University featherweight battle

[Yohooshi]

Hey everyone, I've recently been set the challenge to build a featherweight robot for a battle that will take place at the end of March. I would like to implement a flipper into my design if possible, I have read through lots of forums over the past few days trying to get an idea as to what some of the terminology means, what components I will need and where to buy it.

This will be my first time building a robot and I'm in a group with 6 other people who all have no experience either. Seeing as we are students we don't have much money to spend on equipment therefore the cheaper the better.

The materials provided by the university are: Steel/MDF for the body, 2 drills motors, 2 servos for speed control, controller and receiver.

The only things not funded are the wheels and weapons. I was planning on buying rubber wheels (nothing too special because I can't see any of the other robots doing much damage).

My question is what size ram would you recommend buying, it's doesn't have to be anything spectacular, just enough to flip a robot over or even slightly lift them off the ground.

Another question I have is if I were to buy a 12oz paintball co2 cylinder what size buffer should I buy and roughly how many uses would I get out of it.

Sorry for the essay I'm just very keen to get started, also sorry if these questions have been asked before! I'd appreciate any help or guidance any of you could give me.

Thanks

[maddox10]

Working pressure of the setup, and the wished for effect are 2 things I need to know before recommending a size.

Also, it's the size of the ram that dictates the size of the buffertank, and the amount of flips/lifts you can get from a 12 oz bottle.

[bitternboy]

How are you using the servos to perform speed control?
Also, what uni are you at? I was chatting to a new module leader at Sheffield who wants to do something similar; I can point him in your uni's direction :P
I'm aware I'm asking questions instead of giving answers, sorry

[Runsler]

Also, do the drill motors come with the gearbox? else you might have a problem there...

[Yohooshi]

Hey everyone thanks for the quick response.

@bitternboy

For the speed control we will use 2 servos, one for each motor. They will mounted on a copper circuit board and be able to go 2 different speeds, full speed and half speed. Half speed is achieved by connecting 2 resistors (one for each side of the board). <- That's a rubbish description but I'll post a picture when its been built.

I'm at Brighton University and the module is taught by Ian Watts if that's useful to you.

No worries about asking questions, ask as many as you want!

@Runsler

Yes the drills do already have a gear box all I need to do is lock the clutch (I think so anyway).
@maddox10

I will say we would operate it at about 8 Bar. Does lower pressure mean less gas used (meaning more flips) or is that not how it works? For the size of the Ram I just want a small system, nothing large and expensive. Sorry for all of the questions but I really don't understand pneumatics very well (electronics student).

@everyone

Thanks

[bitternboy]

For the speed control we will use 2 servos, one for each motor. They will mounted on a copper circuit board and be able to go 2 different speeds, full speed and half speed. Half speed is achieved by connecting 2 resistors (one for each side of the board). <- That's a rubbish description but I'll post a picture when its been built.

I'm at Brighton University and the module is taught by Ian Watts if that's useful to you.

Ah, gotcha, that sounds like a pretty fun build! Ad hoc micro-switch/servo speed control makes for quite a jerky driving style but you can probs get used to it.

Thanks for the tip off, I'll pass it on

[RobotExtreme]

Hi Yohooshi,

What you discribed is an Mechanical Speed Controller (MSC), many years ago used on RC models before what we now call ESC.

http://radiocontrol.wikia.com/wiki/M..._speed_control

I can´t not say that this type of application on a Fight robot is hazardous:

-For be very fragile during combats.
-Most important, if the mechanism "break/stop/stuck/battery disconect" at a "on" position you can´t control the robot moviment, what can result in accidents (I used this solution many years ago on weaponless Hobbyweight ). Same could happen with a ESC, but its a LOT harder to happen. Im not sure if anyone will not allow (even rules) you to compete with this system, its just an advise.

Guilherme

[lowndsy]

Was it Gemini back in the old days which used a servo to control the joystick of an electric wheelchair?

[Runsler]

As far as i understand, you'll only use the bot for "intern" combat, meaning just you and other students in the same module, right?
So i wouldn't care too much about safety rules or jerky drive style, since all competitors will have that (and it seems mandatory, so... no use in switching it vs. a somewhat expensive esc, and getting an unfair advantage, i think )

Only three considerations that could be done from that:
1. Mention that nowadays standart would be an esc, and the safety issue. could be your prof changes his mind due to that, making you use an ESC instead of MSC. But i think this solution was choosen mostly on budget questions or because they already lay somewhere in the university.

2. build a bot that doesn't need too fine driving. (So... a horizontal spinner for example), or choose wheel size (and therefore speed) rather a bit smaller (so slower) if aiming is more important than actual speed (for example in a vertical spinner).
Will drive a bit like steering any race games with a keyboard... many small tips on the keys to make wide curves.

3. With the MSC being rather fragile, a strong flip could be devasting. If you can aim right, and won't flip into nothing, with the recoil destroying your own bot



And for the pneumatic stuff... i never got into pneumatics, but:
"pressure" of a gas can be seen as how many gas atoms are in a given volume. (well, kinda.)
So if you have a given amount of atoms in the gas tank, and you operate a system with a higher pressure, you are very likely to blow out more atoms at once, making the tank last a shorter time.
But Pressure alone isn't the only thing to consider when trying to build something "powerful".
Pressure is just force per area (is my english right here?) -> p=F/A -> F=p*A
So you'd want a lot of force to flip the other bot. Building up a high pressure is one thing, but increasing the size of your system, mainly the area the pressure works against also increases the force you get out of it.

And since weight is always the biggest struggle:
someone actually used that for a bot should explain what size/weight ratio of all the parts needed is most efficient.

Also, as always, leverage is important. so how far from your hinge will your gas system apply its force, and how far from the hinge will the enemy bot be at maximum?

[maddox10]

Hi Yohooshi,

Lower working pressure means bigger rams to do the job you want to do with them. Bigger means heavier, even if the materials used can be build lighter in themselfs.

Advantage of 8 bar is that you can source commercial parts. Brands, Festo, SMC, Norgren, Metalworks or even "el cheapo chinese".

In the end , the gas in the bottle can be compared with electrons in a battery.
The more work you want to do in a certain time, the faster both will be discharged.

[harry hills]

Not a pneumatics guy at all but I'm fairly local, I'm an engineer down in Hove. Shoot us a line if there is any help I can be

[blazerbotics]

Personally I think it would be easier/cheaper to try running a compressor system, get a 32-40mm bore ram, a 12volt air compressor used for pumping up your car tyres, and a little 3/2 valve and find something to use as a buffer tank (old power fire extinguisher or metal sports water bottles work well). It won't be the most powerful setup but will give you enough to lift/flip robots over.

[Yohooshi]

Thank you everyone for replying so quickly!

@bitternboy

Hopefully the driving aspect won't be too difficult, no problem!

@RobotExtreme

Thank you very much for the advice, I do plan on doing future builds after this assignment but I the only thing is that for this assignment we get marked on our build quality so it is expected that we make our own MSC. With that in mind I'll ensure I take extra care when securing the MSC to the frame of the bot.

@lowndsy

I've just looked that up it could have been it says that it used wheelchair motors but I can't find anything about the speed control, but it probably was!

@Runsler

Yeah we'll only be using the robot against other bots made by students. I do know of one student that is using an ESC but he has been on robot wars and battle bots before so I think it's ok if he uses it. I would much prefer to use an ESC but I think that we do get marked on the build quality of our MSC, which is a shame.

We did consider making a vertical spinner because we thought it would be easier, that is done by just adding a separate motor and spinning the object, right? The only problem is that we aren't allowed sharp bladed spinners it would have to be a blunt spinner such as 'Carbide' in the most recent series but we didn't know what material to make the spinner out of as this has to be lighter than what is used on the heavyweight robots.

Thanks for the advice on the pneumatic side of things I'll get my group to do some calculations around that.

@maddox10

Ohhh ok, I get that explanation, thanks for the help

@harryhills

Will do, thank you for the offer

@blazerbotics

That could prove to be very useful and cheaper, I've just briefly looked it up and that sounds good. Thanks for the help

@everyone

Thank you all so much all of this advice is great

[Runsler]

With that in mind I'll ensure I take extra care when securing the MSC to the frame of the bot.

We did consider making a vertical spinner because we thought it would be easier, that is done by just adding a separate motor and spinning the object, right? The only problem is that we aren't allowed sharp bladed spinners it would have to be a blunt spinner such as 'Carbide' in the most recent series but we didn't know what material to make the spinner out of as this has to be lighter than what is used on the heavyweight robots.

1.When securing it, try to implement some kind of "buffer" between frame and MSC to absorb some of the shocks that are likely to happen.

2. "easier"... well it's a question of perspective. basically it is "just adding one more motor", but you also have to put an additional ESC (or MSC) into it to get power to it. Also, modern spinners use always almost brushless motors for that, and those just won't work with an MSC (as far as i know). You'd also have to balance the spinner, and have something to mount it that could take the forces involved. Actio = Reactio -> the same force you put into the other bot in a crash goes into your bot. on a vertical spinner maybe even more, since your bot is stuck against the ground, while the other would likely lift off and divide the energy between the crash on contact with the bot and the crash on contact with the floor. And well... mounting fast spinning things so they won't get damaged from shocks, don't heat up or anything else... one more thing to think about that might be new stuff to electronic guys So... all in all, principle of a spinner might be easier, but it has to be very well executed. Else your bot is likely to destroy itself, and something in it's surrounding, so testing that would be complicated and dangerous.

But not being allowed to use sharp spinners won't be a big problem here, since most spinners don't try to "cut" (would be kinda pointless vs. hardened steel and only split seconds of contact), but rather work with blunt force and try to deliver as much energy as possible in one hit, rather crushing/bending/ripping off/flipping/kicking than actual cutting. If the enemy uses MDF plates a cutting spinner is tempting, but anyway... most just use a bar, a disc or drum with one or more "teeth" (each quiet wide, so more for hitting than for cutting) or in that weight class a beater style weapon is quiet common, too.
And for the material: it doesn't have to be lighter, just smaller than a heavyweight.

Not wanting to spoil any plans, and personally i think a flipper is the cooler bot and can usually self-right without problem... Just since you were already thinking about it, i wanted to mention these things.


(oh, and don't give too much on my advice, i am really new to all this stuff and just building my first bot... a featherweight vertical spinner with a beater. Just because for what i have on equipment and knowledge the pneumatic stuff would be more complicated for me, and the gyroscopic effects of these bots look really interesting. Also, my driving skills just won't be good enough for a flipper, i'd never flip anybody but myself. So if anybody here corrects me: they are right.)

[Yohooshi]

@runsler

Thanks for all of the tips, we have decided to go ahead with the flipper and I'm about to buy the parts.

.

Can someone please inform me if these parts are compatible together and if I buy a 12V solenoid actuator would the set up work and does anyone know what valve I would need to buy.

https://www.bzpaintball.co.uk/12oz-c...with-pin-valve (Co2 tank)

http://www.ebay.co.uk/itm/NORGREN-PR...sAAOSwRQlXdSr4 (ram)

Thanks