Team Antiquarian new build diary

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MySolderIsOlder
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Team Antiquarian new build diary

Post by MySolderIsOlder »

Having got past the mad pre-Christmas rush to build four ant-weights plus arena 'for domestic use', I've now settled down to a more sedate design/build cycle - one where I can learn from my many previous mistakes and have a bit more fun. First of these new generation bots is an invertible wedge/pusher. We were going to call it "This way up" but then we saw from one of the AWS videos that someone had already nabbed that name - so now I'm thinking "Other way up" or "Any way up" (anyone know if those names have been used yet?)

Anyway, basic design is a 45-degree parallelogram, with the wheels mounted off-centre, so that whichever way up it is, it's always tilted down at the nose.
Construction is using my preferred combination of 4mm polycarbonate sides with 1.5mm top/bottom armour attached with M2 machine screws.

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BTW, that silvery tool next to the Wera hex-driver is an M2 tap mounted in a pin-vice. Once I've pre-drilled a 1.6mm hole in the thicker polycarb (much easier since I got my hands on a Dremel drill press), it only takes about half a minute per hole to cut the threads.

In a slightly wonky side-view, you can see from the 30mm ToughHub wheels how the motors on the left are mounted 4mm higher than the ones on the right (i.e. at the back) - just as it would be the other way up. Took ages mucking about in Fusion-360 to work out the right dimensions but the end result means the 'attack' end is always within a mm or so of the arena floor.
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My standard power switch cum bind/charge port sits to one side, tucked in behind the front wheel. Attaching to the inside of the 4mm polycarb means the switch is just flush with the surface, so minimal risk of accidental cut-off. The machines screws are mostly M2, 6mm button heads from ModelFixings.co.uk, but I used the countersunk version on the front to keep a smooth finish.

Top-view shows the necessary spaghetti, as well as the cut-outs for the wheels. For these, I just drilled the corners to avoid splitting and then cut each side with very sharp wood-chisels. Battery is the last of my Vapex NiMH 120mAH 6v packs (sadly no longer available).
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From underneath, you can see the 2/3S 5A Dual ESC (ten quid from AliExpress), which is wired to an OrangeRx R614XN DSM2 nano receiver (annoyingly, these are currently out of stock at HobbyKing), all wrapped in silicone tape and held down with a dob of hot-melt glue. You can also see the polycarb mounting plates I used to get the motors at the right height (5mm thick plate at the front, 1mm at the back)
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I always knew I'd need something sticking out either side to stop it getting stuck on its edge, so deliberately kept the overall width of main body to 90mm. Then all it needed was a tapped hole either side and another M2 screw, with a lock-nut to keep it tight. As a result, no matter how you drop it, it always lands on all four wheels.
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Final touch is a strip of acetate at each end so it just scrapes the arena surface;
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Great thing about a parallelogram wedge is that you don't have to reverse the controls if it's flipped over - you just spin it round and attack with the other end.

End result is fun to drive, though a little manic - it's going to take us a while to get used to the speed with those 500rpm motors but it steers well and holds a straight line. Slightly over-weight at 157g, although if we ever come to an event, I'll switch the NiMH pack for a Turnigy 2S Nanotech; that will save 4g and it shouldn't be difficult to shave off another 3g with a few holes drilled in those somewhat over-engineered 4mm side panels. Indeed, if I really thought about it I could probably shave off enough from the bits that don't matter to add some spinner-friendly strips of 0.5mm titanium to the vulnerable parts of the wedges.

Right... NEXT!
Stuart (Anthony's dad)

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MarkR
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Re: Team Antiquarian new build diary

Post by MarkR »

That is really nice construction using tapped holes and machine screws, instead of self-tapping :)

Good write-up too
Robots: Betsie - RaspberryPi controlled flipper bot with gyro stablisation - too clever for her own good?
Stacie - tidy flipper; 4wd driven by hair bands

MySolderIsOlder
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Re: Team Antiquarian new build diary

Post by MySolderIsOlder »

Thanks Mark. I had previously experimented with self-tapping screws but kept having problems with heads shearing off. Hence why I started experimenting with tapped holes. Really amazed how strong the joints are, even with just M2 size. Other pleasant surprise is that even where I've had to screw/unscrew joints a dozen times, I've not yet had any issues with the threads degrading or becoming loose. All down to the magic properties of polycarbonate I guess.

Anyway, good luck to everyone going to the AntFreeze tomorrow. Hope no one gets held up by the actual freeze - and fingers crossed we'll be able to make it to an event some time this year!

Stuart
Stuart (Anthony's dad)

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Spin(d)oza got new boots!

Post by MySolderIsOlder »

From my first batch of antweights, the definite runt of the litter was Spindoza. This was intended as a simple and durable push bot with big wheels and a front scoop that pivots freely around it's mid-point (so it always stays flush on the ground, even if the wheels are out of true and absorbs some of the kinetic energy from any blows that land off-centre).
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Unfortunately those Pololu 42x19mm chunky wheels, though great on carpets, turned out to be utterly useless on a smooth arena surface. Problem is that the natural rubber is just too hard, so they skid around with naff-all traction. Where to find an alternative with more grip and pushing power? Well, I'm still not ready to go down the 3-d printer route and previous attempts at moulding silicone for fishing lures always ended in messy disaster - so it was back to basics for my 'old-skool' slicks:

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Those tasteful red tyres are sections of silicon hose-pipe, of the sort sold to hot-rodders for car engine upgrades. 26mm internal diameter, reinforced walls, a nice sticky silicone surface and available in a range of hot-hatch-friendly colours! Hubs were cut from a 1" wide Nylon rod and drilled out using a 22mm Forstner bit, so the N20 motor gearbox can sit inside it. That meant having the motor mounts further back but a little tape underneath helps keep it all tightly gripped.
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A few holes drilled through the Nylon hub, both in the end and through the sides helped reduce the weight further and a 3mm hole in the middle accepts the motor drive shaft. To stop it slipping, I drilled a 1.6mm hole at right angles, through the wall of the wheel hub, then tapped it to take an m2 grub screw that locks against the flat side of the shaft. End result is very secure but easy to remove when needed.
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To my surprise, with some judicious drilling-out of the hubs, I managed to get the weight of the finished wheels a few grams lighter than the Pololu versions (~16g instead of 19g) - which gave me scope to replace the original 2mm polycarbonate scoop with a 1mm titanium version. Once I get some suitably fine-grits for the belt sander, plan is to grind the edges of the scoop so they run absolutely flat on the arena floor. If I can get the angle right, should be just as effective as acetate. Should also make pretty sparks if it ever meets a suitable spinner :lol:
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As before, the scoop can rotate freely around that central mounting, so it always rests flat on the deck.
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Total weight with a 230mah 6v NiMH pack is currently 152g but with a 3S Turnigy nano LiPO, it'll be well under the limit and will have even more pushing power.

Need to do a lot of testing but first outing against 'Other way up' was promising; Spindoza's 2-wd with big slick tyres was more than a match for 4-wd on tough-hubs. Obviously remains to be seen how these slicks would do on an arena surface littered with debris after a spinner fight (might have to try cutting some rudimentary treads - or just fit a broom to the scoop...)

Anyway, reinventing the wheel has got me on a roll so to speak, so now looking to refine the process further and have been improvising some jigs to help cutting and drilling the hubs, etc. Managed to get a length of 1" wide Acetal rod very cheaply on eBay and that is proving much easier to work with than the nylon (went for POM-C rather than Delrin/POM-H as the latter is apparently less dense at the core, which is where I need the most strength for the axle mounting). Lots of experiments coming up with different tyre widths and different wall thickness on the hubs.

Next challenge will be to make a 4wd pusher version using this type of wheels, without blowing the weight limit!
Stuart (Anthony's dad)

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Re: Team Antiquarian new build diary

Post by MySolderIsOlder »

Well that was a bad idea! The slick silicone-hose wheels looked great - and worked great for the first few minutes. But once they picked up even a hint of dust, all traction disappeared. In a fighting arena, that design will be utterly useless - so reinventing the wheel is now on hold until the day when I get my own 3d printer!
Still, nothing ventured...
Stuart (Anthony's dad)

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Kyro
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Re: Team Antiquarian new build diary

Post by Kyro »

could you not file or cut some groves into them to create a tread? simple solution possibly? i had similar issues with the first version of dominus which had about 1 inch wide slicks which gripped great for the first minute at the last aws... thing is, they originally had tread but i decided to make them slicks with my bench grinder because "racing cars grip best with slicks"

the pololu tyres i use and the fake pololu have groves on which keep the grip at its best for longer i have found on my arena (comparing newer fakes to older worn fakes that are almost slick) so i would go for deeper grooves if possible
Team Rocket
Esper(4wd flipper)
Mantis (4wd grab 'n' lift)
Dominus (Vert SPINNAAH)
Breakout(modular cluster)
Remembering Rex (antweight cassius)
Fennec (4wd flea) former world champion

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Introducing PolycarbonAnt

Post by MySolderIsOlder »

With AWS 58 approaching fast, I thought it was about time I made a couple of antweights for my own team, rather than just for my son.

So here's my first entrant - PolycarbonAnt - a rough and ready, hard-wearing 4wd invertible pushbot, hand-bodged out of (predictably) polycarbonate.

Emphasis very much on simplicity and durability. Without tempting fate too much I reckon this should be able to survive being bounced around the arena a few times by those savage spinners.

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Side and end pieces are 6mm polycarb, with 1.5mm for the top and bottom plates and for the scoops at either end. It's mostly held together with my usual pre-tapped holes and M2 machine screws.

Wanted to keep things simple so I didn't bother with a bind/charge port this time. Instead, the battery is held by this simple slide-out caddy (strip of 0.75mm polycarb). Stops the battery rattling around - and I only have to undo 4 screws before sliding it out the side, rather than the 10 screws needed to remove the whole top plate. The protruding screws are also to stop it getting stuck on its side.
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Controller is my 'Poor Man's Nano', as described elsewhere in the "Follow up on Digital CR Servo Board ESCs" thread
(viewtopic.php?f=1&t=2884). This one is using a pair of the Feetech FT90R 'long board' controllers with a RedCon CM421 2-channel DSM Rx.

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Controller and cabling are held in place with blobs of hot-melt glue, just to stop things rattling around and breaking loose.

This is my second (and much simpler) attempt at a parallelogram-style double ended pusher and probably won't be my last - I really love that the driving controls don't change when the bot gets flipped over.
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End result is pleasingly compact - fits into my 100mm cube very easily, so plenty of room for adding acetate to either end.
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Done a few drop-tests onto hard floors and it bounces back like the proverbial Nissan Pick-up.
Only obvious weak spot are the wheels (Shakey's 25mm tough hubs), which are a perilously exposed to side attacks from a spinner. Might add some protection (got a few grams to spare) - or I might just adopt the Sontaran stratagem and assume I'll always be facing my enemy (but maybe bring spares, just in case!)
Stuart (Anthony's dad)

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Re: Team Antiquarian new build diary

Post by Ant Ipodean »

Re the silicone tubing tyres ..
Very nice. It would be interesting to try making them say 4 or 5 mm wide.
Many people think that more surface area is better, but basic physics states that total friction between two smooth surfaces with a given downforce does not vary with area.
They see the benefit of wide tyres on racing cars, but there are a lot other things going on there with surface textures.
Mike.

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Re: Team Antiquarian new build diary

Post by MySolderIsOlder »

Hmm...
Some interesting thoughts there. Might not give up on the silicone tubing tyres just yet then, least not until I've done some more tests (narrower tyres and/or cut-in treads).
Thanks guys.
Stuart (Anthony's dad)

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FoxFire
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Re: Team Antiquarian new build diary

Post by FoxFire »

I reckon you've got a nice neat and compact machine there - looking forward to seeing it in action at the upcoming AWS! I started cutting my own polycarbonate panels this year and it is wonderful stuff to work with for this weight class. I have thought about building a chassis of my own with lexan for a possible fleaweight.
Mark Smith - Team Frey
Polaris (Front Hinge Flipper)
Proxima Centauri (Rambot)
Sprocket Raccoon (Lifter/Rambot)
Fighting Fox (Flipper)

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