19th April 2017, 18:33
It's common advice but before you build anything read thru the build threads and get to a couple of live events so you can talk it all thru first. You will learn a load.
21st April 2017, 15:39
Feather spinners can be... well... i don't think there is any material left nowadays that is strong and light enough to take a good hit from one of the really good spinners and still don't take serious damage.
So it mostly depends on the angle. If your armor is 90° to the spinner, or even having some pointy bits standing out, you'll possibly get shredded. If i remember right, there were feather spinners ripping through 8mm armox. And as soon as you want an active weapon, even 3.2mm of that stuff all around might be too heavy.
So your best bet is to not give them 90° to bite into, but make it angled, so they will more "scrape" on the armor than to "bite" into it. You might even deflect a blow (mostly from the horizontal ones) so the spinner itself will get bounced and possibly having his energy backfiring at him.
Now the really hard thing is... how do you make it all angled from all sides, with the possibility to get flipped? But that's something you have to find a solution, or more likely, live with something "the best you could do".
Could also be a good idea to shock-mount the armor, but really depending on the kind of armor and all.
basically, any metal-based armor tries to deflect hits without actually absorbing any energy, and "tries" to stay as one, flat surface. Once it is bend or ripped, it will stay so and be a perfect weak spot for any hits coming after that or even locade your drive or such.
HDPE is more like "oh, you took a part out of me? so? try again, i've got some left". parts can be chipped out, but they won't be bend out leaving something for the enemy to "hook into", and won't be bend in and press against your drive or stuff like that. It will stay in shape, but get chunks get cut out of it. And that most likely with every hit, where some metals might just take a scratch, if even that.
What actually is better in a feather... depends on where and how it is used, and what you can work with.
With HDPE, you got two options:
Making the chassis from Ali or stuff like that, just enough to put all the electronics etc. together, and then put HDPE on that as the armor.
Or if you'd want to go with all HDPE, i think 20mm for the armor and 10mm for internal structures should be enough. Maybe even less for internal stuff, depends on what and where.
But: Never try to drill and tap into HDPE. The bolts just get ripped out.
For me, i do the screwing depending on if i likely need to screw/unscrew here often.
If the screws are mostly once in, never out again (like internal walls to base plate, or internal walls to other internals) just wood screws. And not just a few.
But can't do these for Top to Armor and stuff like that you'll likely want to open and close a few times (or in case of the armor: might have to swap for new parts to repair). After a few times of screwing and unscrewing you'll just have a big hole to look through, and any screw gets ripped out easily. So either take barrel nuts as mentioned above for these parts, or try to melt other, big nuts in sideways (didn't try that, but could work), or if the bot is flat enough, you could do what i do: drive-in nuts.
If it is box-shaped in any way and not too high, they work really nice. Just screw the box together with only a few wood screws (just to hold everything in place). Take a drill (ideally a drill press or a straight, steady hand) and drill 5mm holes through top plate, any walls, and bottom plate in one go. now make the holes 6mm on the first cm on one plate, and sink in the bolts from the other side. Now you can hammer in the nuts through the 6mm holes, or, what worked better for me: take one longer bolt and a washer from the other side, and just drive those nuts in. they get straighter that way, saving you trouble later on.
Take out the wood screws from the side where you sinked in the holes and not put the nuts in. I'd leave the few next to the nuts, just so not the hole chassis falls apart once you remove the bolts to open the top plate.
Might want to step it up a bit on the bolt size, i just used M5 because i had those around.
Downsides i found so far for that way:
-swapping side armor is not that easy without a drill press or having the parts pre-made. the holes have to be on the same place in the same direction.
-if the nuts don't go in straight, instead of bolting into them you could just push them out, and will have to try again. gets annoying.
- since sinked in bolts get flatter than the nuts, it could be wise to make the bottom plate removable, not the top, so you don't get stuck on the floor with these nuts. it's just 1mm or such, but could be enough. But gets a bit confusing with wiring the motors etc., and could leave you drive in the wrong direction when you turn the bot around again
In quiet some characteristics HDPE behaves like wood, so what's used to hold wood together or give wood the form you like, will likely also work for HDPE.
Anyway, it is definitely possible to make a working bot in a way you only need HDPE as material (maybe 10 and 20mm, if you have weight left more at least for side armor is better. if you stay with mostly rectangular and triangle shapes for the parts it is really easy to calculate the weight even without CAD or stuff like that. make an excel-sheet with all the surfaces of the parts added together in cm², once for the armor parts and once for internal stuff. now you can experiment and multiplicate those numbers with 0,5 to 3 or whatever. whatever you get from these numbers will be your weight in g. But don't forget screws, those are really heavy...)
Tools for this you'd only need some kind of saw (any saw will do, but some will better than others), a drill (preferably a drill press, too), maybe a few screwdrivers and stuff like that, something to put the electronics together. With some luck they're mostly plug and play, as well as some duct tape and zip tie, a knife and a hammer (you can always need those. The knife comes in handy, since you can even carve HDPE with it.) Possibly some hot glue.
You can even saw out round pieces of HDPE and screw bike tire in them as wheels.
So, with one spare sheet of HDPE in each thickness you use, you can make all the spares you might need (except for gearbox etc.) without too big machines to carry with you to an event. Big plus compared to guys who need a mill and wielding and whatever for their spare parts.
But, if you want to go anything wedge-like, you should consider make the top/bottom plate (partially) from some kind of metal. you'll just get a way sharper/sturdier edge with it. Hard to get under the enemy when you rammed the wall a few times with an edge from HDPE.
21st April 2017, 17:16
My original design had an elongated slanted edge around all sides of the machine which contained no electronics, just sacrificial HDPE and air behind it so there was room to be massively gashed by a spinner but still come off with theoretically no internal damage, and that's if the slanted angles didn't undo the spinners attack enough. this however may be too expensive (and large) with all the sacrificial HDPE that'd end up being... well sacrificed. Depends how often it came up against something devastating to HDPE. It does seem to be one of the cheaper materials though, and certainly one of the easiest/quickest to carve out replacements for.
Originally Posted by Runsler
I'm yet to decide what I want to do for weaponry. My original idea was to try adding a hunk of slanted HDPE to the front and get some powerful motors and try to make a simple ramming / pushing bot, however I don't think that's going to hold up to modern opponents and I'm going to have to splash the £££ on an active weapon...
As for screwholes getting weaker. Don't think I'll get that issue, as i'm planning on basically holes with bolts running through it, and everything held in place with nuts. Although I'm not sure how much i can do with just that, and i'm not sure how flimsy that sort of design would be when it came across a violent throwing into a wall. Only one way to find out for sure I guess. Trial and error!
21st April 2017, 17:21
Perun, our raptor, is milled out of a massive billet of HDPE. (doable with a router)
The lid is held on with bolts right trough that block.
21st April 2017, 17:52
wedge all around... now i'm thinking of a design many full body spinners have.
Sure good to deflect blows, and sacrificial HDPE is.. well... that stuff is, compared to anything else useable in that weight class really cheap. if you even shock mount the electronics, that will be one shell hard to open.
Only problem: what happens when you get upside down? you'll need to either stick the wheels out through the top (needing bigger wheels) to drive on your back if needed (but the wedge would be turned around then, too). Or get some self righting arm or such to pop up.
Well, not really need, but would sure be a good addition if something gets under you and turn you around, since as mentioned pure HDPE-wedges get blunt fast, so you don't have much hope to get under another pusher, flipper, lifter etc. Even many spinners stay low to the ground as defense against these.
Anyway, the way i see it the meta is like this for now:
big spinners, have massive energy stored and causing others to really think about their side armor.
heavy armored pushers to charge into the spinners before they spin up and push them into the pit or whatever.
flippers to get anybody who isn't low to the ground and get a self righting arm or can drive on both sides.
Hammers/Axes to remind everybody top armor is needed, too.
grabber, lifter etc. for everybody trying to have an active weapon, but maybe easier to build than these high powered ones.
Crusher... just the occasional few to remind people internal structure is needed, too.
And at least from the one event i saw that's also about how often they appear/how dangerous they are, from top to bottom.
(But that one was in germany, so might be different for you).
Anyway... something well armored and able to push definitely is competitive, if you can drive it well. And that just needs practise.
Your motors won't even have to be too powerful, since mostly traction is the bigger problem. And getting really good wheels... well, there are some threads about that, a science in itself.
So with that design:
A inner shell, as compact as possible from thin HDPE to house the electronics.
And around that the wedge with some air pockets. sounds good to me.
- weight. Wedge in all directions needs a lot material or steep wedge. But can be done, if no active weapon needs weight.
- most wedges have two driving wheels somewhere in the back, and one point of the wedge (or close to the wedge) slide over the ground to stay as low as possible. could be interesting to get all sides low.
- if someone get under you, you'll be left with wheels in the air as soon as one side leaves the floor (since the opposing side gets stuck on the floor, wheels will hang in the air between them). So no way to retreat and free yourself.
- pure HDPE wedge doesn't hold up long, possibly add a steel tip to it. nothing fancy, maybe like this? http://forum.roboteers.org/gallery/u...48e3-large.jpg
- what to do when you're upside down?
21st April 2017, 18:35
Cheers for the reply Runsler.
I completely forgot that if the bot is upside down, the angle is reversed and doesn't have any effect on bringing down potential damage from spinners, oops - that minor oversight ruins the whole running upside down thing. I find that sometimes the best defense against spinners is to be as quick as possible and ram them front on before the spinner has time to get up to a meaningful speed, and push them around from there. Although some spinners get up to speed incredibly quickly compared to some. That tactic is more than likely a "do or die" scenario. Either it works, or you get torn to shreds.
I think i've also worked out a schematic where I can control it using an Arduino, and to keep costs down incase replacements are needed frequently, wouldn't even need to be a genuine Arduino, just a compatible clone you can pick up for $5 - I've used a few clones and never had issues with them.
Steel tip sounds rather good, although I'm not sure how i'd do that, I'd need to look up stuff moreso than the rest, as i've literally never worked with any metals before.
Last edited by Redirect Left; 21st April 2017 at 18:41.
21st April 2017, 19:15
Make the wedge from HDPE.
Take a sheet of steel , and screw it on the HDPE in a way it is a bit longer where the tip will be. now if you want, you can try to sharpen it (from the floor side, to keep the angle sharp) a bit more, but that's all you'd need. And it doesn't have to be a big sheet, maybe more like a stripe.
Some shops get you stuff like that cut for really cheap, or you could ask a local metal working company (not the really big ones^^) to do that for you, and also let them make you a few spares.
I would only use that on front and rear end, since the wedges on the sides are defensive, you can't really use them to get under someone. There you can also get a little bit closer to the floor, since you won't get stuck with the sides as easily as with something in driving direction. So no use to keep them as sharp.
Another idea: it would be a bit more complicated, but a lot more effective to make the base plate octagon shaped, not square. just to avoid the 90° angles on the wedges, the smoother and flatter those are, the less the spinners got to bite into. but i'd treat that as extra, depending on how you can work with the material and stuff like that.
Plus, if you're going to use an arduino anyway and like electronics... possibly ask Rory Mangles how he made Nuts spin around and still be controllable. i could imagine this working for your bot, too. But again, that's an extra that would effectively convert a push/wedge bot into a full body spinner. And then you'd need fast motors^^
ps.: well, it would still have some effect against horizontal spinners, they'd make you go up (possibly turning you back again) and, depending on their balance, maybe make their blade go into the floor... whatever effect that may have, depending on the bot.
vs. horizontals... if they're weapons radius is bigger than your height, they'll land a big hit, definitely flipping you (but how often) and bend or rip the wedge on that point. If their weapon is smaller, they'll scrape on the wedge just like they did when you were the other way round.
Last edited by Runsler; 21st April 2017 at 19:20.