Harry's Beetles

hhills · 3 March 2025 20:22

MotherLoader T34 has been cracked open for the first time in a little over a year since brawl. I was purposely not touching it primarily so I wouldn’t get distracted and talk myself into building another one of the damned things but also because I believed it to be in a working state.

My intention was to just chuck it at whiteboards even I was feeling masochistic. It turned on and moved for sure but it was sadly far from working.

Worryingly the sheer shock of the beating Andy dished out had knocked the endcaps off the motor. The brushes were just about still on the com but it was barely holding on.

Both sides! While unexpected this tells me it’s not a fluke and it will happen again. My initial instinct was to pull 5mm out of the width each side to squish the motor up against the central axe bulkheads. But I’m actually a little tight on space - especially if I make myself a little gear cover to reduce the pinch points. I think I’m going to make a little brace that retains the motor with tie rods and heat shrink/epoxy the endcap.

Naturally this wasn’t the only problem. The axe was working fine when fired but had evolved itself a 6 pointed clutch (the intermediate nylon gear) and the output gear-cum-axeshaft has a nasty split.

So yes. I tracked the axes system slop to this part of the transmission. I suspected the pins driving the 12mm RC car hexes to have sheared or just plain simple grub screws slipping but it was actually the nylon gear having enough electricity to deform and round out.

I put this down to the properties of the material not playing nicely with the thin (& therefore pliant) geometry of the gear. If the gear was larger diameter or the hex bore smaller I may have had better luck. Perhaps PLA or ABS would be good as a slip on replacement? Considering my options. It’s a relatively easy problem to solve, just a question as to how much work I wish to put in.

Forks, removed completely as they were rubbish. I’m allowing myself a new wedge in 8mm (as I need to get some for Hard Nips) and a new baseplate. I’ll be keeping as much of the chassis as I can. I think I can justify a new rear but other than that everything is kept. Wiring tidied as its not up to scratch.

IrregularJoe · 4 March 2025 11:27

Is that a standard pitch gear? I’ve had good luck buying aliexpress gears, it might be worth finding one made from brass or steel and drilling that for drive pins and grub screw(s) instead. I don’t think there’s many plastics that can deal with those forces in a gear so small. SLS nylon, maybe? I just ordered some SLS nylon gearbox housings from JLCPCB and I’m very impressed.

hhills · 4 March 2025 20:03

It is standard, I have considered trying to get a length of gear stock or making my own from delrin or aluminum. That’s quite intensive for a problem that’s not quite there yet.

To be fair for the effort of that I could probably just drop to like a 10mm hex drive and keep an FDM nylon gear. If I can help it I don’t want to put a grub screw on this sized shaft at this stage of the reduction.

PLA ST feels like the best material to try. Hard enough to not deflect. I haven’t touched modern gen SLS stuff. My only experience was SLS nylon from shapeways which feels like it would suffer immediate brittle fracture.

McMullet · 4 March 2025 21:09

I tried PLA CF for some gears recently and it seemed ok. Pretty stiff and hard compared to regular PLA. PLA-ST is tough but pretty soft, I’ve had it round out on D shafts although that was only in ants.

IrregularJoe · 4 March 2025 22:44

FWIW I’m very impressed by the JLC SLS nylon. Really good detail, well fused, and decently flexible. I have seen other similar looking and feeling nylon prints abused with hammers and the like and it’s extremely robust.

Also, my little gearbox housings were a dollar each ($7 for the stainless ones). Maybe worth chucking some on an order if you’re making one.

hhills · 5 March 2025 12:25

I can brutalize the FDM nylon with a hammer too. The strength and flexibility is what has caused it to be unsuitable for this particular part and why I’m leaning towards something stiffer. I feel like SLS nylon is more of the same.

Stainless though, that’s pretty attractive to try out as a like for like part. If you do more I’m absolutely interested in chucking a few bits in for gits and shigs.

My lowest hanging fruit has been plucked. Two ABS trinkets and some M3 hardware has gently cupped the rear of the motor.

It’s a universal cure for “the back of the motor fell off”. This fits in exactly the same pocket with the existing sizes so there is no chassis surgery required.

As mentioned in passing I’ve tidied my electronics away and just hidden them in a project box. As I no longer need these panel mount XT30’s for removable links they just got jammed onto the side so I have a neat little unit. It’s almost exactly the same size as the battery which rather does help for neatness and positioning. I do want to keep the battery opposing the axe gearing as it otherwise shifts a lot of weight onto one side of the robot.

IrregularJoe · 5 March 2025 12:48

I’d actually forgotten about the stainless parts until I posted the image, that does make more sense. I’ll shoot a message your way next time I put in an order, already discovering rev2-worthy bugs on the PCBs I ordered…

hhills · 18 March 2025 14:04

So the rear has been redrawn. I was on the fence about replacing it but I had enough improvements to make it worth it. Those with laser focused eyes and scalpel like deduction skills may have been able to tell that I have swapped to a switch over the link - though I have kept the dual power lights. The holes for mounting the lid and baseplate have had some material added to them to reduce the insert based bulging without having to rejig the back end for a thicker panel (it’s already partially overlapping with the motors which sit in a pocket) Other than that, everything else is the same with the limit switch mounting unchanged.

Baseplate slopped out of some 2mm titanium and it has beefed up the robot for sure. I now remember why I don’t bother going with metal much on my beetles as it has added a noticeable heft. I think it will even out okay as I have cut a fair amount here and there. I won’t be underweight, put it that way. I may swap it to 1.5 or 1mm if push comes to shove.

The shoulderbolts have been ditched and replaced with a little bit of 8mm tube. It’s 6mm bore so a quick ream and it’s clearance for an M6. The reason for this change is so I can remove the heads of the bolts sticking out and getting dinked by spinners. I could have recut the armour so it has a counterbore and use a shorter shoulder but that would involve buying more 10mm HDPE to recut the pannels and chuck perfectly usable ones, buy a suitable bit to put the counterbore in and 4 new shoulderbolts vs a £3 tube and cutting it to length.

The sleeves are still partially supported by the armour but don’t hold themselves in tension against it. They just get that extra bit of axial support.

Just in case I wasn’t totally clear with what I meant about any of this. Also, you can take note of the sorry state of the pulley flanges. As they are 2 part to avoid coating them in support requiring clean-up post printing one of the parts is just a flat 1.5mm disc. These bore the brunt of the assault and have pretty much all failed in the same way. I’m looking to change these to lasercut plastic sheet, HDPE would be my first choice but delrin or nylon is probably easier to source.

Certainly looking cleaner with the electronics box and the sturdier baseplate. That box will be mounted to the baseplate with a couple M3’s and there should be a little printed widget to hold the battery where it should be. I’ve rolled back the armour requirements again so I’m planning 6mm HDPE. With the healthy angle it should be enough.

With a rough draft print of the back in full view. Stringy and slightly warped but it’s helped prove a point. I’ll probably use it to cut out the wibbles on the baseplate.

hhills · 26 March 2025 20:52

You may notice popping up in the background of pictures and mentioned in passing was the reimagining of Klaus, the other other beetle. I liked the frantic little hammer saw it used to be. I redrafted it a few times trying to figure out what I wanted. One such idea was a 4 bar punching saw which lately proved very effective on a recent build on here. I would have done it half cocked so it’s probably best I abandoned that particular ship.

Not the prettiest but far from the ugliest duckling here! This chassis started life as a MotherLoader rejigging where I simplified my drive train with ex Data Breach fingetech mega-ultra-uber-sparks. Generic 24mm planetary & 1806 combination but they’re super simple and just dropped in to what I wanted to do.

I wanted to do something new and interesting so it slowly morphed into a spiritual successor to Klaus. I bought one of those amazingly cheap and rubbish handheld grinders from AliExpress for pocket change and split it out to get the saw adaptor. As they are 550 based they’re a direct fit for an 1/8" shaft which makes cheap 28mm outrunners prime candidates to directly drive the saw.

I initially wanted to use a servo for simplicities sake but I couldn’t get it to fit nicely with my criteria so I got real weird with it. This nugget is a tiny drone motor jammed onto a 22mm rotalink which then drives a worm gear and THEN a straight spur stage. I needed a lot of reduction in a small space and it actually works pretty well.

The arm has the speed controller trucked inside it for space, likewise the drive ESC’s are located in pockets on the front portion of the chassis. The gears are just RC pinions yet again because it’s so simple and cheap. They run on 5mm shafts (shoulder bolts) which in turn run on bronze bushings.

Hopefully it’s clear how it works. The centre of this robot is very busy.

That’s the saw mechanism pretty much nailed down. It didn’t change much from this point onward. I then did nothing with the design for a couple months while I had other things on my mind. I ran into a little bump in the road. I simply couldn’t produce the chassis the way I would like to.

Designing it as a single part it was a long print. Especially with the settings I run to get a nice strong print in nylon it was over 24 hours and my long suffering life partner has a long standing “no printing overnight” rule. I could pause it but it is 50/50 on it leaving a weak layer join or shifting very slightly.

The simplest solution was the best and I just chopped the chassis into three and tried to make it as seamless as possible.

It interlocks together and is retained with M3 and heat set inserts. Perhaps a little small for a beetle but the baseplate and lid will be sharing that load.

I am rather proud of the front joins. I didn’t want to lose the nice sweeping radius on the bulkheads. Not wishing to waffle you much and spam pictures of the same subjects at slightly different angles.

At this point I began the rather challenging task of wiring the blasted thing. Whoever designed it was a sadist, a moron and an all round sod. Having to grease up my grotesque sausage fingers to even have a chance of slipping in and routing things. The twin batteries was amusing to design but it’s actually very annoying to get them plugged in. I thought I gave myself a gaping cavern to run the power side but reality had other plans.

It’s all there and working though, with the Fingetech screw switch in place. It’s just two repeat AM32 escs and one BBB 20a for the weapon arm. The saw is run off a 2212 1400kv (£3.50, consumable) and a blheli 40a long 'n thin controller.

The tracks are nothing special save for being orange. Same 30a polyurethane tread with TPE core as ML but shorter. It drives extremely smoothly though is far too fast for me.

I want to get the chassis printed up for real and cut a base & lid out of carbon fibre. I planned to lasercut and fold the wedge out of aluminum or steel but I think it might just have to be 6mm HDPE I can hit with a router temple as per usual.