Team Antiquarian build diary

All things antweight

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MySolderIsOlder
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Team Antiquarian build diary

Post by MySolderIsOlder » Mon Aug 06, 2018 12:45 pm

Hello everyone. Here begins yet another newb's build diary. Apologies if it's only updated erratically - always tricky to find time!

Thanks for reading,
Stuart
-----------------------------


As a bit of backgound, I want to make around 4-6 antweights plus an arena for my son's 8th birthday/Christmas present. This is partly so he and his friends can have fun fighting their own robot wars and partly to get him even more hooked on electronics and engineering. I'm hoping that once this initial batch of bots is out of the way we'll then be able to work together on more competition-oriented antweights (and ideally get his school involved, since they have a great ICT dept). Eventually I will probably invest some time and money in a 3-d printer but for now I'll make do with what's in my garage/workshop, which is set up for general DIY and carpentry, rather than delicate model making and electronics. I'm a natural bodger - prone to making things that are highly effective but usually inelegant and over-engineered, so the antweight rules are potentially my worst nightmare!

However... after reading through myriad posts on here and elsewhere, I started assembling the bits for a first prototype . Picked up a few N20 motors, wheels, cabling, switches, NiMH batteries, etc from various sources and also a Sabretooth 2x5A ESC (I know - expensive and too big/heavy for an Ant - but it was an easy option to start with and I may try building something bigger with it one day.) Next step was the R/C transmitters. After a lot of lurking and some sharp bidding, managed to pick up a couple of Spektrum DX6i's on eBay for reasonable prices. One of those came with an Orange receiver, so as a 'Proof of Concept Bot', I plugged that into the Sabretooth, wired up 4 motors and a 6v battery, bent some aluminium sheet into a rough box shape and plopped everything in. To my utter amazement it all worked first time. Incredibly gratifying to see PoC-Bot trundling around the workshop in response to the joystick movements. This was the first time I'd ever used a proportional controller (rather than those very skittish little 'all or nothing' cheap r/c toys) and it's amazing how much more responsive it is. Unfortunately PoC-Bot was more SUV than antweight - but it was enough to make me believe I might actually be able do this.

So, initial rush of blood out of the way, it was time to start on some more practical builds. Vague plan for the fleet is two flippers, two pushers, plus maybe a spinner and a grabber. With three bots bound to each transmitter that makes for plenty of one-on-one combat options for the kids. Nothing too destructive at this stage as it all needs to be safe enough for sensible 8-year olds to play with on their own (which is also why, for now, I'm sticking with NiMH battery packs instead of liPOs.)

Found some nice little Redcon 4-channel receivers on Banggood which are cheap, small, lightweight and seem to work perfectly with the Spektrums, so I invested in half a dozen of those. ESC options are less simple. Although half a dozen NanoTwo's would be the dream solution, it would presumably exceed Shakespearean production capacity and hardly be fair on anyone else. Of the various alternative ESCs I've seen recommended here, it was a nightmare distinguishing between the different versions of what may or may not be the same product being offered by myriad on-line sellers at wildly different prices. First up I tried a couple of generic single-channel 10A reversible ESCs but these were the 'with braking' option and I found that going from forwards to reverse required an awkward down-up-pause-down stick maneuver, somewhat akin to double-declutching - so that was a non-starter. I have a pair of the switchable Bustophephedons coming on a slow boat from China so will have to see if I get on any better with those when the brakes are off.
For now however, I'm concentrating on the dreaded DasMicro 256A. First challenge was wiring it up. Although I was very into electronics as a kid, I drifted away from it in my teens and consequently I've not done any soldering since the days when ICs were a novelty and staying within the tracks of a Veroboard was seen as 'finesse' work (also a time when my eyes were a lot sharper and my hands a damn sight steadier than they are now!) Tiny surface mount soldering pads on a postage-stamp sized double-sided board are a whole new ball game! Might have helped if the croc clips on the blue plastic 'helping hands' tool I'd bought didn't spring back half an inch every time I positioned a wire for soldering (can anyone recommend a good make of *really* helpful hands which stay where they're put?) Eventually, after a few retries and a lot of swearing I got it all together - and although the soldering looks hideous and I got two of the receiver wires back to front (it's OK as long as I remember to reverse the plug at t'other end), there are no bad joints or crossed tracks. Plugged it all together, taped the motors to a cork block, bound the receiver and tested with the transmitter. Everything seems to be working perfectly with no glitching or overheating. Incidentally, I did find one use for the little capacitors that ship with the DasMicro, even if motor sparking is unlikely to be a problem at this level; if you thread the cap's leads through the tiny holes in the motor's solder tabs (so the cap sits in the middle), you can bend the leads into little 'bunny ears', which are much easier for a novice to solder the heavier ESC connection wires to.

As an aside - I have two practical questions at this point which I'm hoping one of you experts may be able to help with...
1) Given Das Micro's reputation for burn-outs, plus my fondness for changing designs around, I'd like to make the motor connections pluggable instead of hard-wired. I have some JST (XH) male/female connectors pre-wired to 22awg cable. I was thinking I could solder the female side on short leads to the DasMicro and the male-end wires to the motor terminals. That way I can easily swap out an ESC if it fails. Question is, are these connectors up to the task or do I risk overheating when driving flat out?
2) Given the obvious physical weakness of surface soldered wires (especially when soldered by an old bodger like me), would it be OK/advisable to smother the connections (or even the whole board) with Araldite? Sort of like a poor-man's potting compound...

Anyway, with the basic electronics sorted, it was time to move on to some bodywork. Although I can just about manage cutting and bending sheet metal, polycarb seems to be the lightest option - so ordered some cheap A4 sheets of 1.5mm Lexan and dug out the aviation snips. Decided to start off by making a prototype wedge flipper. Never intended as a serious contender - rather just a chance to experiment with construction techniques - and given my lack of experience with polycarbonate, it soon earned itself the name "Flippin' Ugly".
I started out with a cardboard template - and once I was happy with the shape, traced this onto the Lexan and cut it out with the snips. Didn't have much luck bending it cold but gentle warming with an el-cheapo small heat-gun made this much easier (when I try this for real I might make a wooden 'last' first to bend the plastic around and hold it secure when drilling.) Because I didn't have any nuts/bolts smaller than M3, I decided to use some old-fashioned pop-rivets I had laying around from a previous DIY project. Although these may be frowned upon in proper metal-working circles, pop-rivets turned out to be surprisingly good for joining thin polycarbonate. Quick, cheap, easy to use and very light (aound 0.3 grams per completed rivet, compared with 0.8 for my smallest M3 nut & bolt).
Although the end results are grotesque and very uneven, it did only take a couple of hours to cut, drill, bend and join my first flipper body. Just to make it even uglier, I used an old brass cabinet hinge for the flipper, again fixed with pop-rivets. Dropping in all the electronics for a weigh-in, "Flippin' Ugly" tipped the scales at 128g, which leaves me ~20g for the top-plate, flipper linkage and servo mount. Now all I need is a few hours of free time to finish it off...

Image

Lessons learnt so far:
1) 150g is a LOT less than you think (I may relax the weight limit for the Christmas present bots, though I want to do at least two that are competition-legal)
2) 1.5mm Lexan, though easy to work, lacks rigidity. I'm worried about how much of a flipper/weapon's kinetic energy will be wasted on bending the bodywork to which it's attached. For my next experiment I may try making a frame from 3mm instead as I seem to be able to bend it quite precisely with careful heating - and it takes little self-tapping screws beautifully (hard-drive mounting screws work just right). Better still I have loads of old sheets and offcuts left over from various DIY projects. I can then use 1mm Lexan for the skin.
3) Battery packs REALLY don't like being short-circuited, even if you do it accidentally. Forgetting that lesson (twice) was painful, messy and (with 4xAA Duracells) rather smelly. This is why I will NEVER cut through NiMH battery pack leads like that again and NEVER leave bare ended leads connected to the battery holder when I drop a half-finished experiment back in the box.
4) Leads of any sort in an antweight are always too long - up until the point when they're too short. There is no happy medium.
5) Without this forum and the generous info-sharing of all its member, I wouldn't have stood a chance of getting even this far!
Attachments
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3 pop time.jpg
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Last edited by MySolderIsOlder on Mon Aug 06, 2018 3:14 pm, edited 4 times in total.

MySolderIsOlder
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Re: Team Antiquarian build diary

Post by MySolderIsOlder » Mon Aug 06, 2018 12:54 pm

(sadly one thing I haven't yet mastered is uploading pics to this forum!)
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MySolderIsOlder
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Re: Team Antiquarian build diary

Post by MySolderIsOlder » Mon Aug 06, 2018 1:22 pm

6 riveting detail.jpg
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5 heat gun.jpg
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MarkR
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Re: Team Antiquarian build diary

Post by MarkR » Tue Aug 07, 2018 8:03 am

Looks very good.

I like your idea of smothering the Dasmikro pads with epoxy or something, to improve mechanical strength. That is probably what went wrong with my Dasmikro- after unsoldering and soldering a couple of times, I managed to lift one of the tracks slightly and create some kind of short which made it go pop!

Connectors sound like a good idea, there are those little molex-type ones which are super small (not sure about current ratings). The problem is that the Dasmikro won't have any way of mounting the connectors on the board, I suppose, very short wires + blob of glue might do it.

I also like the idea of using rivets - I've never riveted myself, but it seems like nicer and easier than fiddly tiny nuts and bolts which get lost and damaged. (PLUS M2 bolts which are always too long, and shortening them is a pain)
Robot: Betsie - RaspberryPi controlled flipper bot with gyro stablisation - too clever for her own good?

T_Y
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Re: Team Antiquarian build diary

Post by T_Y » Tue Aug 07, 2018 10:09 pm

Looking nice, your son and his friends are bound to enjoy battling little antweights!

Regarding connectors, I think they should be fine. In one of my bots, everything has Dupont connectors with 22awg wire (aside from battery connection which is JST), and I haven't had any problems so far. It's worth considering how much space those connectors will take up though - I had to redesign the shell larger in order to fit everything in.
Thomas
Hello, World! - Antweight Front-hinged flipper
Percussive Maintenance - Antweight 'axe'bot (rebuilding)
Have You Tried Turning It Off and On Again? - Antweight 4-bar lifter (designing)

MySolderIsOlder
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Re: Team Antiquarian build diary

Post by MySolderIsOlder » Wed Aug 08, 2018 11:07 am

Thanks for those comments. - very helpful. Got me thinking about more compact ways of making the motor connections (you're quite right - even on short leads, the JST XH in-line connector pairs are a bit long and may cause problems fitting into an antweight).
Next option I plan to experiment with is the Molex KK396-type pcb headers. They have a 3.96mm pitch, which by my measurements looks conveniently close to the motor pad spacing on the DasMikro. Obviously can't do 'pin-through' but I reckon it should be possible to solder a 4-pin KK396 straight header flat against the 4 solder pads, then secure the header's body to the edge of the board with plenty of epoxy. The motors can then be wired to 2-pin crimp connectors (the Molex housings are ~15mm long) - though the connectors are keyed so of course one motor in each pair would need the wiring polarity reversed. You never know - it might work...

Got some of the relevant Molex headers on order so will report back with results when I've had a chance to try it.

Cheers,
Stuart

Ant Ipodean
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Re: Team Antiquarian build diary

Post by Ant Ipodean » Fri Aug 10, 2018 5:23 am

I have used the JST connectors for motors, and cut away the outer plastic shield around the pins on the plug. This "depolarises" (is this a word?) them to allow easily changing motor polarity.

Mike.

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Re: Team Antiquarian build diary

Post by MySolderIsOlder » Mon Aug 13, 2018 8:11 am

So the Molex KK396-type pcb headers arrived and I found time over the weekend to solder one on to a DasMicro board, just as an experiment. Turned out to be pretty easy, even with my terrible soldering technique. Trick was to get plenty of solder onto the surface pads and the header pins separately first, before trying to join them. Oh and I ditched the fancy modern bendy arms 'helping hands' to go back to a cheap, old fashioned version (solid bar with ball & socket mounted croc clip at each end) - so much better!

On the plus side, the header pins fit the solder pads almost perfectly. If I was sticking with this solution, I'd run a line of epoxy all along the boundary between the board and the header. Should be possible to effect a really solid joint there.
Molex296-1.JPG
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I wired the board up to test it. All worked fine - but in the end I decided I wasn't keen on the added bulkiness and it makes it harder to wrap the board in heat-shrink tubing. Instead, I desoldered the header and moved onto plan B.

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Re: Team Antiquarian build diary

Post by MySolderIsOlder » Mon Aug 13, 2018 8:25 am

After playing around with trying to fit the various components into a small space, I decided life would be easier if all the cables were emerging from the same end if the ESC (well, I see from pictures that the wires on the Nano do, so it must be a sensible design feature!)
Having abandoned the Molex header experiment, it was back to the JSTs. Only this time, I soldered the motor leads facing the other way, before applying plenty of araldite...
DasMicro-1.JPG
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Here it is with the heat-shrink (having burnt out a battery pack during early experiments when the ESC was pressed against an aluminium case, I'm now obsessed with heat-shrink tubing) and all the connections, including the little sub-5 quid DSM2 Redcon receiver:
DasMicro-2.JPG
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And finally, everything wired up in my little Lego test-bed. Works a treat.
DasMicro-3.JPG
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Will have to see how it survives in combat situations but I ran it continuously for a few minutes and no sign of overheating. Now I've got a design I'm happy with, I'll wire up a few more of the DasMicro boards in the same way - same connectors and lead lengths/positions. That way it should be easy to swap out units if/when they do ever burn out.

Next jobs is to fit it into Flippin' Ugly.

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Re: Team Antiquarian build diary

Post by MySolderIsOlder » Mon Aug 13, 2018 8:39 am

Finally time to finish off my first prototype Antweight.

The big brass hinge had to go - simply too heavy and it was in the way. Instead, I made the top flap with little tabs that I drilled and bent over, then attached to the main body with M3 bolts, using plastic-insert nuts so I could keep the hinge loose. Hummed and hah'd a long time about how to attach the servo before opting for the simplest possible solution; four small holes and two cable ties. Then cut and drilled a thin strip of lexan and bolted it on to the standard servo arm:
FlippinUgly-1.JPG
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Took a bit of experimentation to get the arm lined up so it would be parallel with the flipper lid when the servo was neutral but got there in the end.
FlippinUgly-2.JPG
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Here it all is with everything in place:
FlippinUgly-3.JPG
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Total weight was 151.3g. If Flippin' Ugly was a keeper I could easily save some weight by shortening the servo lead and using lighter bolts on the hinges but since this was just a prototype, I shan't bother.

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Re: Team Antiquarian build diary

Post by MySolderIsOlder » Mon Aug 13, 2018 8:51 am

BTW, In the spirit of 'keep it simple, keep it safe', here's the hi-tech flipper-return mechanism - just a length of 'powergum' from my sea-fishing goodies box:
FlippinUgly-4.JPG
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FlippinUgly-5.JPG
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Having messed about with Flippin' Ugly, several lessons were learnt:
1) The wheels need to be further back. Ideally right at the back and protruding out of the rear of the case. Otherwise it keeps falling over backwards and the flipper won't go back far enough to self-right.
2) The 600 RPM motors I used for this experiment were way too fast, bot was far too skittish during the brief periods when it wasn't lying flat on its back.
3) My wedge shape was way too tall - I could have made it half the height and still fit everything in. Next one will have a much sharper triangular section, which should more stability as well as making it easier to get underneath an opponent.
4) I need to be a lot more precise with measuring, marking and cutting -and especially with the bending. This first test was largely done by eye, working from a rough cardboard template. For the next one I want to work everything out with a CAD tool first. So... time to learn Autodesk Fusion 360 (which will also come in handy when I eventually treat myself to a 3d printer.
5) This is FUN! Haven't enjoyed problem-solving so much in years.

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Re: Team Antiquarian build diary

Post by MySolderIsOlder » Mon Aug 13, 2018 9:02 am

BTW, this was my very first (and very heavy) attempt at at robot - the Proof of Concept, or 'PoC-Bot'. Smiley face was added just so driver knows which end is forwards. Eventually he may gain a lifter/flipper arm one end, a bucket the other and a Pi or Arduino board in the middle, before being reborn as an autonomous 'house robot' - but that's a longer term project. I'd also have to find a reliable way to stop those pimoroni moon-buggy wheels falling off so readily...
PoC-Bot.JPG
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EddieJ
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Re: Team Antiquarian build diary

Post by EddieJ » Mon Aug 13, 2018 10:54 am

Looking great! Im envious of your speedy progress :D Wish my projects moved this hastily forward
I always love the look of see through bots like this. Definitely agree you can lower the wedge angle. Good luck with the next steps!

Dazmund
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Re: Team Antiquarian build diary

Post by Dazmund » Mon Aug 13, 2018 10:11 pm

Nice work so far! I just wanted to ask if you're sticking to the 4 inch cube rule on the size of your robot? I'm asking because you actually don't need to have the robot sit square in the cube. My own robot is 4 inches wide, 2 inches high, but 5 inches long, but it'll still fit in the cube if I laid it on its side within it.

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Re: Team Antiquarian build diary

Post by MySolderIsOlder » Tue Aug 28, 2018 1:23 pm

Having spent a few weeks mucking about with ideas and test-beds, I decided it was time I got at least one of the half-dozen antweights I hope to build before Christmas finished. So... without further ado, I give you...

"Shove-All"


(this is my first attempt at embedding imgur image-links, so fingers-crossed...)
Image

I had a Pololu Zumo chassis lying around from first attempts at making an R/C bot. An unfortunate incident with some bare leads shorting on something metal while it was sitting in a pile of junk on the bench resulted in four very angry AA Duracells and a plume of smoke, which rather messed up the Zumo's battery holder (as well as stinking out the workshop). So in search of a quick win, I dug the remains out of the scrap pile, cut away the damaged or superfluous bits and bent what was left back into shape with the help of a hot-air gun. Then I roughly cut and drilled a piece of 1.5mm Lexan to replace the singed top. I've used the original Zumo 1mm steel shovel (hence shove-all) blade as a pusher. With some careful adjustment, the top sits fractionally below the upper track surface - so it still gives good front protection but the bot can drive happily upside down if it needs to (which compensates to some extent for the lack of any self-righting mechanism).

Image

Innards comprise 2x100rpm generic N20 motors, DasMicro 2S6 ESC, Redcon 4-Ch DSM2 receiver and a Vapex 120mah 6V Ni-MH battery. Bit of a squeeze but it all went in eventually and for now it's still possible to use the original clip-in hatch on the bottom to remove the battery for charging. Obviously that power switch was a mistake - in a vulnerable position and it's too big, which made fitting everything else in a lot harder than it needed to be - so ordering up some smaller replacements. Might also fit a charging port so I can then glue the hatch closed.
Total weight currently is 153g. For domestic use I'm not fussed about the excess baggage, though it would be easy to trim a few grams off and get it ant-legal if we ever needed to. Fits inside the 4" cube with loads of room to spare.

Image

Thanks to the rubber tracks and low-rpm motors, traction is v good. No trouble shoving wooden blocks 3-4 times its own weight around the workbench. Should be even better on a clean surface once I've washed all the fine sawdust off the tracks.

So, that's the easy one done. Only five more to go. Next bot is going to be a lifter...

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