Newbie questions - main one - how cheap can a bot be? Advice please. :)

[hibernated]

Hey all!


I had a nice nostalgia hit last night watching a few old recordings of Robot Wars and now I need (yeah, need) to convince some of my friends it's a good idea for us to do our own little robot wars... thing...


Plan was I'd get the basic components and let people put them together and build the chassis, weapons, etc. out of whatever they like. Until I actually started researching this I thought it to be a great idea...


I still do, really.


But I'm already stuck-ish. So far I've determined that for each robot I'll need to get:
- 3 servos (2 wheels, 1 moving weapon)
- a transmitter/receiver pair with 3 channels (channel per servo)
- maybe some gears so people can fiddle with speed vs power
I've got wire and wire strippers so nobody needs to get that, and they can all provide their own batteries, sticky tape, pringle lid wheels, scalpel blade axes, etc.


Everything I research though just raises more questions... for now, just the main one...


1) I figured since you can buy a remote control car for well under a tenner I'd be able to get all the electronic parts for each robot for £5-£10. How painfully wrong is this? >.<


Don't crush my dreams too hard.
Cheers,
h

edit: off to work now but will have some less boring questions later- promise! >,<

[Niels - Team K.a.L.M.]

First off, welcome.

Those cheap rc toys often use 27mhz or 40mhz. These systems come with a prefixed channel and might be the same. Transmitter A could very well be controlling receiver A and C that way.

Servo's can be picked up for under 4 pound a piece.

Why don't you try to convince them to build a true featherweight as a team.
This can be done for less than 200 pounds total.

[hibernated]

Hi Niels - thanks for the welcome and reply.

What you wrote about prefixed channels actually answers one of those 'more interesting' questions I said I had - "will I need a different model of receiver/transmitter for each person or can the channels be switched?". I'm guessing then that only more expensive models can have the frequency changed? I was hoping maybe it could be altered some way... Still maybe if the cheaper models are fairly standard I can get away with just buying receivers and using controllers from old toys I'm sure will be stowed away somewhere... I'll have to look into it.

Can I ask what you think the minimum total price for a robot can be? (though I see you're in Holland, so I guess the market will be a little different) This is bearing in mind that chassis and weapons, anything non-electronic really, will be made from stuff around the house and competition will be light hearted at most - the parts don't have to be high quality as long as they work.

As for building a quality robot all together... Do you mean to enter a proper event, rather than doing our own?

That is an awesome idea! I hadn't actually considered it myself as, to be honest, I was unaware there even was a fighting robots scene until I came here. It would be easier to convince everyone to do our own, less serious, competition first I think (depending on cost) but if that went well I could certainly throw the idea out there!

Course... you'll be seeing many more silly questions if we do end up building a proper bot.

[psychostorm]

Hibernated,

Try the antweight category (150g, 10cm cube). They've used the likes of servos and card in the past and is more like a weaponised sumo than the larger weight categories.


Most of the antweight stuff largely hides around http://robotwars101.org/forum/

[Niels - Team K.a.L.M.]

I suppose for your idea, a private among friends event, a beetleweight might be an option.
Those cost roughly :
12 pounds or so for a pair of gearmotors.
18 pounds for a pair of 10a botbitz speedcontrollers.
10 pounds or less for a small batterypack.

And to keep it safe a 2.4ghz transmitter/receiver.
Costs about 40 pounds or less.

Check out some of the beetleweight buildthreads on here.

Biggest plus is that the parts are cheap and less fidly than servo's.

[Eventorizon]

Just a note, modern digital transmitters don't have a frequency as such, they operate on 2.4GHz but are bound so that they cant control the wrong receiver (That's the very simple version) Also, toy cars are mass manufactured bring the cost per unit down much further than we can ever achieve in a one off machine/robot.

I don't build Ants but I know they can be VERY cheap (Like under £50 easily), next its beetles where you could get one done well for £100 and then feathers where it has been done for less than £100 but ideally at least £200, excluding the transmitter.

That said, my first featherweight was £600 and was very ambitious for a first time build so you can leap out the blocks provided you have the right knowledge.

Good luck

[hibernated]

Thanks for all the input everyone, sadly it sounds like it'll be too expensive for me if I'm getting multiple bots built and planning to cover most of the costs... £40 just for the transmitter, £100s (or £600 ) for a bot... I'll be subsidising at least 6 robots >,<

I have been poking around the various weight class forums on here and figured ant weight is probably cheapest, though I can obviously make up the rules to fit the parts we have available. I'll check out the link too though, cheers Psychostorm

It sounds like transmitter/receivers are the most expensive parts... maybe I can find a way around that cost... and speed controllers are needed it sounds like? There aren't parts that just take input straight from the receiver? Makes it tricky cost-wise...

I found these servos on Amazon pretty cheap, but it says 0.12seconds/60degrees in the speed section, does that mean they only turn that far or is the rotational speed given in radians or something (1rad =~60*)? http://www.amazon.co.uk/VicTsing-Mic...productDetails

Thanks again for all the help - I'll keep working on it...
h

[Rapidrory]

You can get those servos even cheaper here: http://www.aliexpress.com/item/Tower...995280250.html
I bought a load a while back and they work just fine.

If you can hack them to continuous rotation then you can get a full drive system for £2 a robot, albeit a bit slow. Would then just need battery, transmitter and receiver assuming you made the wheels yourself.

Cheap2.4GHz transmitters: http://www.ebay.co.uk/itm/Blade-Heli...item35c2d32ee2

Cheap2.4GHz Recievers: http://www.lemon-rx.com/shop/index.p...&product_id=92

Cheap antweight motors: http://www.aliexpress.com/item/N20-D...255308477.html

Cheap wheels for the motors: http://www.aliexpress.com/item/Whole...864343611.html

I build competitive antweights for about £16-£20 each (as such I have ~15 of them now), but I only have one or two transmitter for the lot, and I make all the electronics myself. If you used the hacked servo boards to drive the gear motors then you'd get about the same price per bot, and if you just used the hacked servos, you'd get even lower.

[hibernated]

Well that sounds a lot more like it! I'll check all that out - cheers, Rapidrory.

Have you hacked those servos for continuous spin yourself? How difficult is it?

I'm currently looking into the possibility of building rudimentary transmitters, receivers, amplifiers and motors myself. Since the weight limit is whatever I choose and we'll all be using more or less the same parts there's little reason not to if it works out cheaper. Other than time of course, which is a concern...

All the better though if I can avoid all those miles from China I suppose.

[Rapidrory]

You can't do your own transmitters unless they're infra red for legal reasons, as you need to get it certified and it all gets very tricky. You can however buy transmitter modules fairly cheaply which are pre certified and you just need to attach a micro controller and joysticks to. Either that, or if you don't stick with DSM2, I have in the past found cheaper transmitters and receivers, but i couldn't find the link again..

I've hacked the servo boards in them before for Nanoweights; just switch the potentiometer out for a pair of ~2.2k resistors. Converting the rest of it should be fairly straight forward; remove the potentiometer from the casing and cut out the little bit of plastic that stops it rotating the whole way round.

Motors are not worth building yourself; the one's I linked are very good, and at £2 each they're not going to get much cheaper without going to Nanoweight components.

And if you're going cheap then China is your friend; very low prices, and nearly always free postage. Takes 2 weeks but that's usually ok. I buy nearly all my parts direct from china.

[gizz]

I agree to rapidrory on the motors and about the transmitter. Sometimes u can find deals where u get 2-3 servos with the transmitter / reciever combo and they might be hackable aswell.
Motors are more reliable than modifying the servos and at that cost its a great deal.
I've started ordering more and more stuff from china as most top rated sellers have free postage, it usually takes 4-7 days but can take 2-3 weeks if unlucky.

[hibernated]

Mm, ok. I'll have to look into the modules then. Though I think homemade transmitters are legal if you stick to the regulations - found something I think is relevant here (not sure, mind), under exemptions - http://stakeholders.ofcom.org.uk/enf...nforcement/law

Are motors easier/cheaper to use than servos? I thought servos were meant to be easier, but from what I've read so far they're actually a bit more complicated? Especially as they may need modifying just to work!