Sumo Bots C

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Sumo Bots C

Postby Jim_R » July 9th, 2010, 6:30 pm

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Re: Sumo Bots C

Postby paleonaps » August 17th, 2010, 5:35 am

Didn't Sumo get axed, according to the rule book? The Table of Contents doesn't have it.
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Re: Sumo Bots C

Postby AlphaTauri » August 17th, 2010, 5:51 am

Naps...that's last year's Table of Contents. None of the new events are in there, and the bolded ones are last year's new events.
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Re: Sumo Bots C

Postby paleonaps » August 17th, 2010, 8:13 am

No..... really?
Wow.
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Re: Sumo Bots C

Postby zyzzyva980 » August 17th, 2010, 11:33 am

This is one of the more anticipated events, I doubt they'd axe it, especially if they want to get interest up.
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Re: Sumo Bots C

Postby paleonaps » August 17th, 2010, 8:26 pm

I hope the bot can be bigger than 2000 grams. That's really small.
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Re: Sumo Bots C

Postby ichaelm » August 21st, 2010, 10:18 pm

Nice, glad to see this up :)

I just wanted to say that in the past month or so, between summer school and vacation, I've been part-time working on the art of etching PBCs! I divided the sumo bot circuitry into two parts: first the logic board, which interprets the signal from the radio receiver and sends signals to the next part, the power board, which is basically a motor controller. Surprisingly, my power board worked perfectly with the medium-power motors I have. It was basically two H-bridges using P and N MOSFETS, with some simple circuitry with a NOR gate chip so that I could theoretically control four states: forward, backward, shorted, and disconnected, with only two parallel signals from the logic board for each motor. It was also pretty small. The logic board, however, was pretty much a failure, mostly because I tried to do it completely in analog. It was impossible to make it precise and consistent. Next time, I'll try a more accurate digital design.

The actual etching-a-PCB part was a pretty cool experience for me. You start out with a flat piece of plastic, fiberglass, or whatever, that's coated on one or both sides with copper. Then you have some sort of etchant, which dissolves the copper on contact, and another "etch-resist" chemical, which you can apply to your board in the exact pattern you need to make the traces and pads. I don't have any of the fancy equipment that I really wish I had the money for. The only things I actually bought were the etchant, which was some ferric chloride from Radio Shack, and drill bits. The internet says that you can get great results by printing your design with a laser printer on glossy paper, and then ironing it on, but I couldn't get that to work for me. I experimented with a lot of different resists, and the best one I found was nail polish! I was able to apply it with a normal sewing needle in very fine patterns, and then either wait for it to dry or pop it in the toaster if I was impatient. The etchant needs to be hot to work, but ferric chloride makes some nasty fumes when it gets hot, so I set up two fans blowing out the windows of my kitchen while I used the microwave. Then I left it in a glass bowl outside. It took a lot of trial and error, but once I perfected the nail polish it worked consistently. Then you need to drill the holes, assuming you're using through-hole components. Some components, especially in the DIP package, require REALLY thin drill bits. I got some that were gauge 70 or so, or around 1/32 inch, and some others gauge 65 and 60 for bigger things like the power transistors. Then, I had to practice soldering again XD. That wasn't that bad though. In all I was able to make a pretty good quality through-hole PCB in around 6 hours.

This is definitely not something you need to do to build a sumo bot. I obviously went a bit overboard with the do-it-yourself attitude, partially to save money and partially because I thought it would be fun. And it was! But you can easily have some factory make a PCB for you for somewhere around 100$, I think. Or you can buy pre-made things like motor controllers and programmable microcontrollers like the basic stamp, and just program it and hook them up to each other. Or you can use a proprietary full system like vex. And the simplest option would be to buy a RC car and just add a shovel or something XD It all depends on how much time, effort, and money you want to put into it.

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Re: Sumo Bots C

Postby bridgebuilder25 » August 22nd, 2010, 8:21 pm

Does anyone know approximately how much torque a 2 kg bot can take until it becomes overkill? In other words, when will the wheels start to slip?
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Re: Sumo Bots C

Postby Ubermensch » August 23rd, 2010, 11:58 am

So has anyone implemented a braking device in their 'bot? You know, maybe a rubber-coated arm that can be lowered in the back of the 'bot to create traction and prevent it from being moved. I know this sounds like a "cheap" strategy, but I was thinking that an extremely light 'bot with a powerful and effective braking system could be used to "stall" out the opponents. It wouldn't be cheating per se, as the lighter 'bot will always win if there is no outcome after a certain amount of time.

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Re: Sumo Bots C

Postby ichaelm » August 23rd, 2010, 12:13 pm

I've built an electronic braking system that shorts the motor terminals, which is pretty different than what you want to do. My device definitely works, but I can't really tell how well it works yet, because I have yet to put it in a functioning heavy robot. I think your idea is definitely viable, especially if they increase the weight limit this year. But if your robot is already light, you might not need that kind of physical braking, unless you're using bad motors. My guess is that a lighter robot could make good use of electronic braking, but I don't have any test results to back that up. I may try that idea later, and if I do I'll post my results here.


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