Scioly.org

Luke Thomas wrote: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.

In their defense, people are often asked to run events they know nothing (or very little) about, putting them in a position where they have to make judgment calls with very little knowledge to base them on. In many cases they don't know they don't know! I have observed this most often in "building" events.

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.

andrewwski wrote: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.

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.

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.

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

this event sounds awesome, i wish my state hhad this trial event instead of the dumb ones they give my state...

sciencegeek100 wrote:this event sounds awesome, i wish my state hhad this trial event instead of the dumb ones they give my state...

It is awesome - or was, at least. Honestly, now that nearly everyone is using the same basic design (in C division at least), it is a little less awesome than it used to be.

My group and I need help right now. I'm a newbie in sumo bots and wanted to know how I could change the frequencies of a transmitter. Right now, I have a Futaba Magnum 3PM-FM T3PM digital proportional r/c system. Is it possible to change the crystals and if so, how?

Moreover, could anyone here explain everything I need to know for frequencies?

bchero wrote:My group and I need help right now. I'm a newbie in sumo bots and wanted to know how I could change the frequencies of a transmitter. Right now, I have a Futaba Magnum 3PM-FM T3PM digital proportional r/c system. Is it possible to change the crystals and if so, how?

Moreover, could anyone here explain everything I need to know for frequencies?

You need to get two more sets of crystals - exactly what you need depends on your receiver, too. You are probably best off bringing all of your stuff to a hobby store and telling them what you need.

This page from the NY supervisor covers frequency information very thoroughly:
http://newyorkscioly.org/SOPages/SumoFrequencies.html

Is Stuy using Harpy II or some variation of it at NYC Metro this year? I saw the computer prototype picture on geekshavefeelings.com, it looks like a big improvement over Harpy from last year's regionals, pretty sweet, and I'm kind of itching to fight it with my bot.