Getting started, what do I need?

Hi all, Ive been an avid fighting robot fan since RW1, and when my son came along, he istantly loved it too. Ive always wanted to build up a bot (mainly for my son), but I havent got the skills or budget to go for a heavyweight, having seen what can be achieved with featherwights (we were at Debenham, sorry cant remember the bots name, but it was a vertical spinner that fired another bots spike off into the arena wall), I figure that might be within my capabilities. As a first bot I was thinking of going for a thick plywood base, and using the technobots WW motors for drive, but after that Im a bit stuck, what sort of speed controoler would I need to run the motors, what capacity battery would I need too? IS model car RC OK to use in a fighting robot or is it the wrong frquency (Im talking about 1:10 th scale buggy RC here)
Any advice, or links would be appreciated

Regards

Graham

http://www.stupoo2000.pwp.blueyonder.co.uk/featherweights/index.htmhttp://www.stupoo2000.pwp.blueyonder...ghts/index.htm

RC model cars in teh UK Run on 27mhz or 40mhz. If its 40mhz then yes its fine to use for Combat robots if not then it is not allowed.

I would strongly advise against plywood. It is simply not strong enough these days you would need something like 10mm polycarbonate to survive against spinners.

Drive. Those wipermotors to me would seem fine but you will need large wheels to get any sort of a decent speed with them. Another cheep option is drill motors.

Speed controlers. The 30amp electrolises sold by technobots seem fine. If you can get the ones with external relays as they are much better.

Batteries: That comes down to two things cheep and heavy or more expensive and light. If you want cheep you will need about a 5amp sla for to drive drills or ww motors. If you want to go slightly more expensive you can get 3amp Ni-mhs from technobots for around 40pounds and these will do nicely.

I hope this helps.

Regards
Ian

Dont be put off using a plywood base to start with, we,re still using one. Its cheap, easy to work as you go through the prototyping stages, its as flexible and resilient as most other materials IMHO. As long as you fit some reasonable protection around the edges and a thin skin of something more trendy/expensive over the outside its fine againest most weopons weve encountered.

Once youve got the design finalised then you can use more expensive materials, initial testing is far, far cheaper in ply than polycarb.

Dont forget the main advantage of ply is that if/when it gets trashed it makes far better firelighting kindling than either polycarb or titanium ;)

regards

Tim Jones

Greetings Graham,
Welcome to the FRA forum. The bot you refered to at Debenham was ours, Scorpion Jr.
If I may offer a little advice. First, before you pick up any tools, think carefully about what you can realisticly hope to produce given your abilities, the facilities and materials you have available.
If you have an intrest in building a spinner, be VERY careful, and be certain that what you propose to build is safe. It is not just a case of spinning a big mass, you need to understand the forces involved and be sure that what you are supporting that spinning mass on is strong enough. For example our disc only weighs very slightly under 2Kg but it is suported on a 20mm dia. solid stainless steel axel suported by heavy duty flange bearings mounted in a frame made of 6082 T6 grade aluminium. If you think that is a bit OTT for a feather, consider the energy required to cut that spike clean off PLF and launch it across the arena with enough force to damage the makrolon screen. In doing that, our machine was subject to an equal force, so you need something strong enough to absorb that kind of energy no just once but time and time again. If you get it wrong and your design comes appart in the arena the only thing that gets hurt is your pride. but if it comes apart in your garden shed when you are testing it....!!! Even an average featherweight spinner is more than capeable of inflicting a very serious or at worst a fatal injury.
Im not trying to put you off building a spinner but please think about what is involved. you may do far better by buliding a simple push bot first off, bring it to a couple of live events enter in a friendy whiteboard fight or two and see how you like it. But if a spinner is still the way you really want to go, remember that if there is ANYTHING that you are not sure of just come to the forum and ask the question, there is a vast amount of know-how out there in the roboteering comunity and we are always willing to share it.

Good luck and safe roboteering,
Geoff,
Team Scorpion.

Hi Graham,

Tho Im not in an objective position to say so, FeatherWeights.org is great :-)

Geoff has put it very well- you can never underestimate the forces involved with spinners, and you must engineer accordingly. A very ridget, low friction set up is equally as important as the wepon motor you have powering the thing.

As with all things, it a balance- bigger discs can store more energy but take longer to spin up, smaller/lighter discs contain less energy (at a given speed) but consequently take a shorter time to spin up. It is tempting to go for the big disc/lower spin up time option, but I would advise against it- any driver worth his salt whose drawn against a spinner knows the age old tactic is to get up close and stay on the spinner so it doesnt have the oppoertunity to spin up. Hand in hand with this goes the choice for the weapon motor. Its not entirely correct to say that a bigger motor means a more powerful spinner- the actual explanation involves a bit more physics:

A flywheel (a spinner) is a rotating mass storing energy. On impact it releases that energy into its opponent. The motor puts energy into it by spinning it up- its energy comes from the motor. Motor power is measured in Watts- and a watt is a joule per second. So the higher the power, the faster the motor can put energy into the disc. In essence, bigger motors mean faster spin up times. And, as mentioned, the faster you can spin up, the better your postion in the arena. Well aligned, true and ridgid set ups reduce friction and allow smoother operation- all important in getting the most from your disc. In short its not a question of putting the largest disc in that you can- its got to be a more well considered trade off between opposing factors!

If after all that youre still commited, congratulations, you are ready to build a robot! As geoff said, this forum is a great resource, and if you are at all in any doubt about anything, please come and ask us- well all be more than happy to answer your questions.

All the best,

Eddy
http://www.featherweights.org>

Hi mate,
I found it easiest to start off just making a nice working drive system, and forget the weapon for the moment that can be added later on.
I found trying to make a whole robot first gave me too many problems to dort out, whearas just a good driving robot at first let me do things step by step and so i could work out what went wrong and why withought getting muddled up and confused.
This is how i found it easiest, but its upto you at the end of the day, and whether you are already familiar with the workings of robots.

Good luck with it and keep intouch with how its getting on!
Grant

I agree with the idea of using drills for drive, and the drill mod kits (avaliable from featherweights.org) make them very easy to use. As for batteries i think 3Ah is a bit OTT for most fights, 2-2.4Ah race packs should be adequate for most designs. Plywood is an easy material to machine and remember you can always replace it with polycarb at a later date.

3Ah may be a little OTT for a single fight, but if you can afford the price and weight then go for it. It helps greatly at live events unless you have a few sets of batteries because after every battle with 2Ah your batteries will be dead, this was my downfall and now im currently running 3.3Ah Ni-Hms, put them back on charge after every fight and i can get through an event without the need to change them.
Drill motors will be better if you can, and yes plywood is good, take a look at Bernard, they just cover their Plywood in other materials.
Grant

I mean 3amp Ni-mh i agree 3amp ni-cd is ott but the 3amp Ni-mh are the lowest capacity that will take the kind of current draw we need.

Regards
Ian

You obviously havnt come across the new Sanyo 2600 Nimh that outperform RC2400 cells (traditionally the benchmark of sub-c performance). Wow.

Eh, what, I missed that one. 2.6Ah Nimh sounds good. Ill look into that when I get the chance. Do you know if they are lighter in weight too! After all we are still running 4.8Ah (2x 2.4Ah Sanyo Nicads) for the heavy drive and a little more battery power would allow us to change the gearing and have a faster bot.

A 12V stick pack of RC2400 from overlander weight 585g

A 12v pack of the 2600SCU cells in the same configuration from overlander weighs 610g.

Not that you probably would, but dony buy them in stick packs as they are covered in 2 layers of heat shrink (one round each stick and one around the pack as a whole) which gives very poor cooling potential, and the cells are normally attahced via spot welded tags which have a much much higher resistence than soldered joint. Spaced packs are much much better for your batts and they last a lot longer when spaced, even longer with a small fan, or looking at it another way, you can push them much more for the same amount of damage.. Please dont be tempted to stick the cells in cardboard tubes :-) You may as well heat them gently with a blow torch. :)

My Gp Ni-Hm 3.3A are coated in 2 layers of heat shtrink and they dont get warm, even with the over-volting of a 12v gold to 24v.
Are the RC2400 a different size to the 2600SCUs then, its getting me confused lol, please tell me if it was a stupid question to ask! hehe
I would expect the 2600SCUs to weigh more than the RC 2400s if they have 200 Ah more.
Im confused.
Grant

Yo Grant - im getting thos batteries. I spoke to your brother on MSN about those batteries. Nice packs they are, claim to be better than Sanyo Sub C Ni-Mh packs.

The RC2400 NiCad and 2600CU NiMh and GP3300 NiMH are the same size Sub C cells and weigh the same. There might be about 2 or 3g difference between each cell as it might have a bit more acid or whatever inside it.

Mr Stu

Yer they give out 5Ah more than standard sanyo Ni-Hm cells i beleive.

Oh hmm, okie wel thats kinda funny coz someone confused me there, so then the higher ampaere batts should be best to buy? am i correct in thinking and should weigh in at slightly more due to the extra stuff inside (im not an expert on what makes upo the weight lol)
Grant

Its all to do with the chemistry inside- more electrolyte layers inside and so on. The weight fluctuates a bit but by very little. You can pretty comfortably say that Sub-C cells all weigh pretty much the same, or at least the variations arnt too big.

Its the chemistry that makes the difference. Traditionally Ni-mhs have a larger capacity that Ni-cds, and they dont suffer from memory effect so much. However Nicads can be discharged faster (i.e. you can pull higher currents from them) than Ni-mh. Thats quite a black and white way of looking at it, and thanks to advances in technology we have got to the point that some Nimhs cells are beginiing to outperform similar Nicd cells in terms of discharge rate, thus pushing Nimh into the lead so to speak :-) A case in point are the recently launched 2600SCU nimh cells, which are said to outperform the RC2400 cells (nicd), as well as having the obvious advantage of higher capacity.

As for the Nimh not getting warm, it depends on what youre doing with them. If you start pulling more than about 45A they start to get pretty warm. This is the point where having them spaced pays dividends. General word of mouth rates them at 45A continuous, 60A for a short time. The RC2600 cells, by the same token, are said to be good for 60A continous and 100A for a short time. Its all just a question of looking at whats best for your application.

Have i got this right, do i only need about 2,6 Ah batteries in a FW?

Yes, if theyre Ni-Cd or Ni-Mh cells.

You can get away with even less. If its not a particularly current thirsty robot (which would suggest a simple drive and non-electric weapon, ed flipper) then small er batts will do. I know of Feather Flippers that have been running 1300 packs quite happily (although personally I wouldnt want to go beneath 1700)

OK that sounds nice, what AH would i aprox need if i go for SLA batteries?

Depending on your drive and weapins.
I would suggest NOT to go below 2.8amp. You may get away with 2.1amp depending on your drive and setup etc, but 2.8amp is the average and safest.

Mr Stu

How do you guys get away with using so little power in your machines? Scorpion Jr. with the new upgrades now needs at least 6Ah worth of NiMH just to see it through a 4 min. battle and even then its touch and go!:sad:

Ahh but, Sir Chairman, Sir (Congrats btw), most people dont have a kin nasty great disc, spinning at n rpm on the back, do they?

Bob.

Geof, TAN used 8Ah, and now 9Ah SLA, are you sure the electrics in Scorpion Jr are ok? No short cirquits anywere?

Thanks for all the replies, sorry Ive not acknowledged the responders before now, but were just in the proccess of selling our house, and its gone a bit mental, so Ive not been online for a bit. In reference to Geoffs comments re safety, how do you guys go about testing out your bots? Obviously drive testing isnt too major an issue with feathers, but what about weapons testing? I dont think Ill be going for a spinner myself (at least not yet), but your comments and advice are certainly encouraging, so once the move is out of the way, Ill be putting some effort into putting a chassis together. Thanks again for taking the time to reply

regards

Graham

Ill be perfectly honest, I go out from the garage and hide behind a sheet of poly and start smashing things up. We dont live on a built up street tho, so I have quite large area of drive that i can play on. The more standard solution is to boldly drive out and find a good flat, quiet parking lot or someother good flat space. As long as there arnt any people around, youre onto a winner.

Ok, I have been thinking of using 2 fanmotors from personal cars as drives and those Electrolise speedcontrollers and I am wondering on how much Ah you think a good SLA batteri that will need? Im not planning on using any weapons yet as it will be my second robot, I´ll build an Ant first when i get the R/C

The fan motors use a lot of juice and are quite heavy, plus i think theyre times slightly, which means theyre designed to spin faster in one direction that the other. This is less than ideal as im sure you can appreciate. I would be tempted to go for something like 4 drill motors 9one on each wheel) for a decent pushy rambot. SLAs? as large as you can fit in the design and weight. Bigger batts mean not only longer run times but faster acceleration and faster turns. So go for ones as large as you can get.

the only problem i found with SLAs, is that if you go very large, you may end up having to build your robot around your batteries! And then if you do ever upgrade you have this HUGE space of nothing, and i personaly hate thatm, i live likkle sweet compactor bots, lol.

Oh and by the way, how can you find out from any normal shop what discharge rate batteries have, because the shops by me know f**k all, they cant tell the difference between NiCads and Ni-Mhs lol

Grant

LOL! oh dear.

http://www.overlander.co.ukhttp://www.overlander.co.uk seem to be able to tell you nearly everything you need to know about battery packs. go to electric flying packs section and search the pages. Just find a pack which uses the same kind of cells that you have, and it will tell you.

But for instance, the GP3300mAh pack on overlander says 35amps + contin.
It is atually 45amps contin, but thats when the pack has been made up decent. Eg with DECENT battery bars and soldered wire - not spot soldered/welded - thats poo and limits the amount of current coming out of the packs.

Mr Stu

Ok i have been wondering about drillmotors too, have found some cheap 18V drillmotors that are quite appealing (maybe spellt wrong, im swedish ) but then i wonder, do i have to buy a speedcontroller? If im not wrong then there is a speedcontroller on a handdrill right from the start? And one more thing, should i go for like a ~3000mAh NiCd battery pack to a R/C transmitter or something?

Just so you know, a 3Ah Ni-Cd battery is larger than most other battery packs for radio controlled cars. So they weigh more and are more expensive.

Concerning the speed controllers in the drills:
http://www.fightingrobots.co.uk/discus/messages/25/1201.htmlhttp://www.fightingrobots.co.uk/disc...s/25/1201.html

Yes its to do with the sizes etc.
A 3Ah Ni-Cd Cell HAS to be a C size cell to get that much capacity into a NiCad cell.

Ni-Mh can be a Sub C cell size and still get 3Ah into it, but less discahrge current thou.

Again you have to mix and match the NiCd and Ni-Mh cells to your robots use. Some people can get away with 2200mAh Ni-Mh packs, some people can only JUST about cope with a 3Ah Nicd pack. Depends on many things.

Mr Stu

alpha runs a 3Ah 24v Botpack, and they still get very hot after use and i only have enough power for one fight (although can do two if im carefull). Where as G3 was running a pair of very old 7.2v 1.5ah Nicads (race packs) and he still had enough for two fights. It just shows you the difference between robots.

Yep there you go. Really is on what your robot is meant to do.

Mr Stu

OK i see. Im thinking of a ordinary pucher as it will be my first real robot (except for an ant) so im just glad to get it running :D ok NiMh sounds like a better choice then

pucher? u mean pusher? if so then use NiCads, NiMh wont supply the power for a decent pusher.

Alan... I think my robot proves you wrong :)
As long as you get decent cells (GP 3300mah being- I think- the best) then you can make pushers quite easily with ni-mh. But thats only the case if you use the right motors.

but in all fairness MM isnt as powerfull as alpha, and alpha has had a lot more fights then MM.