Big Minibots
 

Since teams have been posting pics and vids of their robots and minibots something I have been noticing as been getting to me. Why is it that alot of teams are building these huge and complex minibots? I mean teams are building minibots that look like they are maxing out the size limits near 12"x12"x12". Why build a big one over a small one? Pros? Cons?

Re: Big Minibots
 

IDK - Because they can?

Re: Big Minibots
 

Why bother to even start this conversation?

It's pretty apparent from your remarks that you already understand that others' design processes greatly differ from your team's design process.

Re: Big Minibots
 

Such negative posts. The reason I started the thread was to see if anyone with a huge minibot would post as to why they made theirs so big compared to a really small one

Re: Big Minibots
 

Jack and Jesse,

There are many advantages to having this kind of thread.

The original poster was asking why the decision was made for the large minibot. Do they feel that the additional weight is counteracted by something? If so what is it?

Please don't post in a thred to belittle the person asking a legitimate question.

Re: Big Minibots
 

In fairness to Jack and Jesse, the original post was worded in a way that seemed to insinuate that a larger minibot is a terrible idea that no team should have used. As a mentor of a team that has built a larger minibot, I will say that it mostly came down to us finding a design that worked for us. Could our design be more compact? Probably, but after several design iterations that failed miserably, we are happy to have a functioning minibot regardless of its size.

Re: Big Minibots
 

A 4 inch minibot has more distance to travel to the top than a 12 inch minbot. Ours is at the max of 12 inches and can travel up much faster than some a fraction of its size and that is before lightening and speed holing!

But we are definitely not faster than 118,148,217,and 1114! ;)

Re: Big Minibots
 

That all depends on how close to the deployment line you deploy either of them.

Re: Big Minibots
 

That is true, but again it depends on where they deploy from and I have seen several deploying near the bottom.

Re: Big Minibots
 

We didn't figure out how to make a small minibot.

I expect many other teams have the same reason.

Re: Big Minibots
 

Just put it in the dryer for a few extra cycles. That should shrink it down nice and small.

Re: Big Minibots
 

Our team just sort of figured that it would be easier to try to push 5/6 pounds up the pole, instead of 12-15 pounds. We want to maximize the traction, using 2 wheels, and minimize the drag. We aren't using magnets to hold ourselves, close to the pole, because of drag. We using 2 semicircular pieces of PVC, that are connected, like a hinge and open, before deployment, and snap together, after deployment. The magnets will hold the open ends together.

Re: Big Minibots
 

I think that this trend partly results from using the Tetrix structural components in one's minibot. When my team was prototyping designs using Tetrix parts, we found that we had to have significant structural members to get things like motors, gears, and wheels in proper stable alignment. When we later built a custom minibot body, we were able to mount all the components exactly where they needed to be, saving weight and volume.

Then again, we ARE using a minibot that has a single motor and wheel...

Re: Big Minibots
 

our 15 lb minibot gives our hostbot the extra traction it needs to push around other robots with ease. :)

edit - We didn't actually do this, but I wanted to... I am sure some teams did it.

Re: Big Minibots
 

The most obvious thing I can think of is that a taller minibot can be deployed closer to the ground and hit the target as soon as a shorter minibot. Depends on the design.

Re: Big Minibots
 

Potential reasons:

1. Because they don't have someone who understands Physics leading the design.
2. Because they don't read Chief Delphi
3. Because they are ignorant of the world around them.
4. Because they lack the resources, or design experience to build something custom

I don't mean this post to be harsh. I lot of teams have put a lot of work into some very successful larger minibots. But as a matter of engineering and physics principals, a small and light one is the only correct way to do it, if the goal is to get to the top the fastest.

Re: Big Minibots
 

As a famous engineer likes to say, design is an iterative process. I've visited the pits of a few teams* that began by building larger, heavier minibots, and evolved their designs toward smaller, lighter minibots. The physics is the same, but the numbers (weight, friction, wheel diameter, gear ratio) are different. Lighter = faster, after you get the design optimized.

*One of those teams has a leader who is also a physicist, and a teacher. I am certain she did not do the design for them, but I am also certain she did not allow them to believe their first design was good enough. The advantage of understanding the physics behind an engineering problem lies in knowing how to predict the theoretical best-case result -- after you have that knowledge, iterate until your actual result is so close that further effort is better spent on something else.

Re: Big Minibots
 

Consider two teams on a dysfunctional alliance: both race to the same pole at the same time from opposite directions...

One has a 15 lb maxi-minibot...
the other one has a 2 lb mini-minibot...

oooh, the horrible noise.., then...

the maxi-minibot slowly climbs the pole with what's left of the mini-minibot wrapped around the maxi-minibot's chrome hood ornament. ;)

Aaahh, but it's the twisted wreckage of mini-minibot that flattens into the tower plate with no worries about not providing enough force for long enough.

But no points are awarded because the mini-minibot did not use power from its battery and motors to climb the pole.


----


Can a 15 pounder with a "cow catcher" intentionally scrap off little minibots that get stuck on the pole?

That might be fun to watch.


----
We design for being on a dysfunctional alliance: all the time.

Re: Big Minibots
 

I think it just ends up what works for you and your materials. If you can only use the Textrix parts and you don't have access to custom parts, you probably will have a bigger and heavier minibot. Its not that you are ignorant or anything its just what works for you and what you have. If you have unlimited resources you probably will have a small light minibot.

Re: Big Minibots
 

If one of the resources is "engineering talent", then yeah, having more resources helps. But you don't need much as far as tools/equipment/money to build a nice one. 330s minibot is amazing.

Re: Big Minibots
 

I normally respect your opinion but let's look at engineering and physics for a minute...

How many of those "small and light" minibots are using limit switches rated for AC only? Answer: All of them.

From an engineering perspective, this is reckless and stupid. AC current switches through zero 120 times a second and the arc created when one tries to open a circuit is extinguished.

This does not happen for a DC current. It is much harder to switch... The arc tries to bridge the gap resulting in contact pitting and/or welding. This arcing becomes even larger when switching inductive loads (like DC motors).

To pick an example, the Honeywell microswitch in the KOP is rated for 11 amps AC only. An electrical engineer would never use it for DC currents except at milliamp (logic signal) levels. And in the extreme cases where expected lifetime is measured in thousands of cycles, never at all...

Now, you can specify DC rated microswitches but they ain't so micro...

So... We have teams who use NXT controllers and NXT touch sensors and they end up with large, non-competitive but better engineered minibots. And then we have poorly engineered but competitive minibots whose mentors have turned a blind eye to good engineering and are just hoping that they get though the season without failures setting in.

The correct way is not necessarily the competitive way...

Just who is ignorant of physics or of the world around them?

Regards,

Mike

Re: Big Minibots
 

All valid points. Perhaps I should have been more specific in specifying engineering for the task at hand which is getting up the pole in the least time, with a life cycle of only a few times.

I completely agree on the switches. It's bad practice to use a switch for something it isn't meant for. In this case, it does seem to work, for a little while anyhow.

Re: Big Minibots
 

Wow,
I didn't realize that you could be wrong three times with three bullets. I don't mean this to be harsh, but here is where you are wrong.

1. my kids understand physics. Since that's what I teach, I make it my mission to sneak it in when I can.

2. I read CD as well as a few other members of the team. I'm not quite sure what was meant by this statement. We should all take the best ideas and use them as our own? Wouldn't that make this whole process so VERY boring? Yeah, I pointed out the "one day minibot" to my team today. They thought it was very cool but is beyond our ability to make (the most complex machining tool we have is a drill press). They want to focus on a consistent deployment system after watching 3 weeks of events. To sum up the mood of the team: getting a 4 sec minibot up the poll every match >> 2 sec minibot up the poll 80% of the time.

3. ignorant is such a "large" word to use. I'm not sure how to respond to that, so I won't.

Some teams want the students to learn something along the way (i'm not saying you don't Sand). FIRST gave them the problem. They are the ones who are deciding how they chose to solve the problem. I can point out the mistakes and help them along the way, but I refuse to do it for them.

I think it comes down to how you want to inspire your team. I have my way, other mentors have different ones. Who knows which is best. I don't. I don't think anyone truly can. What I can say is there isn't one correct way to do anything.

Re: Big Minibots
 

Because ours worked 100% of the time.

Re: Big Minibots
 

This is FIRST. People shouldn't give a hoot about lifetime ratings in this case; the part needs to last a grand total of about 1-2 minutes max in competition. I'd take something even lighter than the KoP Honeywell switches if I could get my hands on them. It is better engineering to realize that the task at hand requires performance wayyyyyy over survivability.

Re: Big Minibots
 

i'll remember to tell that to a team who's minibot burns out half way up the poll in elims.

Re: Big Minibots
 

1) although it may be common for teams to use AC microswitches, not all teams do. A small minibot could be engineered very well.

2)Engineers solve problems to be effective and efficient. The problem at hand is triggering the target before the other minibots. If you are too busy trying to extend the lifespan of a $1.50 (more or less) switch at the cost of abandoning the overall goal, you are not engaging in good engineering practices either. If an NXT gets smashed you are out $150.00, for just 5% of that cost, you could replace a microswitch 5 times. In addition, the initial cost for a microswitch based system is about 0.6% of the initial cost of an nxt based system if you include the touch sensor and the motor controller. Thus, the most effective system in terms of how fast the goal is reached and cost is the small minibot. The big minibot just has too many disadvantages.

Re: Big Minibots
 

Destruction of material and risk taking IS part of good engineering, especially part of race engineering.

The competition is not about the team that builds the minibot with the least cost, most reliable parts that never degrade over the course of a season.

Teams spend many thousands of dollars per season and most of the parts depreciate in value very quickly most KOPs are replaced within a few years.

How much engineering maintenance does a NASCAR need compared to the family minivan?

Per mile, how much more often does a NASCAR fail as compared to a family minivan?

In reading the competition manual as a good engineer, are the requirements for the portion of the competition regarding the minibot more like NASCAR or like the family minivan?

Is it correct engineering to teach students to build a minivan for a NASCAR race?

There are plenty of relatively reliable 2.5-3 lb minibots.

If FIRST wanted the best teams to use the NXT and motor controllers, they should have make a challenge more like a use of a minivan- running all over town, picking up toddlers and groceries, making controlled stops, obeying all speed limits and signals, etc.
But then, who wants to go to a competition to watch that?
Probably not the stuff a Cirque du Soleil promoter could promote.

Has anyone had to replace a KOP limit switch from electrical overload in this challenge? What is the failure rate?
(Team 241 has used them without failure over 100 times.)

What is the perception of the other failure rates that the large minibot engineers have actual data to back up their concern?

Re: Big Minibots
 

If it's burning out halfway up the pole, it's safe to say they didn't engineer the thing - they just built it and prayed it would work. Complete burnout's like that would occur because the motor is operating in a red zone on the power curve, something that could have easily been avoided had analysis been done on the machine.

Re: Big Minibots
 

but wait, hold on a sec. I thought you said that speed was "wayyyyy" more important than survivability. So by your example,not sacrificing too survivability for speed is a good thing. Thanks for proving my point :-)

Be aware not everyone analyzes the game the same way. Don't be so bold as to say your analysis is better than someone Else's. We all come from different places and experiences. There needs to be more middle ground around here and not all this "i'm right and you're wrong" crap-o-la. It's getting a bit tiresome.

Re: Big Minibots
 

Hey... My team used the micro-switches also... But to call someone ignorant or lacking in a science background because they build a big minibot is just wrong...

The same logic, being "competitive", that permits switches to fail applies to allowing motors to burn up... That is assuming that all of you self righteous "engineers" actually considered the consequences of your actions... There are teams who "guessed" at the motor torque curves and others who used switches that "seem" to work... Is one engineering oversight less important than the other?

I prefer to think that any team who fielded a working minibot and delivery system should be praised and not looked down upon because they took a different path to the solution...

This can't be what FIRST is about...

I hope I have made my point and I will post no more on this subject.

Re: Big Minibots
 

My team used the switches also; I have to say that they work great, at least for the time being. I just wish that their application required them to be a bit more robust; we've already broken a few by crushing them.

Mike, a working minibot is a working minibot. No one reasonably doubts that that is a good thing to achieve. However, I think the point that people are trying to make, which may be confusing/rude some due to it's harsh language, is that it can be improved to be better at the goal it's trying to achieve. FIRST isn't about teaching kids to do it once, and then be done.

Re: Big Minibots
 

Any team that first worked on their own to try to design a minibot, understand the physics and math and the engineering specifications and then built it and experimented and refined it- has done great engineering instruction.- It's quite commendable and appropriate to spend long hours brainstorming and experimenting free from the din of other teams ideas.

In real engineering, when is not appropriate to understand the approaches of your competitors? In real engineering, customers don't want engineering teams that can just copy: they want a team that create ideas and throw away ideas and sometimes learn and improve from what they see from competitors. If you are heavily inspired from some other team's work, then spend the time to understand the physics and spend considerable time to improve on it versus just copying it.

We were not impressed by the reliability of the gearboxes: especially using the hubs directly on the wheels: after only a few times up the pole using about 10 lbs of normal force, the wobble seemed obvious that the gearboxes would not last a season's worth of stressful pole climbing.
The gearbox sounded inefficient and the speed of our pole climbs were approximately the same as those shown in the Kickoff video.
We saw smoke and lost a motor/gearbox that first week after we got the kit.
We lost a second motor on our bigger minibot (4.4 lbs) that uses the motor/gearbox after we got back from our first Regional.

It was partly the quest for reliability that led us to simplify and get rid of the gearbox. Less weight means less stress on the motors. Dynamometer results posted here on CD helped.

Is it good engineering not to network and know how good the competition is?

Because of the cross fertilization of ideas between teams, the robots at week 8 of competitions can be much stronger than those at the first week.
The question is: what should your team do with this wealth of information and ideas for solving the challenge? Should your team ignore it? Should your team understand how fast the competition is but not how?

These are not necessarily easy questions to answer.

Any mentor/volunteer willing to spend time and energy facilitating any of the physics lessons, the engineering design, the fabrication, or the testing, etc. is helping students immeasurably.

Many teams end up spending TOO much time redesigning their robot and school work or other aspects of life suffer. The key is balance and mutual respect.

Big ; little ; can't we all just get along?

Re: Big Minibots
 

We have a kind of medium sized minibot. I was not involved in designing/building it, we have a new mentor who took this on with several students. I think I would have done more research into how to eliminate or at least modify the Tetrix gearboxes, but the design we have did end up working well and won us a few matches. We had some depolyment issues during the heat of competition (the elimination rounds were really heated, compared to qualifying) and we also had a problem with the minibot where it didn't go up the pole all the way. We did find the loose nut that caused it, after a few failed attempts. The looks on the faces of the two young students who fixed it, and got us that win....just priceless....

Re: Big Minibots
 

In terms of physics, we would have loved to have made a lighter minibot with a better gear ratio. In terms of practicality,we worked on the KISS principle. KISS won over physics for us.

Our reason for making a big minibot was due to lack of experience and lack of shop resources.

Our team didn't have any experience with FTC before the kickoff. The minibot was built by a student who joined our team three weeks after kickoff and a parent who was a first year FLL mentor. Our minibot used the NXT, due to the mentor's knowledge of NXT programming and its sensors.

We are also working out of the garage of one of our mentors. We had to budget our usage of power tools for building the hostbot and minibot. Which limited the amount of tool time for the minibot team for making it faster.

I was amazed and pleased that we got a minibot working with the amount of experience and resources the two had before shipdate. Although we lost many minibot races with other teams, it was satisfying just to successfully launch the minibot.

Re: Big Minibots
 

That, Sir, is what this is all about. :-)

Re: Big Minibots
 

our mini bot is about medium size but the difference with ours compared to others at the bayou regional was that ours was deployed and went up 100% of the time and in the final round which our alliance was victorious it was literally the minibots that won the match had a great time at the regional hope to see the same teams and more next year seems like the mini bot slamming against the pole and not doing anything was a constant result for many teams

Re: Big Minibots
 

What I am beginning to see here is diversity not only in minibot size preference, but also in reasoning. Some people decided on small minibots for simplicity or reliability, and some people chose larger minibots for the same reasons. The motives might have been budget, durability, speed, or "because this is what we know how to do," but it doesn't really matter all that much in the end. Teams are settling into their comfort zones. Teams chose to build their minibots as big or as small as they are because that is what the individual team has found to work best for them. It fits their unique needs and priorities of the team most effectively for the resources and know how available. That is the answer to the OP's question.

Quod erat faciendummaybe...

Re: Big Minibots
 

At regionals: any minibot large or small is better than none.

A reliable minibot that will last the whole regional is better than one that fails every 2nd match.

It's rare to see a match where all 4 minibots are deployed let alone reach the top of the pole. Reliability matters more than speed (at regionals).

Early Friday Seattle, it was clear having a working minibot & deployment system was a match winner. Late Friday it was becoming clear that a "good" hanger robot was better than a minibot.

At championships, it'll be different - everyone will have working minibots, everyone will have working robot manipulators.