Author Topic: Do I stand a chance? (Read 3972 times)

frank26080115 · « **on:** October 15, 2007, 07:08:53 PM »

Here's my new drive train base for my first mini sumo robot
It uses a Tamiya twin gearbox on 203:1 ratio with Tamiya tank tracks using the 1.5" wheels

http://i156.photobucket.com/albums/t31/frank26080115/mini_sumo_bot/DSC02659.jpg
http://i156.photobucket.com/albums/t31/frank26080115/mini_sumo_bot/DSC026582.jpg

I had to cut down on the axle to make it fit within the 10cm limit, I have 1.5cm for a pushing plow with line sensors under it.
It only weighs about 125g right now, the battery pack weighs about 125g too
I will be using 2 photocells with leds and 2 comparators to detect lines only at the front two corners.
And 6 IR phototransistors (3 in front, 2 side, 1 back) to my MCU's ADC, with emitters which will be turned on and off, and the object detection is based on the percentage of IR increased while the IR emitters are on compared to the IR values when the emitters are off. While the emitters are off, if one sensor is significantly different from the others, it will decide that it is an opponent's IR emitter.

Is there anything I should be improving on?

Ro-Bot-X · « **Reply #1 on:** October 16, 2007, 09:33:37 AM »

Yes. Tracks are the weakest on sumo robots. In front of my Lego mini sumo robot, you don't have a chance.

frank26080115 · « **Reply #2 on:** October 16, 2007, 03:18:45 PM »

So having all the mass on one point is better than having it spread out over a wide surface? Is that why? Or are you talking from experience?

Wouldn't tracks be advantageous if the robot was slightly lifted?

What if I replaced it with 2 solid rubber wheels of the same diameter with plastic wheels on the back?
What if I replaced it with 4 solid rubber wheels with the front and back linked by a rubber band (not touching the ground)?

Will neoprene foam wheels work well? What about use my tank cog without the track with 2 o-rings on each wheel (not connected to the back)?

I'll keep going with the tracked design until everything else is done, then I'll make wheels and compare.

Is torque or inertia more important?

What are the advantages of a large diameter wheel vs a smaller diameter wheel? Why do I see large wheels on almost all sumo kits?

Steve Joblin · « **Reply #3 on:** October 16, 2007, 03:57:19 PM »

Interested to hear what other say, as I would have thought the same as Frank... I would logically assume that tracks are better because they have more contact area with the surface... I wonder why that is not the case.

paulstreats · « **Reply #4 on:** October 16, 2007, 05:31:56 PM »

erm.. i did think this also, the larger surface area the more friction.
also 203:1 is a large gear ratio, ive got one of these gear boxes also and they are very powerful, i would be impressed to see anything force it the wrong direction against the gearing (they have a LOT of resistance when the motors are turned off). which brings us back to the wheels. larger surface area more friction.

i would keep with the design personally, but get as close to the weight restrictions as possible

frank26080115 · « **Reply #5 on:** October 16, 2007, 09:32:20 PM »

Does anybody use scales or some method of actually measuring the capabilities of their robot?

sdk32285 · « **Reply #6 on:** October 16, 2007, 10:06:16 PM »

frank-
I started a new thread to answer your question about measuring the capabilities of a robot because I believe it is important, and is a good stand alone topic.

http://www.societyofrobots.com/robotforum/index.php?topic=2165.0

JonHylands · « **Reply #7 on:** October 17, 2007, 05:42:25 AM »

http://www.huv.com/miniSumo/seeker2

- can tilt back more than 45 degrees with both tires still fully gripping
- uses fast gearmotors
- molded urethane tires (very sticky)

With treads like that, you're not going to stand a chance against any sumo with urethane tires.

Check out: http://www.davehylands.com/jon/Seeker2Drone-01.avi
for an example.

The other robot (Drone) uses the same Tamiya twin-motor gearbox, although with large R/C tires.

http://www.huv.com/miniSumo/drone

- Jon

frank26080115 · « **Reply #8 on:** October 17, 2007, 11:21:34 PM »

Is there a place I can buy cheap thin sheets/stripes of urethane (paypal, no credit card) to glue onto my tank tracks?

JonHylands · « **Reply #9 on:** October 18, 2007, 05:27:11 AM »

Urethane is a two-part liquid you pour into a mold - see http://www.huv.com/miniSumo/seeker3 for an example of what my mold for that tire looks like.

I'm not aware of anyone who sells pieces of it. The only place I know of that even sells tires is Lynxmotion:

http://www.lynxmotion.com/Product.aspx?productID=371&CategoryID=39

- Jon

JonHylands · « **Reply #10 on:** October 18, 2007, 05:39:41 AM »

With respect to "Do I stand a chance", the real issue is two-fold:

- what do your opponents look like? If they don't have molded urethane tires, then you really don't need them

- you can still have fun and learn a lot with a robot that isn't perfect. You can spend more time on software and processing sensor input. Look into using finite state machines to control it (I have the source code for Seeker 2 available on my seeker2 page - it uses an FSM).

- Jon

Ro-Bot-X · « **Reply #11 on:** October 18, 2007, 10:41:56 AM »

Quote from: sdk32285 on October 16, 2007, 10:06:16 PM

frank-
I started a new thread to answer your question about measuring the capabilities of a robot because I believe it is important, and is a good stand alone topic.

http://www.societyofrobots.com/robotforum/index.php?topic=2165.0

Check out my sumo robots made from Lego in the above topic.

frank26080115 · « **Reply #12 on:** October 18, 2007, 07:25:12 PM »

That lego robot doesn't look like mini class though, but wow, lots of wheels.

Jon, are you coming to the november CNRG this year?

I'm looking into the urethane, might try some but time is running out.

JonHylands · « **Reply #13 on:** October 18, 2007, 07:34:20 PM »

Yeah, I'm currently planning on coming to the games. I'm probably not going to be entering any robots this year...

- Jon

frank26080115 · « **Reply #14 on:** October 18, 2007, 07:57:50 PM »

thanks a lot for the info on the urethane, it's pretty far from my house but the subway should take me right to it
i plan on applying some right over the tracks, or should i make a mold from the track first then put the urethane into it?

i also read some stuff on your Drone robot, what is this "RC car sticky stuff on the tires"?

JonHylands · « **Reply #15 on:** October 19, 2007, 05:27:41 AM »

You won't have any success putting it right on the tracks - it is very runny. The place I got it from is in Toronto, btw.

What you might want to do is use silicone - run a bead across each link.

If you really want to use urethane, you have to have a mold. For your first mini-sumo, I personally wouldn't worry too much about it - there are so many other things to deal with to make a competitive robot.

- Jon

frank26080115 · « **Reply #16 on:** October 19, 2007, 10:55:43 AM »

well what i really wanted to do was this.
make a shallow and long mold, pour the urethane in it, and suspend the tank track right on top of it.
after it dries, simply epoxy it to the tank tracks.

we want to send our university applications with a picture of us holding up a shiny trophy (or whatever they give us) lol

SomeSaba · « **Reply #17 on:** October 20, 2007, 10:37:33 PM »

Quote from: paulstreats on October 16, 2007, 05:31:56 PM

erm.. i did think this also, the larger surface area the more friction.
also 203:1 is a large gear ratio, ive got one of these gear boxes also and they are very powerful, i would be impressed to see anything force it the wrong direction against the gearing (they have a LOT of resistance when the motors are turned off). which brings us back to the wheels. larger surface area more friction.
i would keep with the design personally, but get as close to the weight restrictions as possible

Im afraid, im going to have to disagree with the bolded text. Surface area does not affect friction. friction = uN = umg. Mass, gravity and the coefficient of friction between the two materials affect friction.

If you drag mass block 2 x 2 x 1 accross a table, the 2 x 2 face of the block will have same friction as the 2 x 1.

i did a lab like that in my physics class lol <3

Pressure though is affected by area <3

if i am wrong plz correct me :O

paulstreats · « **Reply #18 on:** October 21, 2007, 03:02:04 AM »

You are completely correct about friction and surface area.

The greater the surface area, the less pressure per metre there is pushing down. so the even though the surface area is larger, it is still supporting the same amount of weight overall as a small surface, but less weight per square cm than a small surface.

The way to improve friction is to alter the coefficient of the material, or to increase the weight/pressure down.

Larger tyres are usually thought of as giving better grip, this is either completely wrong or due to softer/stickier tyres are usually made larger and wider because they structurally have to be. Or of course the tyres themsekves are heavier.

maverick monk · « **Reply #19 on:** November 10, 2007, 01:38:29 PM »

that gearbox is strong! i have the 203 ratio set up in my work in progress bot with the same tracks and it is nuts, it will actualy run into a wall, and crawl up it with a weighted load. no torque problem here!

the treds are nice, id make thin rectangular molds of urathane foam and epoxy them onto the lugs of the tracks. that should work well

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Author Topic: Do I stand a chance? (Read 3972 times)

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