Re: Minibot climb rate
 

What method do you use keep the bot from falling off the pole?

Re: Minibot climb rate
 

if the mass if distributed left and right and the angle of the bot as it climbs the pole adjusted to account for top to bottom weight distribution (hang the minibot from a string and check the angle it wants to hang and almost duplicate that) it will just climb straight up. Ours did that though we did add a small cross-section of a pvc pipe to make it fall straight.

HTH

Re: Minibot climb rate
 

Am I right in assuming that you are using a wheel on each side of the pole, with the battery on the same side as one wheel, so that you're using torsion to lock the minibot 'on'?

Re: Minibot climb rate
 

I've never seen your bot so I cannot quite picture what you are describing.

I guess what I was asking was do you have some sort of snap-action device that springs shut and locks the bot to the pole, or do you "press-fit" the bot to the pole, or some other method?

Re: Minibot climb rate
 

Close - we did have a wheel on both sides but the weight was even left and right but the bottom (below the wheels) was heavier than the top (above the wheels). We launched it with the wheels at a 45 angle, it pulled itself onto the pole (righting itself in the process) and then fights (a little, maybe 2 or 3 degrees) against the cantilever on the way up. We depended mostly on flex in the motor mounts and sticky wheels to create the rolling friction against the pole.

HTH

Re: Minibot climb rate
 

Press fit is the best description, flex in the motor mounts and sticky wheels created most of the rolling friction. We used a small cross section of PVC but that was needed to make it fall straight down

http://flic.kr/s/aHsjuentrP

Re: Minibot climb rate
 

See attached JPG.

1) The rollers look angled. Is that intentional?

2) It seems like the weight of the battery pack (2) would cause the bot to fall away from the pole in the direction indicated by the "->" arrow (assuming that the picture is right-side-up) ?

3) Is this part of the minibot?

Have you burned up any Tetrix motors with this configuration?

Re: Minibot climb rate
 

1) They do look a little angled. The frame must have bent some last time it came down, it is quite thin. They are supposed to be normal to the plate everything is mounted on.

2) Indeed it would if you did not tilt it fwd a wee bit, which means we are sacrificing some power I know but it was still quite fast

3) Yes, we had a slower minibot (very reliable) which launched from a 45 degree ramp and we wanted to use both minibots interchangeably. That is the only purpose for that piece of the assembly.

We burned up one motor after running it up many dozens of times during testing but that motor smoked some while testing an interim design so it was a little suspect.

We tried button magnets but this configuration seemed to work better. Perhaps a nicer shaped magnet would have worked better, maybe we'll try it before the off-season events.

HTH

Re: Minibot climb rate
 

I never would have guessed when I started this thread that it would have grown to 220+ posts. I also didn't consider one thing, this is FIRST. When I did the very first rough calculations, I had to make a lot of assumptions. My first guesstimate of climb time was in the ball park of 7 seconds. I should have known that the envelope would definitely be pushed, heck, almost to the breaking point.

The first minibot we built was very reliable and won a lot of races. It is not fast, just reliable, 4.5 seconds consistently. We rode that little bot all the way to the finals in Sacramento. It will be with us in St. Louis and be available for any team that needs it. It will have a deployment plate with it already set up, all that is needed will be a set of rails to send it out on and a battery. Her name is Miracle.

Now, just so you don't get confused, Miracle still works just fine, but we on Eagle Force don't like to sit by when we know we can do better.

Meet Miracle 2 v2.1a.


Miracle 2 v2.1a was inspired by a post by Sanddrag, along with several other designs we have seen.

When we originally set out to build a new mini to take to St. Louis. we were shooting for a sub 2 second mini. That is a far cry from the first estimate I made of ~7sec. way back when this thread started. So how does Miracle 2 v2.1a perform? Lets just say, < 1.2sec is pretty darn close to acceptable.
There is one issue we still need to solve, see if you can identify it.
http://www.youtube.com/watch?v=nvXV8_8UQGk

BTW,
I have this Minibot all set up in SolidWorks. There are a couple minor items missing from the CAD, like the nylon screws, but otherwise, it is fairly complete. If you want a zipped version of the project, just shoot me a PM.

Re: Minibot climb rate
 

Wow, that's a pretty frightening suicide leap. Maybe adding a couple magnets would help rectify that.

Re: Minibot climb rate
 

Looks awesome. We have several videos with kids making sure to catch the minibot after hitting the plate. Our solution was a piece of PVC a bit larger in OD to the pole cut to around 200 degrees so that the chaotic "landings" were minimized.

Re: Minibot climb rate
 

Well, the plan for us is to reduce weight even more, not add more. So, we are going to try a little physics first.

As far as we can tell, the battery is the main issue. It's momentum is causing the back of the mini to continue moving up, even though the frame has stopped against the top plate. To remedy this, we are going to flip the battery over and move it up until it is parallel with the top of the frame. That way, it has no where to travel once contact with the plate is made. (If that isn't enough energy into the sensor to trigger it, nothing will be.) Maybe some padding on top will help as well.

Re: Minibot climb rate
 

What is the diameter and material of those wheels? That sucker is quick!

Re: Minibot climb rate
 

The axles are .375" and made of Polycarbonate. The tires are a silicon based surgical tubing material.

If you notice, this thing is accelerating almost the entire time. With slightly smaller axles, say .036", it might accelerate a bit quicker, but could reach max velocity too soon and increase the overall time to climb. The only way to tell is to try it, and we are happy right where it is.

From my experience with R/C car racing, I find the best approach is to be accelerating all the way until just before you start the next turn. In this case, that point is the top of the pole. So, it looks like this design is pretty close to optimal with the weight we currently have. Reducing the weight further will only improve things.

Re: Minibot climb rate
 

Minibot suicide is only one of the concerns about that leap -- the other is human safety. UL Safety Advisors at MSC made pit announcements, and distributed printed notices, requiring the use of gloves to catch minibots that regularly fell from the many practice poles teams had brought. That safety guidance is wise; at two events, I saw students in the first-aid stations being treated for bad cuts they had sustained by trying to catch falling minibots.