Alas, I’m using 130 motors and the 180s are too long. Those nerf motors are a shout though, those are some ludicrous stall current numbers for a brushed motor that size. Apparently a colleague is into his nerf modding, so I’m off on the scrounge before I buy anything…
I bought some of the Out of Darts Valkyrie motors and they arrived yesterday. Straight swap for the aliexpress ones and I feel like they should perform great, except when starting out they pull more current than my little Allegro A4950E 3.5A drivers can supply and trip the internal over-current protection.
I’m going to throw my hat in the ring for the pub beetle event in May, if I get a spot I guess it’s rev2 PCB time and I’m spinning my own motor drivers. I also think the aliexpress motors might behave more acceptably at 4s (or more), but I need to do some testing as that means more current draw while switching the intended 530mAh battery for something with less capacity.
As it stands, here’s how it performs with the aliexpress motors running on 3s: https://www.youtube.com/watch?v=Y6qvmATpInE
1 Like
Turns out I’m fighting on the 25th, so basically all my time spent not at work or asleep has been robot related. Current status:
(infodump below)
Drive is mostly done. The gearboxes took a lot of fettling to get gear mesh just right (and repeatable) and the parts easy to fabricate. I switched to 6V motors and the bot now scoots about happily at a speed that’s actually fun to drive. They don’t get too warm so I don’t think they’re going to explode but I’ve put connectors on the wires anyway, because if I make it easy to service they’re guaranteed to survive, while if I hard wire them that’s just asking for a failure.
The weapon assembly needs more machining work, it’s getting a couple of bulkheads to sandwich the worm gear onto the motor shaft and handle the forces of lifting, and also to keep it from shooting into the battery pack with just the right impact to the lifter. I’m making the parts from brass because I have broken so many drills already this project I can’t even
The weapon motor tucked in there is some aliexpress weirdness (the listing literally says “we don’t know anything else, please don’t ask us about it” but I managed to find the datasheet), it’s an in-runner brushless motor that happens to fit on a gearbox from a 16mm gear motor with a little persuasion. It also has a hall effect sensor, so I can get arm position in my software for free with no extra parts. Napkin maths and trusting the datasheet say I get roughly 40kg/cm of usable torque (60ish stall) at the arm pivot while taking about half a second to rotate 90 degrees to vertical (not at the same time).
I’m slowly running out of internal space, and that was kind of the plan all along. Any space not filled with Stuff gets chunks of foam and (if possible) some low-infill TPU inserts.
Also, weight check: As pictured, 945g.
4 Likes
I love this. It’s a great combination of a minimalist design in some ways (right angles, symmetry) mixed in with some outrageous over-engineering (welded unibody and custom PCBs). The build quality is lush, great to see that welded body, and glad it’s come out fun to drive.
(On the subject of over-engineering, I kinda feel like this whole hobby is by definition over-engineering since none of us get paid for this or achieve anything other than our own satisfaction. I do boring “proper” engineering as a day job, building robots is where I do stupid unnecessary engineering just for the hell of it.)
Thanks! I was pondering the concept of over-engineering as I rushed to finish assembling my robot in the minutes before my first fight and cursing some fiddly design choices, and I think it’s when the intricacy of the design gets in the way of assembling and using the damn thing…
I actually took some days off work to finish this thing, finishing the last parts at 11am and only getting the robot assembled minutes before the first fight (I went in with only five screws out of a possible 30+, although I never intended to use every single one that’s cutting it a bit fine).
I will do a proper damage post-mortem when I’ve returned to a reality that doesn’t entirely revolve around robots, but in the mean time here’s a before and after photo:
I came into the first fight with no weapon at all - the pinion (pulled off the motor that the gearbox came with and pressed onto the little brushless one) was spinning free on the shaft, and it bit me when I ended up stuck balanced on the lifter arm leaning against the side of the box. Loss 1.
Fight 2 was possibly the most pathetic win in combat robotics. I was up against a beautiful lead screw driven crusher that I’ve already forgotten the name of. I was struggling with some drive bugs (don’t update code the night before the event, kids), so I was an easy target for a couple of good pins, but luckily he only managed to puncture the TPU wedge mounts a couple of times before his battery died. The sensible thing would have been to drive laps of the arena, but seeing him crawling forwards slowly I thought I had an easy shot for some cheeky battering ram action. What instead happened was I hit the bot slightly off centre, flipped over, and was left spinning around upside down, stuck on my too-thick lid which didn’t fit properly, next to my now totally immobilised opponent. Win 1, because he stopped moving first, just.
Fight 3 was against my pit neighbour Forkhead. I lost the ground game on the first head on collision, rode perfectly up his forks (spaced exactly the same as my wheels’ track width), and ended up cradled in the lifter for an easy suplex. Again, stuck upside down. This time I held the lid down with some screws into the bulkhead, and of course got stuck on those instead. Loss 2.
Fight 4 was a whiteboard fight, I asked for a vertical spinner with a high chance of roofing but none were available, so instead we had a four way rumble with three non-kinetics and New York Slice. This fight was for testing purposes, so I spent the whole time throwing myself into his weapon as much as possible. The noise the steel tub made both on impacts and being thrown into the walls was fantastic, and while I lost a wedge, it was only held on by 4x M3 nuts in TPU anyway (and I’d have welded in some reinforcements to tie both sides together if I hadn’t left my argon tank open all night and leaked £50 worth of gas away into the atmosphere). I made sure to reverse into the weapon a few times too, which resulted in just a couple of small scratches on the tub (right through my sticker oi). Once New York Slice ended up in the pit I turned my attention to the other bots, and somehow got a few good pins in - going to have to re-watch the fight to see how much skill was involved there. I even managed to get a few lifts in for the first time, proving that I do indeed actually have a weapon. I ended the fight with a bent axle leading to only three wheel drive, but still mobile with a mostly functional weapon (it lost home and was stuck waving around in the air but otherwise fully operational). The crowd couldn’t decide a winner for this one, so I guess everyone wins?
All in all, very happy with my performance here for my first time out. I had a mostly operational robot at the start and end of every fight, I got a feel for driving in the arena (somehow very different to my experience racing RC cars), and being at an event in general. I’m glad I got that last fight in, as going the distance against a really destructive and reliable spinner was a great confidence boost. I actually came into this event under-weight (exact number TBC), so there’s lots of future scope to make this bot even more of a tank.
Thanks to the BBB crew (and LHG) for putting on a great event, and thanks to the other builders too! While I was furiously assembling my bot for the first fight I had three or four offers of help, and some really good compliments and advice about my bot. Great vibe and I’ll be back for sure. I won’t rest until I hear this bot hit the roof.
3 Likes
Update: Weighed the bot as it went into the arena (kind of…) and it’s not even 1300g. I’ve already got some ideas on how to improve the drive and weapon that don’t require much extra weight, so I’m practically giddy at the thought of putting almost all the remaining 200g into armour and throwing it straight into the face of the nearest kinetic weapon again to see what breaks first.
Some damage photos below:
Since I’m off to the champs in October I thought I’d make another progress update on upgrades since the last event.
Weight as pictured is about 1350g. Most obvious updates are the new wedge and weapon assembly, but I’ve also upgraded the drive and have new electronics on the way. Keen eyed readers may notice that the front of the bot is now the back of the bot due to the weapon design. I think this is ultimately a benefit, as now the lifter arm protects the battery some, and the extra length helps with self righting.
I gave up on the custom weapon gearbox and used a low profile hobby servo and a linkage. It now actually works! Unfortunately I can’t find a low profile servo that will run happily on 3s, so I have to use a buck converter to step the voltage down for this one, but I have designed and ordered some retrofit 3/4s capable drive boards that I’m hoping will solve that problem. The arm is now TPU, but with a couple of lengths of piano wire pushed through as stiffeners (and to mess with overhead saws aiming for the one exposed squishy bit). I’m also going to enclose the mechanism with new bulkheads but I’m so done with drilling holes in stainless that I’m putting it off as long as possible.
The wedge now uses threaded aluminium inserts that slide into a TPU block on the front of the bot, so it’s still shock mounted but more securely than previously. Now only 2mm, but I will be welding both sides together with a brace under the bot, so it’s going to be as stout as I can manage.
Drive is now via 4x Out of Darts Valkyrie motors on 22:1 gearboxes. Despite the power limitations of the current electronics it drives really well, hitting a decent top speed well within the confines of my beetle arena sized kitchen floor and with enough torque to break traction on carpet tiles. The bevel gearbox assembly is the only part from the pub beetles iteration of this bot that hasn’t significantly changed.
New drive electronics have been ordered! Rev1 could only manage 3.5A per channel, which causes these Nerf motors to stall when loaded and the drivers to overheat after a couple of minutes driving. Rev2 can now handle 6.5A per channel, and also has an IMU in case I want to integrate the accelerometer or gyroscope into my control or logging.
Finally, a quick video of some Roomba (clone) abuse. Unfortunately the servo screws pulled out of the (already stripped) TPU after giving the roomba some aggressive tapping, but I’m really happy that I can get reliable lifts on a 2.2kg robot. I mentioned in my Champs application that I’m doing torque vectoring, I’m still figuring out the maths but you can maybe see a little bit of it in action in this video; in fast turns the inside front wheel brakes, drifting the rear out and pivoting the bot around the braked wheel. It’s all a lot to figure out because I have to figure out how to programme it and drive it at the same time!
Very happy with how it’s coming together. It’s driving well, the weapon works, and despite crashing it a lot I haven’t done much damage. Also, the new wedge really gives the bot a strong silhouette for the audience to see hitting the arena roof.
3 Likes
New PCBs are in! So far everything seems to work, zero bodge wires required and I think only one silkscreen bug. I paid extra for black solder mask - it doubled the cost to £2.50 per bare board.
After blowing up all my hobby servos seeing if they were reliable at 3s, I determined that they weren’t, so I designed a retrofit driver board with the same motor driver as the drive PCB and an attiny85. Tested and working with a deadbugged Arduino nano in place of the attiny, it, should be good up to at least 4s, but I can’t use them in the bot til I programme the attinys and I don’t seem to have a programmer to hand.
I also had some reliability and noise issues with the aliexpress gearboxes on the nerf motors. After a quick teardown I determined that there’s hardly any overlap between the output gear and its driver. On a couple of motors I’d chipped, stripped or totally cracked this driver gear in half so I had to fix it. Have I mentioned that due to my insane packaging requirements, these are the only gearboxes I can fit in this robot?
The back of the input shaft has a step down that runs inside a small bushing in the centre of the gearbox casing, so if I chuck the input shaft in a drill and give it some love with a needle file I can reduce the diameter so it’s uniform down the whole length.
Roughly 2mm worth of shims later we have full mesh, and the gearbox goes back together the way it should! These gearboxes look like they could be configured for this kind of engagement with a different gear arrangement and gearbox housing, and the shaft even looks to have a second bearing face to match on the wider part of the shoulder. I presume this is done as an intentional weak link for whoever the OEM customer for these motors was!
I also took a video of a short drive test with the new electronics. The new drivers brake when idle as opposed to coasting, and I’ve also managed to integrate the IMU into the control loop to provide gyro feedback on the steering. As a result it’s just a joy to drive, even on the tiled floor. I can stop, spin and accelerate in an extremely predictable manner, and drive sweeping, smooth, controlled drifts going until I show my housemate or turn the camera on and then I start crashing into stuff.
3 Likes
EDIT: Wall of text below, sorry. Scroll down for pictures.
Champs was a blast! I had a little midnight reverse polarity incident the night before, resulting in no spare PCB and no brand new very expensive servo. My lifter arm ended up a waggle stick, powered by a spare servo (sans electronics which I already blew up) hooked up to a blheli_s ESC flashed with some dodgy brushed firmware I found on github. While it was almost useless as an offensive weapon against anything smaller than Cormoran it did at least let me self right a few times.
The new electronics were flawless however, and I was extremely pleased with how the bot drove in the arena. The gyro mode feels really natural and responsive to drive, and plays well with my driving style. I managed to get a bunch of practice in before the event and it really paid off, while I made a couple of unforced errors the bot never felt out of control, and it always went exactly where I asked it to, even if that was straight into another bot’s weapon. Drive wise I’m pretty sure it was one of the fastest bots there, and I had enough traction to push some other bots around a bit.
The shell/armour combo I’m super happy with too, it took that stunning one-two hit from Home Improvement with just cosmetic damage, and was only a little bit bent after 40 seconds slamming face first into Propane. I’ll bend the wedge back straight and knock the burrs off with a flap disc and it’ll be good to go again.
Competition wise, not great but an improvement on the last event. I lost the first rumble in nine second, getting absolutely wiped out by Home Improvement after I accidentally drove into their weapon. My intent was to use my mobility to drive laps of them until they lifted a wheel due to weapon gyro, where I’d get underneath them and drive at the nearest wall. I neglected to remember that while they couldn’t turn too fast, they could drive just fine in a straight line. The first hit the wedge and kicked the lifter up, popping the weapon linkage off the servo, leaving me upside down. The second came in the rear and hit the corner, punting me across the arena.
Fight 2 was versus Cormoran, and I can only describe is as like fighting a football made of coathangers. We both agreed beforehand we wouldn’t go for the pit, because after our brief first fight we wanted two minutes bouncing around in the arena, and it’s what we got! I had a great time shooting around, crashing into Cormoran and getting stuck underneath and inside it while my poor lifter waggled for all it was worth. Unfortunately near the end a jammed gearbox and a bad receiver caused some mobility issues for me, but my aggression was enough for me to land a narrow split decision from the judges. That’s a win for cream first and Ivor Dewdney, sorry Tony 
While waiting for fight 2, Tony informed me that the winner of our fight would be fighting Propane. As a result, I now had to fight propane. The first 30 seconds of the fight went about as well as I’d hoped, I was pleased to see that we were pretty evenly matched on mobility, and I was even able to get to the sides once or twice. Unfortunately, I made the mistake of showing Propane my backside one too many times, and they managed to flip me and take a chunk out of my exposed weapon linkage while I was upside down. I had actually brazed two chunks of 4mm hardox next to the linkage to protect it a little, but they managed to miss both off them and hit just the plastic ball end on the linkage. While upside down I yelled “hit me!” hoping to get a few more exchanges in, but was told “no, I don’t want to break my weapon”. I’ll take that! (Would’ve made what was described as a “dull fight” in the interview less dull, oof).
I managed to squeak in one last whiteboard against Babrog, Bob Toss, and Siren. Absolute chaos, great fun. Managed to get a couple of lifts in, pushed some bots around, and ended it all as victim to an absolutely perfect suplex into the pit, RGB twinkling forlornly and “You made me look bad, and that’s not good” for the camera to see. Can I get that as a gif?
As an aside, I’m also very humbled by all the interest in and positive feedback about the robot that I had on the day, with lots of people taking pictures of it next to their bots on the ready table, and wandering over to my pit table to look inside. I usually build my dumb projects purely for my own entertainment, so it’s great to know other people think my robot is cool too!
Some photos:
Straight to corner, where three pieces of steel meet (two welded and one brazed on top). I trust my welding a little more now.
Narrowly missing the hardox…
Finally, thanks again to the BBB team for putting on another excellent event! I had a great time, and I had some spectators come and they had a great time too. Sounds like I might have converted a few more folks. Also, big shout out to Eoin for understanding the reference and hopefully introducing a few more audience members to a cinematic gem.
Now, back to CAD. The sooner I don’t finish these upgrades the sooner I can be in a mad panic trying to finish them for the next event.
3 Likes
I feel personally attacked by your past paragraph 
Great write up and glad to hear the bot performed as expected!
Don’t talk to me or my son ever again.
A couple of us at Swindon Makerspace are trying to get some tabletop plastic antweight action going, and name begat robot - meet Fatal Deviant. 60% scale Fatal Deviation with N10 motors and a 9g mini servo. I think there’s enough room inside for me to get weird with a soldering iron and magnet wire. Sneak peak on upgraded internals for the smallest big bot out there if you squint.
2 Likes
Since I’m babysitting a 10hr print for the next iteration of the robot guts it’s time to write some stuff about the updates I teased earlier. I was mostly happy with the performance of the bot at Champs, but the multi-part internal subframe ended up making wiring the bot extremely difficult, and it was a pain to iterate designs with so many different components tied together.
After people sniping my weapon linkage my main issue at champs was gearbox reliability, and I ended up stripping all my tiny bevel gears, so I stepped up from 0.5 to 0.8 module gears. It doesn’t sound like a big difference but the teeth are much bigger, stronger, and resistant to misalignment than the old ones. I designed a new minimalist gearbox housing to suit, currently prototyped in PETG but PCBway will make them in laser sintered stainless steel for £7 each, or aluminium for £6 each. A few years ago I designed and ordered a sintered stainless body for my Casio watch, and I’ve been wearing it daily ever since. If it can survive that it can survive any combat robot.
With the new gearboxes I’ve done away with the stainless steel bulkheads, so now all the components are sandwiched in a three part TPU clamshell. The PCB slots into the bottom and all the wiring sits in channels. Big fan of this design from a serviceability perspective, although I have to figure out how to retain the motors so they don’t fall out every time I turn it upside down…
I also did some cursed CAD to figure out how to optimise the weapon linkage for the best combination of leverage and throw. At Champs it could only open to about 90 degrees, but it’s now all the way up to 120. I haven’t properly tested it yet, but it’ll comfortably self right the naked chassis, and it’ll lift my 2.2kg (much abused) roomba clone with ease.
The linkage optimisation and the new TPU clamshell mean that I’ve managed to fully enclose the weapon linkage, which was the reason I lost two fights at champs. While there’s not currently any provision for mounting hardware, I plan to fit some armour over the top of the linkage to fully protect it.
Very confident in this design now. I’m under no delusions about winning anything, but I think it’s durable enough to get knocked around some more and leave me to focus on driving.