Twig Build log - jacks first beetle Vert!?

[Jack (Jack Franklin)]

So I was sat in wiper and true having just finished a badminton session staring at the sign up form for BBB New Bloods.

I had originally planned to do a P1 style front hinge but when the BBBois released their newness criteria I wouldnt be eligible to build a lifter variant due to well… frequently building lifter variants! - so I ignored the issue figuring that I’d work it out at sign ups.

Looking at the list of weapon options I considered what to build and quickly decided that I would t have enough time to do anything as complex as pneumatic, ring spinner/fbs or a crusher real justice. And I didn’t particularly want to do a servo grabber or a hammer.

So hesitantly my finger drifted towards the Vert button and seconds later I was committed.

I then promptly forgot all about it till a while later a pal was doing a CNC madness order and I new I wanted to get a CF baseplate done so a speed ran the cad to a point where I could lock in a baseplate design and that got me here:

This came together quickly in cad thanks largely to me trying to reuse existing stuff we’re sensible. It’s using Luchadors wheels and belt set up and a half arsed attempt at repurposing The Chilli Daddy’s weapon stack. Other than that it’s a tpu chassis on standoffs similar to how I built boomslang.

I then promptly forgot about it again until another pal was doing a metal order. With his deadline/cut off fast approaching I quickly threw this together:

I’m not particularly enamoured with the profile but it should work and is practical if kinda plain. 127.7mm effective diameter, about 170g 6mm hardox 500.

I then proceeded to forget about it for another week or two until the pom deadline was looming and at that point proceeded to do another round of speed cad to sort out all the underlying chassis stuff so I could get enough things fabricated to do pom.

This brought the design to roughly this point. Kinda works if a bit plain - but we can add the details later thought

So off to fabrication we went.

Inspired largely by Filos old beater Mantra I decided I wanted phat deep pocketed bulkheads - for no other reason than they look cool AF so that was the bulk of the CNC time

This girth allowed me to recess one of TCDs 4108s in one bulkhead and if I’m doing that then surely something should go in the other I thought

Ah yes and an entirely reasonable place to house a weapon esc, perfect.

I fired up the ole ender for the first time since October and surprisingly it didn’t shit itself and ran off the chassis, some pulleys and a placeholder pla disc in short order!

As it started to come together it was roughly in this kinda shape for pom

Functional and driving but a bit boring. So off to cad I went to work out the front end and armour and see how we could pull in some more style points.

Initially I tried adding some angular belt/pulley guards but then I realized that I didn’t wanna rely on tpu compliance for ground game and wanted a hinged front end.

This naturally led to me trying to combine the two but I didn’t like how much it was feeling like luchador but angular so I decided to back to separate parts

Making the belt guards into air intakes I thought looked cool and the wheel arches gave a nice sports car vibe.

Working out the front end was tricky - I started to realize that in my fragmented and rushed approach to getting things done id probably put the front wheels too far forward which has probably led to a weapon that requires pretty substantial getting under before engagement.

I considered trying to fix this but instead decided to cad more air vents to sit under the hump lid/rear wing and house my LEDs

Which I very much enjoy even if it’s a questionable bit of prioritisation…

This brought me to this point which is roughly where I’m at in the build:

Will it work? Probably, will it be any good? Who knows! It should at least drive ok so beyond that we’ll see!

I was pretty unsure of what to name it, so I ended up deep diving my childhood and suitable a pretty suitable but very obscure reference. Kudos to anyone who can guess where the name Twig came from!

[Jack (Jack Franklin)]

Occurs to me I just told a nice story about how I made some aesthetic decisions and forgot to mention pretty much anything technical about the build.

Core build is a CF base plate, printed tpu chassis, 20mm hdpe weapon bulkheads and hdpe lids.

Electronics are my usual mix of 20A littlebees for drive and 30A one for the weapon.

The weapon is driven by a 690kv 4108 using mod 2.45 hdpe gears - this is a weird size but I wanted to be able to also use my usual nylon double helical gears ala The Chilli Daddy incase they don’t work so well so I was working to a set center to center distance and this is what fitted.

The motor is actually geared up slightly - this is a pretty dubious decision but those motors usually spin TCDs 165mm blade and with the smaller diameter was needed to hit a reasonable tip speed. We’ll see how it fairs when the steel turns up

The weapon spins on an 8mm shoulder bolt and each bulkhead has a turned aluminum bearing seat bolted into it:

Drive is from a pair of 1806 rotalink conversions (because I mostly didn’t want to buy new things) which I squared the gearboxes on and clamshell clamp into the chassis

Overall from a technical perspective it’s very much a mash up of Luchador/The Chilli Daddy and Boomslang which I guess is pretty inevitable.

[T_Y (Thomas Yau)]

Love the use of the empty space in the bulkheads to keep it compact!

[Jack (Jack Franklin)]

Thanks Thomas. Unsurprisingly the gear drive and recessed motor decision was largely: “wut if TCD sideways ” - then I realised if I can fit a 4108 in an upright I could certainly fits some other stuff in the other one

It is pretty compact tho - internal width is basically weapon module + width of two rotalinks + a couple of mm for internal dividers

The lower pocket under my thumb is so I can route wires past the drive motors

[Jack (Jack Franklin)]

So yesterday was Twigs debut and it… did not go to plan.

Frustratingly, while the bot had issue, this was primarily my fault.

I only managed to get twig into the arena for a grand total of 1.5 fights yesterday. 1 being my initial three way against Stu’s horizontal Tonk and Static a large tpu side lifter and another against Rhys wonderful shell spinner (that I’m classing as half a fight because it was a pretty limp showing from both of us - soz Rhys)

In my post event teardown I’ve identified a laughable number of failure modes on my drive considering how little arena time I managed. None of which should have been a day ender - but each lead to me shredding a timing belt and of the dozen or so timing belts in my spares box, a dozen or so were the wrong size!

I thought I had tons of spares but they were all older belts from luchador MK3 so about 10-15t too long which is what ultimately stopped me from getting back into the arena​

So what were the failure modes? Turns out TPU be wibbly and pretty much all of my problems ultimately boiled down to me under estimating just how wibbly.

Failure mode 1:

Not enough wheel arch clearance: tonk sliced through my wheel arch and made a big ole flap, this hit my tire and got pulled up into the wheel arches and bound around the wheel locking it up.

Fix: more clearance and thicker geometry on next iterations of this piece. N.b: I actually cutaway significant material in the picture above after the fight to increase clearance

Failure mode 2:

wibbly drive motor mounting and cans fouling internal guards.

This occured in both fights for slightly different reasons, in the three way I think stu hit a wheel and the flex caused the belt to yank the motor and against Rhys I think it was the sudden tension change from a belt snapping, but both resulted in the drive motor shifting and the can locking up against the internal can guard.

Fix: reprinted clam shell motor clamp piece in rigid filament instead of tpu, increased internal can clearance.

Failure mode 3: drive pulley friction welding to chassis. In my fight against Rhys one of my tpu pulleys was rubbing on my chassis and the two eventually friction welded together. This was me being slapdash in reassembly mostly.

Fix: be less slapdash, but also add more recess on the chassis to make it less likely

Universal Failure: shredding timing belts.

Each time the drive locked up I would relatively consistently shred a timing belt. I run custom cutdown T5 belts, last time I made a batch I pushed this too far and made them too narrow so theye not really durable enough.

Fix: more ordered and I’m intending to make the next batch around 4.5-5 mm wide, these were closer to 3-3.5

As a result of my usual “there is a problem that needs fixing so let’s hyperfixate on it and nothing else” brain I’ve already actioned these changes and printed a fresh chassis. Also taking the opportunity to chonk up the rear end as it’s was a bit flimsy and is the only bit of exposed underlying chassis. Things are looking promising, the drive motors are super solid now and I think these changes should fix a bunch of the issues at play, once the new belts turn up I’ll finish getting it rebuilt and we’ll see.

Ok, so it was a bit shit - but was there any good bits?

In the first fight for the minute or so where the drive worked - I think twig showed some real potential. Zipping about the arena easily and agilely and generally driving really well. It delivered some pretty good hits to both opponents and stayed super planted while doing so.

Weapon seemed very reliable - which isn’t a huge suprise with it’s TCD heritage and the tpu front ends worked well.

So what’s next for twig? - I’m getting the drive worked out and I think the current batch of fixes should work, but I just don’t know when/if I’ll actually run it again as I’m not traveling for events this year, and I’m likely to run flipper luchador for BBB pub beets and applying to champs has to be with Luchador (this is the law, I dunno why, tradition I guess).

So it’ll probably just be fixed back up and put on a shelf for the foreseeable.

[Joe (Joe Brown)]

pub beets pub beets pub beets

[Jack (Jack Franklin)]

I did consider it, but I don’t have enough clearance between the gear and the opposite upright to fit a plastic setup that I’d be happy with.

Plus I’ve still yet to really push the reptar gear in luchador to it’s limits