Sumo Bots B/C [Trial]

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Sumo Bots B/C [Trial]

Postby Jim_R » August 17th, 2009, 1:42 pm

Discussion for Sumo Bots B/C, a trial event in New York and Nationals.

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Re: Sumo Bots B/C [NY Trial]

Postby fmtiger124 » August 21st, 2009, 5:47 pm

Well, I didn't do this event last year, but some sort of wedge works best--along with a car that doesn't move to fast so you don't accidentally drive outside the ring
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Re: Sumo Bots B/C [NY Trial]

Postby inycepoo » September 15th, 2009, 7:30 pm

hey guys. i'm new to all of this robot stuff...so.
the old one from last year runs on vex...which is decent yes, but i dont think i can deal with such weak but okayish light motors for this year.
any suggestions what motors or other stuff from what brand to get?

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Re: Sumo Bots B/C [NY Trial]

Postby jadeboy » November 12th, 2009, 11:56 am

Wait a sec ... my school isn't offering sumobots this year :!: What's up :?: :?: :?:

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Re: Sumo Bots B/C [NY Trial]

Postby Skyline1010 » December 26th, 2009, 7:28 pm

The increase in size combined with a decrease in max weight is making it pretty tricky this year...that and the 14.4v battery limit. I've got a good bot going though...we'll see what happens

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Re: Sumo Bots B/C [NY Trial]

Postby gh » December 27th, 2009, 2:13 pm

I thought it would make things easier. Last year, I found the design pressure to pack as much stuff into as little area as possible a real challenge. I figured, if everyone else is also allowed to have 2.5kg within 300mm×300mm, then somewhere out there somebody has packed that much motor, battery, and wheel into their design. So to be competitive, I reasoned, I had to have that much in my design.

That more or less explained why I had to have 550-sized motors, special compact wheels, and a battery with the output equivalent of something like a motorcycle battery.

Since my site hasn't been linked to yet in this topic, I'll do it now: http://www.geekshavefeelings.com/projec ... -2009.html

In there, I explain design decisions (wheel placement, height, number of wheels, etc.), list history, and illustrate with videos of matches pictures of the bot.
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Re: Sumo Bots B/C [NY Trial]

Postby Skyline1010 » January 1st, 2010, 5:43 pm

Oh, I remember that bot from NY States last year. I beat it a couple times and eliminated it, but the design is pretty sweet nonetheless.

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Re: Sumo Bots B/C [NY Trial]

Postby gh » January 3rd, 2010, 4:11 pm

Oh hah, the thing was just about unusable by the time I was using it for competition. The transmitter was physically broken—one stick was loose and didn't return to center, and I swapped out a better motor controller after it shorted (heatsink touched a FET's leads, I think) and parts of the bot actually caught fire. Plus, I kind of stopped caring about SO by the time states was around. :\
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Re: Sumo Bots B/C [NY Trial]

Postby LukeThomas » January 3rd, 2010, 6:47 pm

I just hope some jerk event supervisor confiscates batteries because they charge above their label, It happened in the Midwestern NY regional, their battery pack said 18 volts but read 19, the battery pack were not allowed in competition
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Re: Sumo Bots B/C [NY Trial]

Postby andrewwski » January 3rd, 2010, 11:08 pm

I wouldn't have disqualified that. While it's true that you can overcharge a battery somewhat beyond the manufacturer's specifications, I don't think any team would benefit from doing so. It would be potentially dangerous while charging and would decrease the battery's life.

If the battery was labeled 18 volts and read 24 that'd be different, as there obviously would be something fishy going on, probably a swapped label or something.

But batteries are often labeled with a large tolerance, especially when fully charged. If you measure a new AA battery, it's going to read more than 1.5 volts.

The competitors should have shorted the battery until it was under 18 volts and then it would have been legal to use.

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Re: Sumo Bots B/C [NY Trial]

Postby fleet130 » January 4th, 2010, 1:40 am

their battery pack said 18 volts but read 19, the battery pack were not allowed in competition
When fully charged, virtually ALL batteries have a voltage greater than their nominal value. The rules are trying to get away from the need for event supervisors to measure the voltage. Someday someone will invent a "smart pill" that will instantly instill common sense into their behavior. Until then, you'll just have to "bite the bullet". At one point in the distant past, buttons with a picture of a bullet and the caption "I Bit" were popular.
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Re: Sumo Bots B/C [NY Trial]

Postby gh » January 4th, 2010, 10:27 am

For reference, NiCd and NiMH rechargeables, which most teams will be using, are 1.2V per cell but they should be charged to 1.5V each. Thus, a 14.4V pack of 12 cells ought be 18V when charged. Also, the more common lithium cells are 3.7V each, but are charged to 4.2V per cell. In fact, that is how they're meant to be charged: constant current is directed into the cell until a set voltage is reached, and then a constant voltage (in this case, 4.2V) is applied to the cell until the charge current approaches 0. This is called CCCV charging, and it's used for a lot of types of batteries.

Now, of course, that means lithium-polymer batteries won't have a problem since the highest legal cell count pack is 3 in series, or 11.1V. You can only safely charge that to 12.6V anyways.
The competitors should have shorted the battery until it was under 18 volts and then it would have been legal to use.
That's just dangerous and irresponsible. Somebody could hurt himself doing that, not to mention the chemical fire hazards of overheating batteries of certain chemistries.
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Re: Sumo Bots B/C [NY Trial]

Postby andrewwski » January 4th, 2010, 10:57 am

I suppose it could be - I've done it, but yeah, especially with too thin of a wire I suppose it could be dangerous. I'd probably discharge through a resistor.

There's always a way of draining a battery though. Even putting the battery in the bot and running it for awhile would do so - provided you could drain enough before impound is over.

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Re: Sumo Bots B/C [NY Trial]

Postby gh » January 4th, 2010, 8:13 pm

http://www.youtube.com/results?search_q ... um+polymer
http://www.youtube.com/watch?v=joe_TBzD49Y

Even ignoring the obvious risk of seriously injuring yourself or burning down your house (lithium battery-related house fires happen a lot), you really, really do not want burning metallic lithium chewing through the mondo surface in Gillis Field House. I imagine the Secret Service would come after you for trying to "terr'ise the West Point."

Also, a decent lithium charger should balance and discharge in addition to charging. The $50 charger I used could discharge with a current limit at up to 5W, I believe, and ran off of 10V to 16V, so I could actually discharge my battery without a power supply. Discharging the top 10% of my 13.2V, 2.3Ah battery pack would have taken 36 minutes at 5W, which should be enough time to make impound. Not that it matters, since, again, it's battery spec that counts, not charged voltage.
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Re: Sumo Bots B/C [NY Trial]

Postby Ubermensch » January 10th, 2010, 12:06 pm

In my experience, a concave "scoop" is best--assuming you can undercut your opponent's bot.


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