Sumo Bots C

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Re: Sumo Bots C

Postby Flavorflav » September 12th, 2010, 4:33 pm

I don't know if this is relevant, but i have seen a number of drivers get excited and start pointing their antenna directly at the bot, weakening the signal and causing the robot to react spasmodically. This can look a lot like interference.

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Re: Sumo Bots C

Postby JBoyd-NY » September 12th, 2010, 4:45 pm

Primate:

I'm not referring to the battery in the robot or the battery that powers the transmitter - the receiver actually has a small battery that powers it. Get the specs for your transmitter/receiver pair (schematics would be even better) and look for a battery in the receiver itself.

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Re: Sumo Bots C

Postby Primate » September 12th, 2010, 8:38 pm

Primate:

I'm not referring to the battery in the robot or the battery that powers the transmitter - the receiver actually has a small battery that powers it. Get the specs for your transmitter/receiver pair (schematics would be even better) and look for a battery in the receiver itself.
Ah. Thanks for clarifying. I have a really good feeling about this now--we had no interference problems two years ago with the bot, and I doubt anyone's looked at that battery since it was built. If that's the issue, you'll forever be my hero.
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Re: Sumo Bots C

Postby paleonaps » September 13th, 2010, 5:06 pm

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Re: Sumo Bots C

Postby M-E-T-H-O-D MAN » September 15th, 2010, 2:41 pm

I wonder how difficult it is to build one of these...
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Re: Sumo Bots C

Postby Primate » September 15th, 2010, 6:47 pm

I wonder how difficult it is to build one of these...
Building one is easy. Now building a good one, that's where it gets tough.

Go to your local hobby shop, and tell them what you want to do. You'll probably want to go with a 2.4GHz system, which means you can get a radio intended for helicopters and use it for your bot instead. (I find that it's much easier to control a sumo bot with two sticks rather than a pistol grip system.) Get some servos, motors, and wheels, and then come up with a killer design. Simple.
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Re: Sumo Bots C

Postby old » September 16th, 2010, 4:45 pm

Did anyone else have trouble using 2.4 at states last year? We had some serious interference against Vex bots. Kind of a shame... we had the lamest Vexer take out our custom built bot last year.
It is hard to imagine what would cause interference with a Spektrum DX5 system. That system is both spread spectrum and frequency hopping so it is very very hard to jam it. I have read some tests done on the two competing 2.4GHZ RC spread spectrum systems DSM2 (used by Spektrum and JR) and FASST (used by Futaba). Both of them tested as being virtually unjamable. In the test I found that even with a very strong 2.4ghz source very close to the receiver neither the DSM2 or FASST system lost control. In the same test several other inexpensive 2.4GHZ systems that did not incorporate frequency hopping did have serious problems with strong interference. It is important to understand that unlike much lower frequency RC systems, 2.4ghz systems have very short wavelengths (on the order of centimeters) and can be blocked by even small pieces of metal that might not block a much longer wavelength signal. Many of the better 2.4ghz system come with either two antennas or even two receivers so that you can put the two antennas in different locations and at an angle to each other. By doing this you greatly decrease the possibility of having your signal blocked by one of your motors, wires, frame or gears or some other piece of metal. It is of course also possible that your opponent could block your signal with some part of his/her sumobot so you may want to place at least one of your antennas near the top of the bot to decrease the likelihood of being blocked.

You may also simply have a problem with your transmitter or receiver. The antenna wire could be broken and so is getting a very weak signal. The transmitter or receiver could have a power problem (batteries, wiring or connection. The power supply, filter circuitry, or even the RF section of the transmitter or receiver could be flaky. There are many many possibilities but interference from either another bot or even from WiFi, Bluetooth, microwave or some other 2.4ghz source is very unlikely. All in all I would suggest that a properly functioning spread spectrum frequency hopping 2.4 GHZ system like Spectrum or Futaba is by far the least likely to have problems with interference at an SO competition. Although it probably wouldn't hurt to ask the spectators and competitors to turn off Bluetooth devices. Though they are very weak and not supposed to transmit on a frequency band already being used by another 2.4ghz device it may be possible, if 200 people with bluetooth cellphones are all using them at once (linked ear pieces especially), to at least slow down communications from your DSM2 or FASST radio. And by the way, all new Spectrum radios use DSM2 so it is unlikely that switching to another model within Spektrum would do anything to help. Finally, FUTABA FASST radios are crazy expensive, several times as much as most Spektrum stuff.

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Charging batteries

Postby old » September 16th, 2010, 4:58 pm

Sorry for the double post but what are people planning to do about recharging their batteries at competition. The rules specifically state that no charging facilities will be provided by the supervisor, which I take to mean that no power will be available for chargers, so how do we recharge batteries? With many rounds of competition possible you could need a whole pile of impounded batteries to keep the bot going for the whole day of competition, so what do we do?

I also noticed that though the rules to specifically allow impounding spare batteries the rules also specifically allow no work on the bot once impounded before "their first bout". Does this mean that you can work on the bot after the first bout? Also the rules say that you must be ready to compete within 90 seconds of being called. Does this mean that you only have 90 seconds prior to each bout to replace/recharge batteries, or is this 90 seconds just for getting the bot onto the "ring" and turning on the necessary switches?

Sorry for all the questions but the last time I saw Sumo Bots was at Nationals about 4 years ago, and then it was only a trial event so the rules were a bit looser.

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Re: Sumo Bots C

Postby ichaelm » September 16th, 2010, 5:08 pm

I think that for some competitions, including nationals this year, they are going to have 5-6 preliminary rounds (one in each time slot), and then a final round afterward. So each team will compete for one hour, and the ones that make it to the finals will compete for additional hour. Obviously this isn't an actual hour of continuously running the robot, it will actually probably be a lot less. So what I would do is use one fresh set of batteries for the first hour, and if we make it to the next hour, we'd use our replacement batteries. But I don't know if this tournament design will apply to many regional and state competitions as well. We'll just have to wait and see.

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Re: Sumo Bots C

Postby paleonaps » September 16th, 2010, 5:40 pm

They've been doing that in NY for as long as I can remember.
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