Sumo Bots B/C [Trial]

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Re: Sumo Bots B/C [Trial]

Postby gh » July 15th, 2010, 7:16 pm

I don't understand why you'd ever build light. There's a maximum mass for a reason. I designed under the assumption that everyone else would build to at least the pushing force given µ = 1.0 and given maximum mass, and at least about 10 ft/s of maximum speed (yes, per second).

The only reason you wouldn't be able to reach that kind of performance is money or technical capabilities. Beyond that point (getting a bot with good driving performance), it's all about practicing and maneuvers. No amount of fancy weapon mechanisms or these "light & fast" robots you fantasize about (seen too many cartoons, maybe?) can beat a fast, robust machine driven well by an operator with a lot of hours practicing.

You'd be wise to contact your closest regional team so as to build and practice your robots together. You will both benefit a lot from such a setup.
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Re: Sumo Bots B/C [Trial]

Postby lllazar » July 15th, 2010, 7:52 pm

I don't understand why you'd ever build light. There's a maximum mass for a reason. I designed under the assumption that everyone else would build to at least the pushing force given µ = 1.0 and given maximum mass, and at least about 10 ft/s of maximum speed (yes, per second).

The only reason you wouldn't be able to reach that kind of performance is money or technical capabilities. Beyond that point (getting a bot with good driving performance), it's all about practicing and maneuvers. No amount of fancy weapon mechanisms or these "light & fast" robots you fantasize about (seen too many cartoons, maybe?) can beat a fast, robust machine driven well by an operator with a lot of hours practicing.

You'd be wise to contact your closest regional team so as to build and practice your robots together. You will both benefit a lot from such a setup.
This event is 60% bot, 40% driver...your gonna need someone with some mad joystick skills, just putting two kids with robotics knowledge won't get you anywhere...i noticed something at nats, this event can trip people up because it's so unlike all the other events. This event requires skills other than the ability to study harder than everyone else - heres an example of what i saw,

A lot of drivers weren't concentrated. I saw that they struggled to think on their feet, and if you can't figure out what to do quickly, a decent bot with an experienced driver will take advantage of an and every opportunity present to them.
2011 Season Events~

Fossils (Regionals ~1st) (State ~6th)
Towers (Regionals ~1st) (State ~3rd)
Helicopter (Regionals -3rd gahhh) (State ~5th)
Wind Power (Regionals ~1st) (State ~3rd TIERED!)

Hooray for getting everything i wanted?

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Re: Sumo Bots B/C [Trial]

Postby ichaelm » July 15th, 2010, 8:25 pm

I don't understand why you'd ever build light. There's a maximum mass for a reason. I designed under the assumption that everyone else would build to at least the pushing force given µ = 1.0 and given maximum mass, and at least about 10 ft/s of maximum speed (yes, per second).

The only reason you wouldn't be able to reach that kind of performance is money or technical capabilities. Beyond that point (getting a bot with good driving performance), it's all about practicing and maneuvers. No amount of fancy weapon mechanisms or these "light & fast" robots you fantasize about (seen too many cartoons, maybe?) can beat a fast, robust machine driven well by an operator with a lot of hours practicing.

You'd be wise to contact your closest regional team so as to build and practice your robots together. You will both benefit a lot from such a setup.
I tried to do some calculations to try to see if you could get a ~2 kg sumobot to accelerate from 0 to 3 meters per second within a ~3 meter distance, running with reasonable voltages and internal resistances. But I realized it completely depends on the motor and gearing system, and I don't have the time to spend figuring all the math out (I'm not that great at math). But I've already done some tests on motors that I have, and they just don't come close in terms of the combination of torque and maximum RPMs you would need. Of course, most of my motors come from printers or RC cars and stuff, so it's probably a terrible comparison. One idea I came up with was some sort of gearshift, to keep the motor running at its most effective torque and changing the gear ratios to compensate. But I really don't think that's what you had in mind. It's such a short distance that a gearshift would be practically useless (correct me if I'm wrong). If you have motors with that kind of combination of torque and maximum speed, please inform me where I can get some!! :P

Because it is definitely true that a 2 kg robot going 10 feet per second will dominate over a 1 kg robot of similar speed and design. The problem, as I see it, is matching high speed with maximum mass. I have not finished my first sumo bot yet, and you've built one or more already, so I figure you've figured this out already. Is it really just about getting the most powerful motor money can buy? (and matching it with an effective wedge or something). I hope not; up until now I've been building my robot completely out of salvaged parts from broken stuff we have lying around and basic electronic components (transistors, etc.). Except for that radio set, which I've temporarily borrowed from a really cool old handmade tug boat we have for no reason (we live nowhere near a lake or anything), and I promised to put it back in the boat as soon as I get a legal set. If I need to get 100$ motors or something it'll ruin my cheapness :roll: . BTW this is just for my first design over the summer. For the real one we're definitely going to use more specialized parts and digital electronics.

Sorry, back to my main point: Can you elaborate on what kinds of motors you used, or why you do/don't need super expensive motors?

PS I understand the value in practicing :D Especially with something as fast as this is supposed to be.

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Re: Sumo Bots B/C [Trial]

Postby gh » July 16th, 2010, 5:35 pm

I had 550-size motors, where the "-size" is a quasi-standard for a motor whose can is about 55mm long. They are easy to find, but finding a good gearhead or gearbox for them will be hard. That's why I think power tools are a much better source of powerful motors with gearboxes. Cordless drills will even have decent batteries to rip out. My initial blueprints for my senior year bot involved DeWalt cordless drill motors (roughly 1.2kg for a pair; you can imagine their size) and half of a DeWalt 36V LiFePO_4 pack, but that was too insane even for me.

What I used (see earlier in the thread) was far overkill even for my somewhat lofty goals. Remember that with powerful motors you need powerful motor controllers and batteries. My batteries could give about 1kW (2kW peak), though my first motor controller spazzed out at .25kW or so because of overcurrent protection. An accelerating bot consumes a metric heapin' of power, I'm afraid.

Also, for my current project in college, my buddy and I are making my own sensored brushless motors because the torque and peak power we need far exceed what our budget can provide.
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Re: Sumo Bots B/C [Trial]

Postby ichaelm » July 17th, 2010, 9:46 pm

A while ago I did some research on different kinds of batteries. If I get any motors more powerful than the ones I have access to now, I'm going to need less internal resistance. An average NiMH or NiCD cell has an internal resistance of around 0.06 ohms. This means that its maximum usable power is about 6 watts per cell, or 72 watts at 14.4 volts (12 cells). And I'm pretty sure those kinds of batteries aren't meant to carry over 5 amps. I guess the logical next step would be LiPO, which you talked about. SLA is just too heavy :lol: . I'm not sure if I'm ever going to need that kind of power though. Like you said, at some point you're limited by traction and other factors. With my motors. it would be fruitless to go over 50 watts. Although my motor controller is custom built (actually it's still in the breadboard) so if I really need to some day I can swap in some even bigger transistors. I think the only way you could actually benefit from over like 200 watts of power would be with sticky wheels, or treads (um no). And I hope they outlaw adhering to the floor; it can just get out of hand.

I was thinking: what do you guys think about brakes? Has anyone tried a physical braking system? Pretty sure you'd only ever need physical brakes if your motors were really weak (or not geared down enough). What about shorting the motor terminals? Is it effective/safe/necessary? Just trying to get some input from more people with more experience.

EDIT: see next post...
Last edited by ichaelm on July 24th, 2010, 10:37 am, edited 1 time in total.

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Re: Sumo Bots B/C [Trial]

Postby AlphaTauri » July 18th, 2010, 2:39 pm

Ichaelm, are you talking about a braking system (providing resistance to motion) or a breaking system (well, um, breaking things)? 'Cause there's a big difference.
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Re: Sumo Bots B/C [Trial]

Postby ichaelm » July 18th, 2010, 3:44 pm

hahahahahaha wow

the power of e...

yes I mean braking.

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Re: Sumo Bots B/C [Trial]

Postby paleonaps » July 19th, 2010, 6:34 am

There is a huge difference.
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Re: Sumo Bots B/C [Trial]

Postby lllazar » July 20th, 2010, 10:03 am

There is a huge difference.
Positively gargantuan....
2011 Season Events~

Fossils (Regionals ~1st) (State ~6th)
Towers (Regionals ~1st) (State ~3rd)
Helicopter (Regionals -3rd gahhh) (State ~5th)
Wind Power (Regionals ~1st) (State ~3rd TIERED!)

Hooray for getting everything i wanted?

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Re: Sumo Bots B/C [Trial]

Postby paleonaps » July 24th, 2010, 8:42 am

So with this being a national event next year, do you think they'll take better crowd control measures?
I don't know what happened at Nationals, but in my state it was a B event, and the crowd was pretty well controlled. The previous year, however, it was awful. The whole audience was right up against you, and....ughhh. It was so nerve racking. I think this year we were lucky to be in an area that didn't allow that.
So how was it at this year's nationals, and what do you think for next year?
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Farewell Science Olympiad. We will meet again.


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