Team Antiquarian build diary

All things antweight

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Re: Team Antiquarian build diary

Post by MySolderIsOlder » Mon Sep 03, 2018 3:00 pm

On reflection, decided that my "Flippin' Ugly" experiment (see above) might be salvageable, if I could lower the aspect ratio and move the wheels back a bit. So... out with the tin-snips and on with the face lift. Basically chopped off the top third of the wedge;
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Ten minutes hacking with dremel cutting disc and file to extend the wheel slots up the back of the case meant I could shift the wheels further back from the centre of gravity. Now it doesn't flip on it's back every time I drive forwards!
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Flipper hinge is just a couple of holes with an M3 bolt, nylon washers and spacers, held on by a lock nut. Simple but effective.
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While the flipper linkage is still just a simple servo-arm extension, using a length of 'Power-gum' for the return mechanism (that stuff, normally used for tying stop knots on sea-fishing rigs, has a breaking strain of around 10kg, so should be ideal for this role).
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Now I have less height to play with, fitting it all in is a bit more of a struggle (if only one could buy a Nano Two!) so I think I might try cutting/desoldering the pins on the receiver and wiring it direct to the ESC and Servo - with some kind of jumper for binding..


After an afternoon of plastic surgery, I wouldn't say that my Flippin' Ugly duckling has matured into a beautiful swan - but it does at least function as a fighting robot. It drives pretty well, can self right effectively and shift small obstacles. Best of all, it only weighs 134g - so scope to replace the generic 9g weapon servo with something that has a bit more kick. Then just need to find a more effective way of securing the innards so the stay in place and we're ready to rumble.
Last edited by MySolderIsOlder on Mon Sep 03, 2018 4:08 pm, edited 1 time in total.

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Re: Team Antiquarian build diary

Post by MySolderIsOlder » Mon Sep 03, 2018 3:55 pm

Actually managed to get quite a lot of time in the workshop this weekend (and with TMS on the radio too - sheer bliss) so I've been experimenting with alternative ways to build using polycarbonate sheets. I have some large sheets of the stuff and various off-cuts lying around, left over from DIY secondary glazing panels (used to have a very drafty house), but they're 3-4mm thick and don't bend easily. I really wanted something that would give me nice clean right angle edges. Experiments using small brackets of bent polycarb were fruitless and I don;t have a 3d printer (yet). Then I noticed the Nutstrip on Fingertech's website https://www.fingertechrobotics.com/prod ... d=nutstrip - loved the idea but didn't fancy the cost, the shipping time, nor the imperial threads - so had a crack at making my own. Ordered up a cheap 1-metre length of 1/4" square bar in 6082T6 Aluminium, drilled a series of 2.5mm holes at right angles, tapped with an m3 thread and cut it into short chunks. Not without its challenges (if I carry on with this I need to improvise some better jigs to ensure holes and cut-offs are are more reliably equidistant - and Aluminium really gums up taps) but I think the idea has potential. Very light but strong way of joining two sheets at right angles. If I can figure out a suitable drilling jig, should also be possible to have a third hole (x-y-z axes) for joining three sheets at a corner.

This is the prototype for ServAnt - a basic (cheap!) all-servo flipper that I'm using to test the edge joints. Currently looks like a bowl of psychedelic spaghetti but I treated myself to a simple crimp tool and some Futaba connectors recently, so those servo leads are facing savage cut-backs.
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Detail of an edge joint, holding 3mm Lexan sheets at right angles with 6mm m3 screws (should have used 9mm but don't have any at the mo). Obviously cut it too close the to hole on the left side, though it still feels pretty strong :
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Also using my threaded joints for the flipper hinge - obviously needs spacers and washers and a lock-nut on the end of that bolt:
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ServAnt's flipper blade is a 10cm square of 0.5mm titanium foil. Really just need to sort out the flipper linkage and it will be usable. The elephants in the room though are those blasted cart-wheels - at 60mm diameter they're far too big, so yet again my wedge is too tall. So far I've not managed to find any smaller ones that fit a continuous servo's shaft. Really need something around 30-40mm. Worst case I might try cutting discs from the end of an aluminium (or nylon?) rod and drilling the mounting holes - then improvising tyres. For the latter I did think about sticking on carborundum paper for grip but that might not go down too well with arena owners! More practically, I found some large diameter shrink tubing with an almost tacky finish that might do the job and could have great traction - but that's an experiment for another day.
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Re: Team Antiquarian build diary

Post by MySolderIsOlder » Fri Sep 07, 2018 3:25 pm

Current work in progress is a flipper called (for reasons that will become clear in due course) "Project Box Bot". Space for innards is even more constrained than usual so decided to see what I could do to slim down the Redcon 4CH DSM2 receiver + DasMicro 2S6A ESC combination. With some trepidation, snipped off then desoldered the header pins from the rx and wired direct to the ESC on very short leads. With all other leads in place, wrapped the Rx in heat-shrink first, then folder it back over the ESC and sealed the package with another layer of heat shrink. End results are satisfyingly compact - positively elephantine compared with a Nano but a great improvement on my previous set-ups.

Blue & yellow wires are for the two motors (controlled by AILE & ELEV channels on the Rx), red JST connector on the left is to the battery input, black socket on left is female servo connector (on THROTTLE channel - will shorten that lead later), while the two green wires are soldered to the normal bind terminals - plan is to connect those to a combined charge/bind port and switch on outside of the case so I don't have to remove the battery for charging.
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Close up of the ESC side of the package:
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...and the Receiver side (with the LED still visible from outside)
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Tested both motor channels and the servo - everything works fine though will be interesting to see how well it holds up in battle.

May order up some OrangeRx R614XN nano receivers next and try those, simply because it was such a chore desoldering pins from the Redcon. Bit of a fiddle to assemble but the saving in space and weight definitely made it all worthwhile.

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Re: Team Antiquarian build diary - resumed!

Post by MySolderIsOlder » Fri Dec 07, 2018 10:46 am

Well, it's been a while... I was getting frustrated by my fundamental inability to bend and join materials neatly so decided to take some time out and experiment with different construction methods. Toyed with the idea of buying a 3-d printer but given how much I need to get done by Christmas, can't afford the learning curve (not to mention insufficient funds or suitable space for one.) So decided to stick with polycarb for now but find alternative ways to use it.
As mentioned in previous post, I'd been trying to make brackets out of aluminium bar, drilled and tapped for M3 machine screws, so I could mount sheets at right angles. That idea seemed to have potential - but in the end I got fed up with the tap threads constantly clogging up with the soft metal - and it all felt a bit too bulky. So instead I decided to try using thicker polycarb for chassis parts, which I could drill and join on to with M2 self-tapping screws. Prototype build using this method is a Tracked Lifter, which ended up massively overweight (175g without a battery), so you'll never be seeing this beast at AWS. Having learnt a few lessons from this build though, I'm fairly confident I could make a Mark II that would scrape into antweight range. Something for the new year perhaps.

Meanwhile, here's TL Mark 1...

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I've used the Pololu 22-T track set, DasMicro ESC, RedCon 4-ch receiver and a Vapex 230mah Nimh battery (sadly it seems they've stopper making the little 120mah ones).


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This was also my first attempt at a 4-bar linkage. In case it wasn't obvious, the rear-hinge design was inspired by the Nuts n Bolts flipper. Main difference being that whereas Alex's flipper mechanism is beautifully optimized and neatly printed, mine is heavily over-engineered and rough-hewn out of 6mm Lexan. Does work though - which was enormously gratifying, even if most of the Turnigy's power is going into shifting all that weighty plastic.

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Nylon stand-offs on top are just to help self-righting. Without them it's a beached whale.

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The top-plate is probably thicker than it needs to be but since it's the main structural member, I wanted something that would not flex. If I ever redo this design, I'll carve out unwanted areas of that chassis with a Dremel cutting tool.
I spent ages trying to figure out how best to mount a servo until I twigged it just needed a little scrap of thick polycarb either side and some self-tapping screws. Sometimes even the smallest off-cuts can be useful!
The underside is protected (and all the innards held in) by a thinner sheet of polycarb:
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Because this current batch of bots are meant to be played with at home, I wanted them to have easily accessible power switches - but I also wanted to be able to recharge the batteries AND re-bind to one or other transmitter (so we could switch bots between the A and B teams) without dismantling anything. After a LOT of head-scratching and worrying about wiring, I eventually came up with a combined switch/charging/binding port design which I'm now trying to incorporate in all my builds. I'll include more detail of the wiring in my next post - but here's a preview.

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Basically, it's an SPDT switch super-glued to a Futaba J connector (keyed so you can't get things the wrong way round). When the switch is on, it connects battery +ve to the ESC & Servo. When it's off, it connects battery +ve to connector Pin 1 (right of picture). Pin 2 goes to the ground lead - so with a simple adapter I can use pins 1 & 2 as a charging port. Pin 3 goes to the signal pin on the receiver's Bind channel - so shorting pins 2 & 3 puts it into Bind mode.

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I've crimped up a couple of these simple adapters with a Futaba J on one end and JST/BEC on the other. The yellow lead (looped around the charge lead so I don't lose it) is another Futaba J plug for Binding.
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Main lesson from this build was that although using M2 self tapping screws into drilled polycarb is a huge improvement on my aluminium nut-strip, it does have one huge problem - unless you're super careful (and sometimes even then), the heads of the self tapping screws shear off really easily, leaving you with a real problem. Forget about trying to drill them out - in most cases I just had to grind the stump off and drill another hole. Although I tried three different types, from three different sources, self-tappers just don't seem to be as strong as equivalent sized machine screws. Luckily I had a 'plan C' which worked much better - but I'll save that for another post.

Cheers all,
Stuart

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Re: Team Antiquarian build diary (Ffythiana)

Post by MySolderIsOlder » Fri Dec 07, 2018 1:55 pm

Having given up on self-tapping screws due to the problem with heads shearing off, for my next build I decided to try cutting threads directly into the polycarb. Plan this time was to have thick side panels into which I could screw thinner top/bottom plates. Like this:
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(that's 4mm Lexan for the side and the top bar, with 1.5mm for the skin)

Spent a few quid on an M2 tap and did some experiments with different pilot-hole sizes before settling on 1.6mm. Delighted to discover that not only was tapping threads in polycarb incredibly quick and simple compared to aluminium (no need for cutting fluid and the tap threads never seem to get clogged up) but the resulting fixings are really strong. Moreover, even with cheapest M2 machine screws, I've not had a single one break on me yet. So, with my M2 tap securely mounted in an old pin vice and a 1.6mm bit in the Dremel, it was on to the next build - this time, for the sake of variety, a front flipper.
Don't have time to think of a clever name at the moment, so here is 'Front flipper yet to have its amusing name assigned', or 'Ffythiana' (although I quite like the name 'Ffythiana'. Reminds me of Wales...)

I wanted to have a low wedge shape, with the wheels as far back as possible. That meant the usual motor brackets were not an option (besides which, I'd run out). Then while fiddling idly with an N20 motor one day I noticed that there was a bit of the gearbox where a line drawn on the tangents across the two brass pillars wouldn't actually impinge on any of the gearwheels. That got me thinking about cable ties - and in no time at all I had a new favourite motor mounting bracket. Cheap (few pence each), weigh almost nothing, don't take up much space and they're very 'strong & stable'. Just make sure they cut across the gearbox in the right place or you'll be going nowhere fast.
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Having received four duds out of four in my last batch of DasMikro's, and not having the time or patience to get replacements (and since I hadn't kept all the packaging, BangGood didn't want to know), I had to revise my choice of ESCs. The one you see above is the "2/3S 5A Dual-Way Brushed ESC" that I'd bought from The Atom Club - and although it's twice the size of a DasMikro, so far it's proved a lot more reliable so for now I'm going to standardise on these. For my next build I'll try snipping off the servo pins from the receiver and solder the wires on directly. Hopefully the space/weight saving will compensate for the larger ESC.

While on the subject of electronics, here's a more helpful pic of the combined power switch and charge/bind port I mentioned in my previous post:
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The white lead is the signal wire for the bind channel. Red & black for +ve and ground - the heat shrink tubing sections in the middle are where the power supply leads are spliced in with the servo and esc leads.

And here it is with the spaghetti folded away and everything secured with another magic cable tie...
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A big problem with my previous builds has been the rather irregular/uneven shapes resulting from my inability to make straight or parallel bends in polycarb. I figured this time it might help me keep things neat if the side were actually symmetrical, so I roughed out the design in Fusion-360 (which I've started learning) then printed just the side panel life size and roughly cut it out with some space all around. I then cut two blanks of 4mm thick Lexan (with the protective films still in place on both sides), fixed them together with double-sided tape and stuck the cut-out design on top in the same way. Then just clamped the lot in a vice and cut around the pattern carefully by hand with a fret saw, finishing off with a file and sandpaper. Finally drilled a hole straight through for the front hinge, before peeling the sandwich apart (removing the protective film). Hey presto - two identical side plates. Or at least they were until I had to botch out wheel arches because I'd miscalculated the overall width... But never mind - the basic method works a treat.
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4mm sides/top bar and 1.5mm back/base.
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Top panel/flipper was originally made from a 10cm square sheet of 1mm titanium, off ebay. Was going to have teeth along the bottom lip to help grip the arena floor when flipping. I figured that if I attached the top of the acetate half way up, it could still get under an opponent but then flex during the flip. Unfortunately while trying to bend lugs to make the hinge I managed to snap them off instead - so for now I'm using 2mm polycarb. Might revisit the titanium idea though if I ever get the chance to bring this to an AWS event. If nothing else it would make pretty sparks while the spinners demolish it :-)

The nut & round-headed bolt you can see in the middle of the floor panel is a simple adjustable caster to help it slide. Without that one of the wheels was half a mil off the floor due to the flipper lip being very slightly out of true with the wheel axis. Adding that bolt makes it a tripod so both wheels are firmly grounded and although it raises the lip slightly, the acetate should compensate for that.

Note how the servo arm has a little spur off it that pushes the flipper directly for the first 15-20 degrees of its arc - after which the normal 4-bar linkage takes over. Means I can have a too-acute-to-push angle on the linkage in the resting position but more welly when it's extended. I allowed an extra 1mm of play in the elbow joint to accommodate that. Took a bit of fettling to get the right shape (and a long time before I could convince myself it was going to work) but now seem to have got it in the sweet spot.
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Detail of the font hinge (just an M4 screw threaded into a hole in the side panel). Although I'm just using bog standard M2 screws for most of the bodywork, I also got some sweet little s/s countersunk machine screws from Modelfixings for where I need a low profile. They're not cheap - but exquisitely made and perfect for joints like this where I don't want anything sticking proud of the surface.


So... that's ffythiana. Not tried it in combat yet but drives well and self rights with great gusto. Will see if I can figure out how to load a video...
With the NiMH battery it's overweight but I also tested with a nano 2S lipo and it came in at 147g - so I finally have a bot that could eventually be entered in some future AWS (assuming one ever comes within range of Kent)

Thanks for reading,
Stuart

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Re: Team Antiquarian build diary

Post by MySolderIsOlder » Fri Dec 07, 2018 2:31 pm

Not sure this will work - and it's a lousy video (iPhone clamped in a PCB holder!) but this might show Ffythiana being test driven and doing her self-righty thing on my workbench. Incidentally, said workbench is VERY dusty, hence the wheelspin. Really need to wash the tyres and give everything a blast with dust-off...

https://www.youtube.com/embed/c7PAHPMY088

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Poor-man's NanoTwo alternatives

Post by MySolderIsOlder » Mon Dec 10, 2018 9:20 am

To cheer myself up after missing out on Saturday's NanoTwo lottery (I hit the site 2 hours after Rory's posting but was already too late!) I decided to try wiring some of my little stock of "2/3S 5A Dual-Way Brushed ESCs" (https://s.click.aliexpress.com/e/sdCep9e) directly into receivers, in the hope of losing some bulky wires and servo connectors. I had previously tried something similar with the DasMikro ESCs but since those are now firmly off my list I needed to try it with their much larger replacements.
Started off with my one remaining Orange R614 Rx (below left). These tiny boards have very small holes, so you have to be careful to keep tinned wire ends really neat - but apart from that it was pretty straightforward and I'll certainly try this again when Hobbyking next have these in stock locally. With the wires folded back carefully and all wrapped up with a bit of silicone tape, the complete package is barely any larger/heavier than the ESC on its own.
The only other receivers I had handy were the cheap Redcon 4-ch DSM2 Rx's (CM421), which have a bulky 5x3-pin header at one end for servo connectors. I had previously experimented with desoldering one of these headers and it took ages to remove all 15 pins and clean out the solder holes. This time though, I twigged that I only really needed to use 6 connections (shared Vcc & ground rails, plus the signal pins for 2 motors, weapon servo and bind). The other pins could just be snipped back to the board surface and ignored. Still a chore clearing the old solder from the holes and end result was a little bulkier than with the R614 - but since the Redcons are less than a fiver each and I have a few spares lying around, it was certainly worth the effort.

End result is a receiver/controller package weighing around 12g or less (depending on how short you trim the leads), measuring 25x45mm and costing around £15. Still gargantuan compared to a NanoTwo but easier to get one's hands on.

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Spin(d)oza

Post by MySolderIsOlder » Mon Dec 10, 2018 10:03 am

Was home-alone on Sunday so decided to see if I could make a bot from scratch in one day. Up to now I've been good at starting builds but rubbish at finishing them, so this was quite a challenge for me. End result is... "Spin(d)oza". Not the most exciting antweight in the nest but probably the only one sort-of named after a 17th century Dutch philosopher. Took about 5 hours from start to finish, not counting the time I spent on Saturday soldering up the ESC/Receiver combo.

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The 'Spin' part of the name comes from the fact that the front bulldozer scoop can swivel around the central axis, where it's securely but loosely mounted on an M3 bolt. Objective there is two-fold; it means that even if the wheel-mounting axis is slightly out of true with the front (a perennial problem with my bodgy builds), it can swivel to sit flat on the arena. Added bonus is that if it takes a hit from a spinner or flipper that isn't dead-centre, then some of the kinetic energy will be wasted spinning the scoop, rather than damaging it. Leastways, that's the theory.
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Rather than using acetate I plan to sharpen the edges of the scoop so it hugs the deck.

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Base/side are cut and bent from 2mm polycarb, as is the scoop. Front plate, to which the scoop is attached, is 4mm, top is 1mm. Reinforcing/mounting strips along the edge were cut from a bit of 6mm. Everything held together with pre-tapped M2 machine screws.

Incidentally, the single biggest improvement in my efforts to bend polycarbonate came after spending £7 on a pair of these wide-mouthed mole grips;
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Heck of a lot easier to line up accurately than a vice, and you can push things beyond 90 degrees while setting the bend. Bending the 2mm polycarb with these took some effort but worked well in the end.


Those chunky tyres were the initial motivation for this build, though TBH at the moment they seem pretty lacking in grip. Will have to see whether that improves when I clean off all the workshop dust. Otherwise might try with the Pololu moon buggy tyres, for which there is just enough room.

Here's the view from beneath. Wanted a bot that worked either way up so we could get some practice driving with the controls reversed;
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Here are the innards, with the 2s/3s 5A dual brushed ESC / Redcon 4-ch RX combo mentioned in previous post...
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...and the inevitable switch/charge/bind port assembly at the back. The switch itself is just flush with the surface - so easy enough to use with a fingernail but hopefully safe from accidental activation in combat.
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Package just fits into the 10cm cube. Total weight is 156g with the 230mah NiMH battery but there's plenty of scope for weight reductions and it would be well under the limit if I switch to a 2s Nanotech LiPo.


So that's three bots totally finished, one almost there and a couple half-started. Just possible I might complete two teams of three by Christmas as per the original plan...

Stuart

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Re: Team Antiquarian build diary

Post by MarkR » Mon Dec 10, 2018 9:14 pm

It looks great, but I wonder, what is the purpose of the large electrolytic capacitor? Is it really required, or can you maybe use a smaller one?

Mark
Robot: Betsie - RaspberryPi controlled flipper bot with gyro stablisation - too clever for her own good?

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Re: Team Antiquarian build diary

Post by MySolderIsOlder » Tue Dec 11, 2018 8:53 am

Hi Mark,

Good question - Paul suggested on another thread that it's just there to absorb voltage spikes and avoid overheating, so could probably be removed. Certainly makes sense, though TBH I've not yet needed to use one in a build where space was a real issue. If you took it off and were a bit more stingy with the heatshrink, you'd be looking at a slightly smaller package of about 33x25mm. And if you sandwiched in the receiver and maybe re-soldered the power leads to face the other way, so all wires left from the same end of the package, it could be a lot neater. Might have to give that a try.
The capacitor, which is just soldered across the two battery connections, is 470 mF and rated at 25v. Probably overkill for a 2S-powered antweight, though these boards claim to be "2S/3S 5A" so maybe they're playing safe or compensating for cheap components elsewhere?
Talking of which, in case anyone's interested in the internal organs, there's two TA6586 motor drivers, a 7805 voltage regulator and a 15W204S microcontroller. Here's what it looks like with the shrink removed - the slide switch bottom right is the mix mode. Any ideas what the two unused solder-through holes next to it might be for?
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Re: Team Antiquarian build diary

Post by MarkR » Tue Dec 11, 2018 10:25 am

That looks like a robust ESC, it's a shame the holes are too small for your wires. (I hate wires soldered to pads, it probably wrecked my Dasmikro and many others' too)

The TA6586 seems literally exactly the same part as the RZ7899 I'm using, except it is a pin-through-hole DIP version. I use the surface mount rz7899 and it seems good (time will tell) - it hasn't been seen any battle action yet :)
Robot: Betsie - RaspberryPi controlled flipper bot with gyro stablisation - too clever for her own good?

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Re: Team Antiquarian build diary

Post by MarkR » Tue Dec 11, 2018 10:28 am

Yes the datasheet does specify a 470uF electrolytic, so technically there should be two (one for each channel) but in my design I just used a surface mount 47uF and it seems to do the job - at least, it smooths the spikes enough so it doesn't cause the processor to reset every time I trigger the flip motor.
Robot: Betsie - RaspberryPi controlled flipper bot with gyro stablisation - too clever for her own good?

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Re: Team Antiquarian build diary

Post by Andrew_Hibberd » Tue Dec 11, 2018 3:35 pm

Hi Stuart

I really like the tapped 4mm polycarbonate, defiantly a robust method for making an antweight.

It looks like the two holes are for a jumper/switch for the receiver BEC. If you were to cut the trace between the holes and solder a 2 pin jumper you could use this jumper to select if you want to power the RX using the 5V regulator (or not).
TEAM GEEK!

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LiPO Bargain

Post by MySolderIsOlder » Tue Dec 18, 2018 12:19 pm

I realise this will be out of date very soon - but if anyone needs some more LiPOs, HobbyKing currently have both the 2S and the 3S Turnigy Nanotech 180mah in the 'bargains bin' at £3.96 for a pack of five (less than a quarter the normal price).

I went on there just now, planning to buy a single 3S (to see if those 2S/3S ESCs could handle it) so it was a pleasant surprise!

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