pic: One-day Minibot

[undefined117]

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.

[Nikhil Bajaj]

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.

[sanddrag]

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.

Originally Posted by jgw

Any details on the switch at the top?

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.

Originally Posted by Chris is me

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.

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.

Originally Posted by PhilBot

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 yours is probably more universally interchangeable.

This is exactly the idea. There's some friction that results from it, but I'm satisfied with a sub -2-sec climb.

Originally Posted by Chris is me

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

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.

Originally Posted by jvriezen

Putting the magnet between the rollers assures there is no way the magnet can touch the pole.

This was the idea. I'd estimate there is about .045" between the pole and the magnets the way I have them mounted.

Originally Posted by VKP

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?

Black latex tubing.

Originally Posted by JB987

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.

It's 1.6 seconds from right next to the pole, right above the base. I did not account for deployment time.

Originally Posted by BIGWILLI2081

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

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.

Originally Posted by TEE

can't see the battery

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.

Originally Posted by Nikhil Bajaj

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.

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?

[SGS]

How did you get the gearboxes off the tetrix motors?

[sanddrag]

Originally Posted by SGS

How did you get the gearboxes off the tetrix motors?

With a small Phillips screwdriver.

[Chris is me]

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

[Jeffy]

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

[Travis Covington]

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

[AdamHeard]

Originally Posted by Travis Covington

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

I would assume so.

[Richard Wallace]

Originally Posted by AdamHeard

I would assume so.

Why?

[Vikesrock]

Originally Posted by Travis Covington

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

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.

[Travis Covington]

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

[Vikesrock]

Originally Posted by Travis Covington

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

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.

[Akash Rastogi]

Originally Posted by Vikesrock

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

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

[Chris is me]

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.