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.

Re: Minibot Falling Solutions
 

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?

Re: Minibot Falling Solutions
 

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.

Re: Minibot Falling Solutions
 

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!

Re: Minibot Falling Solutions
 

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)

Re: Minibot Falling Solutions
 

If you are using two motors, what if you use a two DPDT switches: one reverses one motor to drive it downwards, and the other switch shorts the leads of the second motor to provide drag. We 're probably going to experiment with either partial reverse/motor short or full motor short this week on our Minibot prototype.

Re: Minibot Falling Solutions
 

Let us know how things work out...we will be trying several methods and will share our trial results also. In the meantime, it would be nice if others would do the same thing;)

Re: Minibot Falling Solutions
 

I am 78" tall, but with no shoes I can only reach around 102" while standing on my toes. While the tall person idea is viable, I would want to test it before it was my job to pull down the minibot. Also take into account that you are not right under the minibot, but 12" away from the pole.

Re: Minibot Falling Solutions
 

Don't mean to self-quote here, but I had a thought earlier today and put it in the wrong thread.

...

Re: Minibot Falling Solutions
 

well if you cannot get the minibot to slide down slower, than i would suggest putting some kind of cushioning at the bottom of your bot. As for slowing down the fall, maybe tightening the minibot's grip on the pole enough to create more friction but still being able to move up smoothly or some kind of braking mechanism. Hope this helps guys!

Re: Minibot Falling Solutions
 

We are using 2 three-way switches (SPDT) to create an H motor control. We are also using 2 TETRIX on/off switches to start/stop the motors. On our MINIBOT the motors need to turn in the opposite direction but the H motor control reverses both motors. Finally, we are planning on using stainless steel axles to flip the switches and surgical tube to absorb the shock of contact. We are using a latch so the axle does not bounce back and flip the switch again.

Re: Minibot Falling Solutions
 

G59> TEAMS must retrieve MINIBOTS from the TOWER quickly and safely without special equipment and while standing on the floor after each MATCH. Violation: The FIELD crew will retrieve the MINIBO

what is special equpiment? If you made a second minbibot that you would release after the match to retrieve the mini bot at the top. no need to use a long pole if you have a robot to get a robot.

Re: Minibot Falling Solutions
 

What is acceptable for a MINIBOT limit switch?

Do you think a DPST plunger type push button switch like:
Digikey Part Number: 679-1048-ND
would be legal?

Would it be legal to activate the MINIBOT with this switch as it is deployed onto the pole?

Re: Minibot Falling Solutions
 

That is a panel mount switch. Doesn't look like, nor is it marketed as a limit switch. Also note the current rating is at '125 v A/C'

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The current Rating is 6 AMPs for this pb switch but I assume that is somewhat comparable to a household light switch. The rules specify max a 20 amp fuse so I would think that would be sufficient for current limiting.

Is there anyway I can get a First judge to respond to this?

Also, Is there a detailed list of the Tetrix components on-line? I have failed to find it and I wonder if there is a switch from that list we could use instead.

Re: Minibot Falling Solutions
 

As with anything else, the only way to get an official opinion is to use the Q&A on the FIRST website. You have to log in with your team ID found in TIMS.

Re: Minibot Falling Solutions
 

If you are running 2 motors. It is possible to run them at 1/2 voltage (potentially 1/2 speed) by switching them into series connection instead of parallel connection. This cuts the current thru the motors in 1/2.