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Dragon (beetle) - Team Savage


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Dreakoth



Joined: 20 Jul 2007
Posts: 46


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Dragon (beetle) - Team Savage

Class: Beetel
Chassis: Polycarb and Ali strut
Armour: Ali ~ 5mm+
Weapon: Ali fbs disc shell
Weapon control: Z-power 450 size brushless outrunner powered by random esc
Drivetrain: 2x COPAL 30:1 gearmotors running 35mm foamlites
Drive controller: sabertooth 2x5
Batteries: 3s 11.1v lipo ~900mah maybe go for 4s for fun.


Hey guys, dunno if this is the right forum but meh this is the only part of the forum i visit Razz

I'v got some ideas for building a new bot, basically i have a new hobby lathe and i want to make use of it for my bot.


Basically looking to do both a beatleweight and a feather, want to do a fullbody spinner or something in beetleweight to make use of my new lathe and redo my pnuematic axe bot in the feather.

With the feather the basic idea is to make my own custom pnuematic ram to get the size and weight down and stuff to make a more viable bot. I would try to make a ram / piston valve combo, and try to spec it to handle fullpressure co2 thats the end goal anyway, then build up a feather with drill motors for drive, a sabertooth25 and lipos (as iv alrdy got this stuff)


I'm looking for two things, help on design and ideas on how to build a pnuematic ram, and ideas for things to build / projects to do on my lathe to get practise and skills up.


One question i have with pnuamtic rams ect, if i was to recess an Oring into an end cap of ram to make a seal on the push rod, does anyone know any info on how much you over size the oring, like would u have a 2.5mm recess and a 5mm thick oring? so u have 2.5mm of extra rubber for compression? basically looking for specs on how to set an oring properly to make a seal - and a relationship for the recess size and oring size to the pressure it could take. Also how much differnece between the rod and the hole in the end cap..

At the moment i would have to just trial and error untill something worked but that seems like alot of testing. And theres not alot of info on the net that i could find.

Cheers, hopefully i can pick ur brains and end up with something good.


Last edited by Dreakoth on Sun Jun 06, 2010 7:10 am; edited 1 time in total

Post Tue Jun 01, 2010 4:54 am 
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Philip
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Joined: 18 Jun 2004
Posts: 3842
Location: Queensland near Brisbane


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Full pressure CO2 is fun. Trent, Assassin, has built a brilliant FP ram. He will be able to help you. Woody has made a very helpful site http://www.teamonslaught.fsnet.co.uk/pneumatics.htm

My advice is to start at the end result and work backwards. How much force do you want out of your weapon? Double that force to allow for friction loss. That will tell you how big your ram will need to be. Triple your ram volume and that is your buffer size. Woody's calculator will tell you your required Cv. Choose your valve to suit. Work out the number of activations you will have in three minutes and that will give you the amount of CO2 you need to carry. My main advice is to build what you want. Have fun.
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Post Tue Jun 01, 2010 6:05 am 
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assassin



Joined: 27 Jun 2004
Posts: 1105
Location: SunshineCoast


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Building a FP ram @ the cutting edge of performance requires a lot of knowledge, so start reading and talking to people who have experience.

Check out Woody's website as Phillp suggested.

Heres some o-ring info:

http://www.allorings.com/gland_metric.htm

Also I don't wanna scare you off but pneumatics can be very dangerous, I would hope you are a mature experienced builder.
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Post Tue Jun 01, 2010 7:34 am 
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Dreakoth



Joined: 20 Jul 2007
Posts: 46


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Good info there, it would be nice and simple to do fp with a burket valve it seems - are they avaliable locally?

Doinging an internal piston / shuttle type valve - is the increas in flowrate worth the extra complexity? i think it would be less noticable in an axe where u have more time to swing it vs a flipper where once they leave the arm thats it. (still want it to swing explosivly)

Building a custom ram, could i use extruded ali pipe for the body of a fp ram? my civil eng friend did some calcs and depending on specs thinks it would be fine - and thoughts? or do i have to use like hydraulic pipe stock.

umm.. building a little spinner beetle weight - in design phase - whats the smallest timing belts you can get? beetle weight sized or are belts only going to be orings at this level?

also what mah are ppl running in beetle weights with a spinner / brushless weapon + drives. I'm thinking like 800 - 1000 mah?

Going to roll this into my beetle weight thread soon when i get design done and stuff, want some feedback as i havnt done much work with these types of things and im sure ill miss a bit in the design. But yeah nice build log and pictures to come im sure.

Post Sun Jun 06, 2010 6:17 am 
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Philip
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Joined: 18 Jun 2004
Posts: 3842
Location: Queensland near Brisbane


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Burkert valves are available locally. http://www.burkert.com.au/933.html The 5404 is the one many people use http://www.burkert.com.au/ENA/Products/Solenoid-valves/High-pressure-up-to-250-bar/5404.html If your engineer says aluminium pipe will work, then its good enough for me.
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Post Sun Jun 06, 2010 7:24 am 
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Nick
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Joined: 16 Jun 2004
Posts: 11802
Location: Sydney, NSW


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Fingertech stock some really tiny belts an Robot marketplace has the smallest standard sizes. I found the problem is getting short lengths, not small width.

Making a beetle FBS will be a challenge; what material are you planning to make the shell from?

Post Sun Jun 06, 2010 10:47 am 
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dyrodium
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Joined: 24 Aug 2004
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Location: Sydney


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Perfect a friction wheel setup and run the shell from the motor at 90degrees, cheaper and more compact, plus allows the shell to slip which might save the motor.
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Post Sun Jun 06, 2010 12:51 pm 
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Nick
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Joined: 16 Jun 2004
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Location: Sydney, NSW


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That would definitely be better than a belt, it could use a really small & high Kv in-runner motor. Getting the shell into the weight limit and still strong sounds like the greatest challenge to me.

What drive motors would work best? B16 motors would be pushing the weight limit and those tiny Fingertech ones are too fragile IMHO.

Post Sun Jun 06, 2010 3:45 pm 
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Jaemus
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Joined: 01 Apr 2009
Posts: 2674
Location: NSW


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quote:
Originally posted by Dreakoth:

also what mah are ppl running in beetle weights with a spinner / brushless weapon + drives. I'm thinking like 800 - 1000 mah?


I used a 910mAh and later a 750mAh in carbine, and it never discharged much that i could tell (although i dont have a fancy charger that tells me.) Both were 3S
I think with a brushless spinner youd probly be safe from > 500mAh

Other guys seemed to use batteries in the range you have stated, so i think you're on track there

Post Sun Jun 06, 2010 5:11 pm 
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Dreakoth



Joined: 20 Jul 2007
Posts: 46


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The brushless i have is this one i think - http://helifreak.com/showthread.php?t=20028 (scroll down) and the link there is the new one which is red(3800kv) so i think mines the old blue one(3300kv) - whats the diff with in and out runner? think i got an outrunner.

Im thinking of using a mag clutch thingy like glen, mainly cus i want to play with the idea and stuff (i like magnets) so hopeing that will save the motor.

Currently the shell is going to be Ali - once i have the insides and mag drive bit layed out i can see how much weight i have to play with. once i finalise the design more ill let u know how much weight i got to play with.

The drive motors are what i have on hand, im currently running them on thosse foam wheels which are prolly way to soft to carry 1kg so i might have to source something else - if i mount the motors so they cant take shock loads from hitting the ground should they have any issues? - i could probably try a design like carbine where its not direct drive.. and that belt idea is nice and light. (also gives me more little pullies to make on my lathe Very Happy)

So atm i have a 5mm ali shell i could probably take it up to 8-10mm - how do u guys think that will hold up? otherwise id have to go sub 5mm steel like 2mm mebe i have to crunch the numbers..

anyone know where i can source some 5mm thick 160mm diam magnesium pipe? Razz

Post Mon Jun 07, 2010 2:02 am 
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Nick
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Joined: 16 Jun 2004
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Location: Sydney, NSW


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That motor looks really good, probably a bit over powered & heavy though. The main problem I can see is the high Kv rating; its going to be spinning at around 33,000 rpm on a 3S battery pack, which is going to be hard to couple to the shell. You will probably need a 10:1 gear down, which means driving the shell near its edge with a friction wheel, like Angus suggested.

I am not sure how a magnetic clutch would work is a FBS design - getting it to work like a friction wheel will probably be very inefficient and doing a centre drive would need some tricky hub design that would be heavy.

A 5mm aluminium shell might be OK for now, but once other builders get their act together, its going to get badly dented!

Post Mon Jun 07, 2010 7:10 am 
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Dreakoth



Joined: 20 Jul 2007
Posts: 46


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Well im in WA so im prolyl not going to head over anytime soon untill i finish a new feather.

Motor is only 57g so i cant see it being too heavy - so ur saying 3krpm is all u want? why not 5k?

Um ill see how i can get a center hub setup but i cant see how it adds much weight, u alrdy need a shaft mounted in the center unless im missing something? (i dont think it would add that much weight depending on how heavy the bearings will be)

basic idea is to have magnets in the reduction pully (big side) belts driving that off the motor - the main pully / mag coupling sits on the central shaft with the shell, i was thinking dead shaft, live mag pully with a thrust bearing counter sunk with a tiny bit sticking out but seating inside the circle of magnets then the shell sits on the thrustbearing.

(pics to come soon Razz)

Do i need to run like rollers 3 or 4 for the shell to hit so horizontal force isnt taken up only by the main shaft? i figure its how u do it but is it a definate ? also do u need live rolllers or will a base plate be ok for it to hit up against?

TBH im still new to all the concepts involved in a FSB so im picking up the standard issues as i go along.

Post Mon Jun 07, 2010 7:50 am 
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dyrodium
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Joined: 24 Aug 2004
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Location: Sydney


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You would probably be ok with some slippery material like uhmw plastic for bumpers, but keep in mind if the shell does bend they'll jam it quick smart. For beetles it seems your rpm can be way more insane than any larger class, i'd aim for 5K minimum, i know some american beetleweights are geared way up to 10K and beyond and they all hit hard. You'll probably be wasting your time trying to find magnesium tube like that, especialy in australia... Shocked
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Post Mon Jun 07, 2010 8:57 am 
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