20-03-2011 09:56

Jim Wilks

Re: pic: One-day Minibot

Looks Great!

Any details on the switch at the top?

JW

20-03-2011 10:11

DonRotolo

Re: pic: One-day Minibot

It takes a whole day to reach the top? I think that might be too slow

20-03-2011 10:22

Chris is me

Re: pic: One-day Minibot

I'm very surprised that this minibot took 1.6 seconds to go up. My guess says it should go up in about 1.2.

Good job with the minibot. I expect this on every robot by the end of the year...

20-03-2011 10:36

PhilBot

Re: pic: One-day Minibot

OMG... I started building that exact same robot yesterday.

My design had the magnets above and below the rollers as I didn't know if your configuration would provide enought vertical allignment. I even have that same top switch from Lowes.

I see that you have a limit switch to turn the bot on when it contacts the pole. I was planning to turn it on as it left the robot, but your's is probably more universally interchangable.

Too Cool.

Phil.

20-03-2011 10:38

Chris is me

Re: pic: One-day Minibot

It may be worth it to spin up the robot before you touch the pole. Play around with it and find out

20-03-2011 10:50

jvriezen

Re: pic: One-day Minibot

One of our early minibot designs had magnets above and below drive wheels but we found that if deployment wasn't good, the bot would attach with one magnet in contact with the pole, which works very well at increasing friction and helps in the production of smoke signals. Putting the magnet between the rollers assures there is no way the magnet can touch the pole.

John Vriezen
Team 2530, "Inconceivable"
Mentor, Drive coach, Inspector

20-03-2011 11:06

VKP

Re: pic: One-day Minibot

What material did you use for the rollers? It looks like some sort of rubber. Did you take it off of the Tetrix wheels? Or is that electrical friction tape?

20-03-2011 11:14

JB987

Re: pic: One-day Minibot

He said 1.6 seconds from the base. Maybe he is referring to time it takes from breaking the plane at start of deployment to the trigger? Anyways, this looks much like our new iteration. Wonder if he left the pinion on and used set screws not visible from the front view to hold or if this is a straight press to the motor shaft. Nice work.

20-03-2011 12:38

BIGWILLI2081

Re: pic: One-day Minibot

how did you connect the motor shafts to the bigger shaft?

20-03-2011 12:41

216Robochick288

Re: pic: One-day Minibot

Honestly, you don't even need the magnets. you could go a similar design with PVC that is just slightly bigger than the diameter of the pole then cut about 60 degrees out of it to hold to the pole with the motors under... its a brilliant design. Simple too.

20-03-2011 13:07

TEE

Re: pic: One-day Minibot

can't see the battery

20-03-2011 14:28

VKP

Re: pic: One-day Minibot

Our team began making a minibot like this. We took the Tetrix axles and used a lathe to bore a hole in them the diameter of the motor shafts, and then press-fitted them on.

20-03-2011 14:54

undefined117

Re: pic: One-day Minibot

I have found that magnets make the minibot slower becuase they add friction, If you have any extra time you may want to work on getting some pvc to snap onto the pole. Our minibot can get up in 1.2-1.3 seconds.

20-03-2011 15:04

Nikhil Bajaj

Re: pic: One-day Minibot

Just a note: you are correct in stating that the magnets can potentially add to the damping in the system and slow the mini-bot down. However, this is not friction, unless you are rubbing the magnets or something else on the pole.

http://en.wikipedia.org/wiki/Eddy_currents

This is a very common high school physics class demonstration, taking a vertical aluminum tube and sliding a magnet down it towards the ground. It can take longer than one would expect.

20-03-2011 15:51

sanddrag

Re: pic: One-day Minibot

Thanks for all the compliments. This was more an experimental project, to prove a point to myself, rather than anything else. The point I wanted to prove is that this is very easy and simple to make, and works well. You may or may not see this on 696's robot. In either case, it'll be at Long Beach if anyone wants a look. I'm also thinking, maybe I could come up with something simple to be able to add this onto any alliance partner robot that doesn't have a minibot. Not sure how that would work with inspection though.

I fully expect many winning teams to have something similar, but it will have been much refined beyond what this is currently. I don't plan to do any further work on this, however there is a lot of room for improvement. There's probably .2 to .3 pounds you could easily take out of it, and you could cleanup the wiring, and optimize the roller diameter.

Anyhow, let me answer a few questions.

It's made for a household lamp or light fixture, and was purchased from a local hardware store. It's a push-button on-off type.
Yeah, it was a little slower than I expected too. My first try, on a dead battery, produced a little smoke from the motors. They still appear to work fine, however, they may work better if they had never smoked. Also, the acceleration is a lot slower than I would have imagined.
This is exactly the idea. There's some friction that results from it, but I'm satisfied with a sub -2-sec climb.
It probably would. However, I'd be somewhat worried about wear on the "tires." Anyhow, the present state is as far as I'm going with this design.
This was the idea. I'd estimate there is about .045" between the pole and the magnets the way I have them mounted.
Black latex tubing.
It's 1.6 seconds from right next to the pole, right above the base. I did not account for deployment time.
There are no set screws. The pinion gear was removed from the motor, and the shaft was drilled and pressed directly on. Unfortunately, one thing I did not consider is there is no really good way to remove the shaft from the motor, if you ever have to. So, for spare motors, you'd want spare shafts already pressed on.
It sits on the back side of the C-channel. There's a small piece of aluminum angle on the bottom of the C-channel that it sits on, and Velcro on the whole back of it holds it on. Zip ties would work too.
The magnets provide approximately 6-6.5 pounds of force to the pole. It's more than enough to let it drive upside down on a horizontal pole. You could probably get away with using less magnet force, but I wanted to be absolutely certain it stuck. Not sure how much magnet damping force results from this setup, but I imagine it's not much.

One other interesting thing to note, is I mounted the magnets with aluminum screws. I'm not sure if this would provide more or less force to the pole, as compared to steel screws. Anyone care to answer that?

20-03-2011 16:22

SGS

Re: pic: One-day Minibot

How did you get the gearboxes off the tetrix motors?

20-03-2011 16:37

sanddrag

Re: pic: One-day Minibot

With a small Phillips screwdriver.

20-03-2011 16:58

Chris is me

Re: pic: One-day Minibot

You'll also want a nut buster for the pinion.

20-03-2011 17:37

Jeffy

Re: pic: One-day Minibot

How is the plate for turn-on connected to that switch?

20-03-2011 17:50

Travis Covington

Re: pic: One-day Minibot

Did the teams who you drew inspiration from have any issue with you posting this?

20-03-2011 17:52

AdamHeard

Re: pic: One-day Minibot

I would assume so.

20-03-2011 17:57

Richard Wallace

Re: pic: One-day Minibot

Why?

20-03-2011 18:02

Vikesrock

Re: pic: One-day Minibot

Each of the teams listed has competed at least once already. Their minibot designs are "in the wild" (118's and 148's were featured in videos shortly after ship). I really don't see any reason why permission would need to be sought from any of these teams to post a picture of a minibot inspired by their designs.

20-03-2011 18:06

Travis Covington

Re: pic: One-day Minibot

"In the wild" is up for interpretation. I know at least two of the teams mentioned aren't thrilled with this unveiling.

20-03-2011 18:16

Vikesrock

Re: pic: One-day Minibot

I could tell that by you asking the question. I find it somewhat bizarre that these teams think that there was any way that this minibot design was going to stay "under wraps".

This is not the first, or even the second place I have seen this design, it is the third. I have a picture of 1625's minibot from Wisconsin and I saw 2415's in person at Peachtree this weekend. Both the picture and in person looks gave me sufficient information to build a similar minibot without much trouble.

Judging by the post by Chris is Me, this minibot design is circulating around New England as well.

The nature of the minibot task is such that by Champs many minibots will be very similar. Instead of spending time posting about people copying it, your time may be better spent optimizing both minibot and deployer to get every last tenth you can. I don't like it either, haven't since kickoff, but that's just the way it is.

20-03-2011 18:19

Steve_Alaniz

Re: pic: One-day Minibot

xx

20-03-2011 18:57

1708xMr.Roboto

Re: pic: One-day Minibot

Gracious Professionalism, that is all.

20-03-2011 19:06

AdamHeard

Re: pic: One-day Minibot

Is it unGP for a team to be upset by someone else publicly posting their design?

20-03-2011 19:06

Tom Ore

Re: pic: One-day Minibot

1986 also used this same minibot design. They even posted some specs from it in another thread.

20-03-2011 19:10

XaulZan11

Re: pic: One-day Minibot

I can understand how you can be upset if you see pictures online of a similar design that you spent a lot of time working on. But, if you attended a public event (where everyone and anyone can see your robot and take pictures of it), I don't think you can complain if someone talks about your design or even posts pictures of it on a public website. It's just a nature of the beast.

20-03-2011 19:12

548swimmer

Re: pic: One-day Minibot

I think the issue is with someone else posting their design. If the team wanted their design revealed, they would have posted it themselves.

20-03-2011 19:13

1708xMr.Roboto

Re: pic: One-day Minibot

If I understand correctly, this design was built by the original poster. As he mentioned it was inspired by a few other team's designs, but he gave them their credit as it was due. It may apprear to be the same, but it's not exactly the same, which makes it the Op's design.

20-03-2011 19:15

Basel A

Re: pic: One-day Minibot

I think he's suggesting it isn't gracious to essentially post another team's design..

Anyway, I think so many minibots at this point have such similar designs that he could have been inspired by quite a number of teams, some who wouldn't be upset at all. At this point, as someone mentioned, it's worth more to optimise than to express dissatisfaction with loose-lipped miniboteers.

20-03-2011 19:18

548swimmer

Re: pic: One-day Minibot

Agreed! This design is "inspired" by our back-up minibot. Oh wait... we never used that minibot, or even brought it to a competition....

20-03-2011 19:29

Travis Covington

Re: pic: One-day Minibot

We're happy to share our design philosophy, design decisions, and the processes we used to get to our current solution. We do hesitate, however, to post detailed pictures and designs of things during the current season to both ensure learning takes place, but also to maintain a competitive advantage. Ask any team and they'll tell you we're the first to explain all about our robot design and any details about it.

The bottom-line is that we're happy to give you the tools you need to build a successful mini-bot, but prefer doing so in a way that further enables you later. We must also not forget that this is a competition. The unfortunate thing about this year is that the simplest mini-bots will be the most successful (and the easiest to copy). When a significant majority of some of the early regionals could have been won with a single first place mini-bot, their importance cannot be over emphasized. Copying, sharing, posting pictures or detailed CAD of other teams robots without their consent is neither inspiring nor should it be considered GP.

While our issues here are not really that big of a deal, the benefits and takeaways from this thread could have been achieved through a different and more discrete means.

20-03-2011 19:35

Teched3

Re: pic: One-day Minibot

I personally don't like to have to make shafts for all the spare motors, especially for these motors and the task at hand. I try to use motors as they come out of the box. Replacement is much easier. We use double set screws with a Loctite adhesive that is advertised for polycarbonate. In addition, since the motor shaft does not come through the back of the motor, you risk damaging the rear bushing pressing your drive shaft onto the motor shaft. If you still insist on removing the pinion gear, I suggest making a push plate that will go in the area between the back of the pinion and the front of the motor housing. However, you still have the problem pushing the drive shaft onto the motor shaft. I would rather use that same push plate to press the drive shaft directly onto the pinion gear.

Nice design - quick build and effective. However, by St. Louis, consistency with deployment and dependability are likely going to be the deciding factors. You can only lighten so much, push the amps only so far, before you plateau with the minibot design. We're saving our best for St. Louis.

20-03-2011 19:37

sanddrag

Re: pic: One-day Minibot

It's a special type of limit switch that I had a few of sitting around. The little plate is spot-welded on, from the factory.

To clear up any confusion, I'd like to explain my thought process behind this design. I find it silly I need to defend myself here, but nonetheless, here's my response.

If you look at the Russian Buran shuttle, many people would claim they stole it from the United States, when in fact, both countries had done proper engineering and arrived at very similar conclusions, independently.

When I built this, I did not have any pictures of any other teams' minibots with me. Interestingly enough, I have never even seen up-close the minibots of the teams of individuals in this thread who have taken issue with me posting this design. Yes, I saw the general concept of the fast minibots at San Diego. But so did hundreds of other people watching in the stands. This minibot design is a logical conclusion of proper engineering and physics principals. To think that anyone with an understanding of such principals would not arrive at a similar conclusion is preposterous. It is not an optimal conclusion, nor the only conclusion, but is is certainly a logical one. I don't think anyone with an understanding of physics would disagree.

From the minute the rules came out that said you couldn't launch the minibot, and all that was required was a motor and a battery, that's all that I wanted to send up the pole (well, two motors, more power). Why have mass you don't need?

Physics principals say less mass makes for less force (weight) which makes for less work and a shorter time to complete the work, if the available power is fixed (which it is). I'll post a writeup on this in a separate thread. And of course, to be realistic, you need something to provide a frictional force to the pole (for propulsion), you need a switch to turn it on, a switch to turn it off, some means of providing normal force to the pole, and a "stick" to hold it all together. WHY any team would choose to send more than this up the pole is beyond reasoning. They clearly do not understand the physics involved. So, that's how this design came to be. What is the least amount of "stuff" we can send up the pole. I've been saying this since day 1.

Regarding removing the gearheads, I had been looking for data since Day 1. At some point, CD user Richard was gracious enough to stick a motor on a dyno, and post the results. Anyone who read these results would have concluded, the gear-head needs to come off. And hence, a smaller "wheel" follows, additionally reducing mass.

I hadn't worked on the minibot much at all for the build season. I had many ideas of how it should be, but I never got around to doing anything about it. I was too busy with work, personal projects, and other parts of the robot. Our team has a culture of letting the students go their own way, letting them fail, then learning why the failure occurred. It's not a culture I agree with, but it's how we do it here. Anyhow, we had several new freshmen students working on a minibot the whole season. They built a large, heavy minibot. Clearly they didn't understand the Physics involved, nor had they done any math on it. It's slow, and difficult to deploy. However, my students did not understand what was deficient about their design. So, I decided to build this to prove a point.

As a team, we went to San Diego to watch the regional, and see what works and what doesn't. Clearly, small light minibots work. So, I embarked on an endeavor to see how quickly I could build one, for my own amusement.

I dug around through about 200 lbs of scrap metal, found a piece of C-channel, looked at it, and thought "hmm, this might work"

I went to 3 hardware stores, looked at every type of switch they sell, picked one and thought "hmm, this might work"

I looked at the rules and thought "what allowed materials can I use for tires?" I saw latex tubing on the list and thought "hrmm, this might work"

I opened a web browser and started searching for strong magnets. After an hour or so of searching, I found something cheap that looked decent and thought "hrmm, I have no idea if this'll work, but it's cheap enough to try."

As for an on switch riding against the pole, that's already an idea we'd had for many weeks.

But, I don't see any point in debating who came up with what ideas first. The winners will be the ones who have refined their design, which I have not.

On the topic of sharing designs. When I was young, and not-well informed about how the good robots work so well, and how the good teams do what they do, I learned from Chief Delphi. I learned not by constant wonder, and frustration, but by abundant sharing, and examples graciously provided by others. At events, I learned how things work by people showing me up close. The reason I've posted what I've come up with here, is for the teams who maybe don't have a physics teacher or engineer to help them, or for the teams who maybe got down such a narrow path of thinking, they never considered something like this.

Some will choose to copy the design. But, I don't feel I've given anything away. Engineering is no secret, it's math. I could have not posted this. That's always a choice. But who does that benefit? Perhaps a select few who were hoping that nobody else could do the math (which Ether has so kindly posted here on CD, for all to benefit from). What is the greater good?

This is something anyone who can do a little math can figure out. It's something a dad with tools in his garage can build. However, the winners will be the teams that can iterate and refine their designs to the least mass and optimal performance.

20-03-2011 19:43

sanddrag

Re: pic: One-day Minibot

I did exactly that to remove the gear. Did it years ago with FP motors too. I never considered a press plate to push a shaft directly on the gear, without loading the motor shaft. Great idea! I'll have to keep that one in mind.

I was a little worried about pushing the shaft, when it doesn't go all the way through the motor, but it appears to have turned out okay.

20-03-2011 20:04

Tom Ore

Re: pic: One-day Minibot

Studying and understanding successful designs is an excellent way to learn. The students who spent time on their own team's minibot will learn a great deal when they see a design that is much faster than they came up with. They will begin to understand where their thought process was limited and maybe will know a bit more about how to approach the next problem that comes along. The students on our team spent about half the build season working on versions of the minibot with the NXT Brick as part of the minibot! When we got to KC, our minibot was only a 2 second minibot. However, our deploy system works pretty well and we won KC with that 2 second minibot. (Information on our robot including deploy have been on our team's website since the end of the build season so if you're looking for deploy ideas feel free to go there.)

20-03-2011 20:19

Travis Covington

Re: pic: One-day Minibot

I don't disagree with that, but do feel that an explanation of the reasoning behind design decisions will almost always result in a more thorough understanding of the solution than analysis alone can obtain.

20-03-2011 21:19

Steve_Alaniz

Re: pic: One-day Minibot

xx

20-03-2011 21:45

Travis Covington

Re: pic: One-day Minibot

The specific details of the interactions were not posted here, nor do they need to be.

I do not disagree with the spirit or intent of the post, and have a long history with Dave personally and did not intend to discredit his teaching or work. I said what I needed to say, and it seems that we are in agreement over a good majority of everything else. However, as far as simplicity and logic are concerned; the simplest solutions are sometimes the ones requiring the most iteration, refinement, and time. The designs that make you say "Why didn't I think of that?" are usually from the people who thought of everything else, designed it, built it, had it fail, and then iterated until they were successful. Logic and reasoning don't always translate into simplicity, even when keeping minimalism in mind.

20-03-2011 22:44

Mr V

Re: pic: One-day Minibot

There are pinion pullers designed specifically for removing pinions. Pulls it right off easily w/o and damage and only costs a few dollars. However we removed them a couple of different ways w/o any damage to the rest of the motor because we didn't want to wait for the mentor who had the pinion puller at home. The simplest method to do it w/o a pinion puller is to cut a slot slightly wider than the shaft in a plate that is larger than the motor. Then slide the motor on the plate, support the plate with the open jaws of a vise or some blocks and use a small diameter drift to drive the motor out of the pinion. Be sure to have someone ready to catch the motor. Grinding or filing the pinion most of but not all the way to the shaft will allow it to slide off easily also.

No worry about pressing the new "wheel" on the shaft when I did autopsy on motors with broken tabs and burnt inductors I found out that the CE bushing is a ball end type bushing fully supported by the brush plate. So as long as the amount of force is not great enough to bend the motor shaft and you support it on the bushing bump on the brush plate and not the case or terminals the motor shouldn't be damaged.

21-03-2011 00:03

Bill_B

Re: pic: One-day Minibot

Is there an A in Q&A that tells us definitely that the pinion is not part of the motor? There has been a lot of traffic about pressing things onto the motor shaft, but I don't recall anything about the pinion being a Tetrix part and thereby modifiable.

21-03-2011 00:07

Steve_Alaniz

Re: pic: One-day Minibot

xx

21-03-2011 09:05

JesseK

Re: pic: One-day Minibot

If teams wanted to keep their designs 100% totally secret, even on the field, they could have spent an ounce or two on non-functional decorations. Who knew what the kickoff minibot's design was until it was examined via a photo posted after kickoff? Strategically, that's a hard call though. Do you risk negating the full effectiveness of the design for design longevity over 8 weeks?

It's always easy to build something you have a good sense of where to start. It's why IP laws exist in the first place. It's also why the powerhouse teams will still probably kick our butts in weeks 1-2 next year.

21-03-2011 09:11

thefro526

Re: pic: One-day Minibot

R47-A covers the removal of the pinion - if you consider the pinion to be a part of the motor.

Personally, I don't believe that the Pinion is an "integral part" of the motor, since removing it doesn't change how the motor works...

21-03-2011 10:17

Bill_B

Re: pic: One-day Minibot

I read <R47A> several times, too. I think that the modifications allowed by it relate to the attachment of the motor to the robot or the shaft attaching to actuated part. So if the pinion is part of the motor shaft then, OK by r47a. In the case of the Tetrix motor, there is a bracket to which the gearbox is attached. Part of the gearbox? or motor? Maybe it doesn't matter, since modification of it is allowed to change attachment of the motor to the robot. I don't think that the pinion is part of the attachment of the motor to the robot, but it is part of the attachment to the actuated part.

The blue section below <R47> outlines the intent of forbidding structural modification. I'm really not trying to be pedantic, but if removing the pinion didn't change how the motor "works", then why do it? weight reduction? That is my opinion of course, and we all know how influential personal opinions are at the inspection station, right?

23-03-2011 10:15

Al Skierkiewicz

Re: pic: One-day Minibot

Guys,
1) In a world where everything is open, reverse engineering is capable. There is no way that anyone can consider that their minibot design is not going to be copied in part or in whole by another team. This design is in fact used in some iteration over the whole country thus far and in no small way mimics the design of one of the minibots used for demo at the kickoff. Why do you think magnets are in the allowable materials list?

2) Removing the motor pinion is an allowable modification. It has been since at least the first Fisher Price motor was provided in the KOP.

3) The push/push switch at the top of the minibot must be labeled as a "light switch" or at least marketed as a light switch to be legal. If it is merely in the same area of the store where there are light switches is not enough to classify this as a light switch. The GDC has ruled that even if certain manufacturers use it as a light switch in an appliance you can buy, it does not make it a "light switch". Be prepared to show documentation.

23-03-2011 10:28

thefro526

Re: pic: One-day Minibot

Al, I was able to find an identical switch to the one that Sanddrag is using at a local hardware store. On the packaging it mentions "For use on Lamps and Light Fixtures". I'd imagine that line would make it legal.

23-03-2011 10:46

IKE

Re: pic: One-day Minibot

http://www.chiefdelphi.com/media/photos/36731?

So is a "Lamp", a "Light"?

Just happened to have a pic on my phone for some reason... Will the GDC comment on pictures? I know they won't comment on specific designs.

23-03-2011 11:38

PhilBot

Re: pic: One-day Minibot

I've never met one that wasn't.

23-03-2011 15:20

Akash Rastogi

Re: pic: One-day Minibot

Yessir it is. A couple of our teams have been collaboratively working on minibot design since the beginning of the season. Slowly but surely we all also came to the same conclusions in design as 254 etc.. (or at least we think we have because we're all running similar speed minibots).

Our group of teams would like to thank 1625 and Richard's post about the Tetrix motor specs for initial design inspiration. Anything after that has been under our own development and we have all accomplished 1-1.5 second minibots.

I'm surprised we're still seeing the "who inspired what" debates especially after sanddrag pretty much explained what most teams who came to this minibot design went through.

Thanks for your insight in your own design sanddrag! It is the very same engineering process we went through. The big issue we were having was the light switch we found (which thankfully Al said is legal! ).

Now onto making deployment faster

23-03-2011 15:29

Chris is me

Re: pic: One-day Minibot

40, 177, 190, and 2791 all had variations of the direct drive minibot at WPI. 2791's design was a combination of at home engineering with some helpful tips from 816 to save us a few iterations.

Who knows how many teams will have them at later events? We certainly showed off our Revision B to a few dozen teams there.

We are using lessons learned at that regional with some "inspiration" from other teams to work on a further revision. We are not copying directly, just using others as a starting point.

23-03-2011 15:52

thefro526

Re: pic: One-day Minibot

Sometimes it seems that people forget that teams outside of the "Elite" tier often share information as well. We might not have the resources to reach the conclusions on our own, but after enough combined failures from the 5 or so teams involved, we seem to have something that works.

23-03-2011 16:47

James Tonthat

Re: pic: One-day Minibot

Our team got a lot of help from Dustin when he shared with us his backpack man design. We improved upon it, made a better clamp system, did some electronics voodoo magic and it helped win us a regional.

23-03-2011 17:08

billbo911

Re: pic: One-day Minibot

I love electronics voodoo magic. It makes things work so much better!

23-03-2011 17:18

sanddrag

Re: pic: One-day Minibot

<R92-AA> Did you mean to say "aren't" ?

23-03-2011 18:03

Al Skierkiewicz

Re: pic: One-day Minibot

Nope, magnets are allowed for use on minibots.

23-03-2011 18:18

Jim Schaddelee

Re: pic: One-day Minibot

Inspired by this thread I made a new mini bot in a day. Its different then what I have seen so far. How are people calculating there times. For example , Is this a 1.4 0r 2 sec mini bot? The bot weights 2.29lbs

http://www.youtube.com/watch?v=oMXnV...er_profilepage

23-03-2011 18:37

Ether

Re: pic: One-day Minibot

Can't tell. You gave it a push.