Scottie Builds things some times. Eric the destructor - first beetleweight robot

Hey there Everybody,

I would like to introduce my bot, Eric the destructor. It is my first ever beetle weight robot and I intend to enter it in the university of west englands beetle weight competition in february. Ive only ever built a few ants and a couple of fleas, so hopefully my bot doesnt get to wrecked and goes home wearing the cone of shame!

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This bot is a vertical spinner and its rudementary dimensions is 290mm width, 160mm length and 114mm height. Its approximate weight is 1.409kg minus screws, esc's or weapon belt.

Erics destructing gear:
drive - sk3 2122-2100KV brushless motors meshed to d25 500rpm gearboxes (i forget the gear ratio)
wheels - fingertech 63.5mm diameter
Weapon motor - propdrive 2836 1400kv brushless
1000mAh 11.1V lipo battery
Various thicknesses of HDPE
1.2mm grade 5 titanium plate

Do we have weapons?! The blade is made out of two single tooth aluminium discs. The discs are belt driven using a pully integrated between them and should weigh 279g.

Im pretty comfortable with the design with exception to the front plates. They are made out of 1.2mm titanium. Do you think that will be thick enough for beetle weight?

Hey there, looks good. The titanium front panels sound OK but I wonder if they are anchored enough to withstand a drum spinner I wonder?

Thanks very much Ocracoke! I am tempted to attach the plates close to the blade on the other side of of the bend. Wait permitting ofcourse.

Hey there peeps, update time! I have included extra anchor points to attach the titanium plates, thanks for the suggestion Ocracoke. I have also started on the bots construction with the basic outline of all the HDPE parts have been cut.
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I have also had all the metal parts laser cut. They were cut by lasermaster and are the blade assembly with the arms that hold it, they are are all aluminium. These unfortunately do not include parts that attach all my motors to the body or the titanium front plates, these i will do by hand.
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I am pretty happy with what has been cut so far, although i haven't started to assemble them yet. The surface finish is a bit meh but it looks like i can neaten it up (the reason i am bringing that up is a surprise ;))

It looks pretty damn good for a first beetle, the one thing I'd say though is that the ali weapons will deform extremely quickly, I tend to go through a single Hardox disc per event although that is partly down to the extremely aggressive tooth profile I run. 290mm is also extremely side for a beetle, especially one running a relatively thin weapon.

Looks neater than my attempt at building a beetleweight so far, going to have to get a crack on with mine. ;) I seem to recall the name "Eric the Destructor" from the UWE event in February - are you building it for then?

Thanks for the Suggestion tweedermeister, it will be pretty difficult change my blade material now without fundamentally changing my design and i am waaay to far in building now, ill have some extra blades cut for when i use it and pray that i don't suffer catastrophic failure. In the future ill consider hardox for my blade.

And yes Ocracoke, it is for the UWE event. I hope to see you both there!

Good aye! Here is some december progress. I have now cut out all features into the HDPE and screwed them together. The metal arms that hold the blade have only been placed inside to see what it looks like, they are not attached to the body yet.
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Anything that I intend to detach, namely the top and front plates, I am using m4 bolts that screw into wood screw insets. Everything else is attached with normal 4mm wood screws.
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Gee, it looks so neat compared to mine. :D

I guarantee that I feel the same way about your bot. I think yours looks pretty neat so far. Like me, you know where all the imperfections are ;)

If you don't mind me asking, how are you planning to attach the metal mounts to the base? are you going to tap threads through them, or are you using some other method?

Hey there! I have attached the metal mounts to the base by drilling and tapping directly into the metal, shown below.

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Unfortunately i have had to drill and tap by hand, and i have the finesse of an ogre when in comes to using power tools!

Here is the latest installment of Erics saga.

I first tapped and screwed together my diy pulley attached to the blades. these are 6 holes for m3 screws. all the teeth are more or less aligned and it looks pretty good. Not bad considering i had to find the teeth dimensions on an obscure forum and with out the ability to cross check that it was correct, something i wouldnt want to do again!
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next I fitted some bearings into the blade. And what i mean by me a really mean a technician at my university as when i got them made i didnt factor in tolerances of the manufacturing process i was using. The blades were a little to tight for the bearings to fit in so i had to get them machined out on a lathe.
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I then assembled the blades by screwing everything together through those 3 holes. The other 2 holes are there for a safety pin to be inserted. Once assembled I placed them onto a titanium dead bar and placed it on the left metal arm. At this stage I also attached the weapon motor and its pulley to the same arm as well as fit the pulley belt.
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You probably spotted the front plate on the left side of the bot this had to go on in before i fitted the blade. both front plates are 1.5mm titanium.

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at this point I wanted to see what it looked like with the motors, wheels and battery inside it. None of them are screwed in yet so everything looks a bit closer than it should. I am however a bit concerned for the left most batter and the motor wires placed ontop of it. they are going to be a bit to close to those to motors for comfort so i need to find a way hold them down securely. I am open to suggestions for this.

Sweet mercy that looks impregnable.

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I am however a bit concerned for the left most batter and the motor wires placed ontop of it. they are going to be a bit to close to those to motors for comfort so i need to find a way hold them down securely.

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If there is any sideways movement, move the batteries a little closer to the centre, drill 2x M3 bolt holes, one either side of where the battery is going to be, thin HDPE plate with a hole at each end of it and then with a nut and washer, wind the nut+washer onto the plate with the battery in between that and the rear plate to sandwich it in is how I would do it.

Surprise time! I was waiting to post about it when my robot was fully operational, but i think i just do it now anyway. For me, part of making a beetle weight robot is to learn something new. I can safely say, interfacing bldc motors with gear boxes not designed for them, working with hdpe and assembling a weapon system that was not just a motor and a 20g blade has been a pretty valid experience! But i wanted something more, what could i do? Tbh there is only so many ways you can make a vertical spinner, but there are loads of ways you can make it look different aseptically. So i though perhaps i could anodise the metal bits. And that is what i am doing.

I have two types of metal on my robot, Titanium (front armour plate) and Aluminium (blade and internal structure). Both can be anodised. This post will just be about anodising Titanium as they both require slightly different processes, and i haven't started anodising my aluminium parts yet.

Preparation.

Before i anodised the titanium I wanted to polish them. I bought the plate from ebay and it had a rough finish on the surface, which was pretty ugly. Whatever surface finish you have will also be present post anodising. So i bought a buffing kit off ebay. This had aluminium and steel buffing compounds, 3 types of buffing discs for drills and some vienna lime. I couldn't find buffing compounds optimised for titanium so i just used the steel buffing compounds. buffing is pretty simple so wont document how i did it (I didnt actually document it in the first place DOH!), lots of tutorials on youtube though. Here is a side by side comparison of before buffing (below) and after (top).
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The basics

By using a weak acid electrolyte and passing a DC voltage through it via a titanium anode and aluminium cathode, An oxide layer forms on the anode. This oxide layer on the titanium is transparent, allowing light to pass through it and reflect off of the titanium surface. Some light also reflects off the top of the oxide layer. These two reflections can add constructively to make a certain colour to be more visible, making the surface of the titanium appear coloured. By varying the oxide layer thickness different colours can be produced. This is achieved by varying the DC voltage. Typical voltages are anywhere between 12V-120V. Caveat, you can only increase the voltage to produce different colours as a greater voltage creates a thicker oxide layer.

Anodising equipment

Weak acid - I used distilled vinegar for pickling. (You can use coke for this)
A plastic tub big enough for your part to be anodised and the cathode to be submerged in
some titanium wire
A DC supply (I required up to 74V)
Alumium cathode - I used some take away lasagna trays
crocodile clips and power cables
Volt meter
And importantly your titanium part, which is your anode

My requirements

I would like to have my plates coloured purple and to produce this I could use to voltages ranges, 18V or 70-74V. At 18V you get a sort of dark purple, it looked kind of washed out to me and i wanted something more vibrant. So I decided to use 74V.

my setup
I looped some titanium wire around some screw holes in my titanium armour plate. I connected the titanium wire to the positive of the voltage supply via some crocodile clip terminated wire. I connected the aluminium cathode to the negative of the supply.
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Problems

My initial setup used a 64V DC supply in conjunction with a 1Ah 11.1V Lipo battery. I didn't think about how long this would take and the process draws around 500mA initially due to the size of my plates. Yeah my battery went flat in 30 minutes. So I ended up with this really weird colour that I could never replicate, let alone understand the colours that it produced (below).
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This is was rather frustrating as you cannot re anodise it without removing the oxide layer, which I did by rebuffing the surface. I solved the voltage issue by using a variable DC-DC boost converter that could output up to 80V from a 12V supply.

Processing and end results

It took about an hour to fully anodise the surface of each plate to the colour I wanted. Initially I started at a low voltage and then turned the power off around 20V. Here is what it looked like half way through the process.
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I then increased the voltage to 74V and let the process complete. Here are some side by side comparisons from before and after anodising with pre anodising plates in rough and shiny finishes.
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and here is the end result.
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The plate on the left is the plate i had to re anodise. Its slightly greenish on the bottom, probably due to me leaving some oxide layer from the previous attempt. It also looks slightly duller due to being buffed twice and thus is more reflective.

I must say your beetle looks truly awesome! And anodising the case is the cherry on top. Never thought of attempting that - already thinking Evil K'Weevil will need an upgrade and not built him yet. I decided to fit a slow motor on weapon to avoid restrictions but could go faster and perhaps have interchangeable motors. But he is direct drive.

P.S. I have a similar vertical spinner weapon design concept for a featherweight. Be interested to see how you get on.

Thank you very much! Anodising, atleast with titanium, is pretty straight forward. Aluminium is a bit more involved and requires an unpleasant electrolyte. More on that later. And same to you about your robot. I am very much looking forward to seeing it complete! Im a bit unsure what you mean by restrictions though, perhaps i should reread the rules. But having interchangeable motors sounds like a great idea. having different types of motors should allow for greater flexibility in different situations as well as enhanced redundancy.

In theory, Shu! has interchangeable arm motors (a 67:1 and a 131:1) - I can't see why this wouldn't be allowed in the rules... unless you are talking about the rotational weapons section?

The anodising looks awesome and will look neat with the white plastic underneath, can't wait to see it at the Beetle Brawl. ;)

Thanks Ocracoke! All the electronics are now assembled (welcome to the jungle?). Hopefully ill have it fully assembled by the end of the weekend so i can show it's functionality. I have some videos of the blade spinning but its doesn't quite show what i want to demonstrate.

[QUOTE]Im a bit unsure what you mean by restrictions though, perhaps i should reread the rules. But having interchangeable motors sounds like a great idea. having different types of motors should allow for greater flexibility in different situations as well as enhanced redundancy.[/QUOTE]

Yes I was thinking of the 500rpm regulation and competitions allowing spinners. But as I am noob perhaps I need to check rules.

I can't see a drill bit breaching section 11. It is unlikely(?) to weigh more than 20% of the overall weight and no drill bit (that I know of) is bigger than 500mm diameter. What you might need to consider though is rule 12.4, which says no hardened steel blades that may shatter. It has saw blades in mind (RW series 3 Pussycat) but I can see that being questioned. I'd also bear in mind 12.5 which is to do the length of commercial blades (max 20cm).

Of course, interchangability on the drill bits would work around any potential issue here, you should be OK.

I was thinking about section 11.2, 11.2.1 and 11.2.2 for Scottie.

I won't use a drill bit anymore as I could not solve the chuck/drive mass/length issue in a beetle. I probably under specified the motor in EK'W.

In beetleweights, the robots which fall under that category are nearly always approved because the arena is designed to run spinners in it.

The rules more there for live event heavyweights for example, as the EO needs to check the robots competing against the class of arena they currently have. Similarly its to give warning to EOs incase someones doing something silly - like a 400 mph tip speed ect.

Ah that makes sense. Deathly hallows you scared me enough to double check the rules, seeing as I anticipate my blade to spin at around 8000rpm. Luckily I think my blade assembly will weigh just under 300g, so I doubt I'll need pre approval

This post is about some preparation for anonodising my blades. Before i attempted anodising i wanted the surface finish of these parts to be in the best condition i can make them, as any imperfections will will be visible after anodising.

Prepepatation

again I buffed them to my parts to mirror finish. As from the previous post i bought a metal buffing kit off ebay that can be used for aluminium and steel. I used a Sisal wheel with a first stage aluminium compoud (brown), then removed residue left by the the first stage with some vienna lime. then i used a stitched fabric wheel with second stage compound (blue) followed by buffing with a loose fold wheel. Buffing components are shown below:
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This is what my parts looked like pre buffing
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after first stage
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and then after second stage and buffing with a loose fabric wheel
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That last image really doesn't do my blades any justice as i was able to buff them to a mirror finish.

Anodising part two: Once I buffed my blades i moved on to anodising them. I did do some smaller parts, but due to some... unforeseen circumstances (which will be detailed in this post) i will be keeping these extra parts bare metal.

Basics and a cautionary note

Anodising aluminium is achieved by passing a direct current through an electrolyte via an aluminum anode (your part that you are anodising) and a Cathode that is as or a more noble metal than aluminium. The electrolyte is usually sulfur based solution, usually sulfuric acid and water solution. When a current is passed through the electrolyte, the oxygen is separated from the hydrogen in the water. The oxygen is deposited onto the aluminium anode and the hydrogen is deposited onto the cathode, which is gaseous and inevitably is released into the atmosphere. The oxide layer on the aluminium anode is porous and can accept dye.

Sulfuric acid, the stuff in car batteries, is highly corrosive and is commonly used as an electrolyte. Lead plates, which are more noble than aluminium and a reasonable electrical conductor are commonly used as a cathode. Lead is toxic. Many guides to anodising online describe using these. By this point anyone tempted to try anodising are probably being put off doing this. Yep i with you. I anodised my parts in my living room and there is no chance in hell am i going to use any of these in my home!

Eventually I found some guide that detail using sodium bisulfate as an electrolyte, which is partially neutralized sulfuric acid using sodium base. This stuff is used to regulate acidity in swimming pools. It is still acid but not as strong as sulfuric acid. I mixed this with some de-ionised water with a ration of 5g of sodium bisulfate to 20ml of water. I also found that using aluminium as a cathode is acceptable , no lead brain for me!

My requirements

I again would like my parts purple. To do this I repuire a purple dye. The anodising process requires a much lower voltage. I used 12V DC. The current that my anodised parts drew was around 400-700mA.

Equipment

400ml of deanodised water
100g of sodium bisulpate
three plastic tubs - one for anodising, one for washing away the electrolyte and one for the dye
purple dye - i used one made for anodised aluminium
anluminium cathode
aluminium wire
aluminium part to be anodised
Aluminium cathode - I used some takeaway lasagna trays
Crocodile clibs
volt meter
12V DC supply

My setup
I loop some aluminium wire around some holes in my part to be anodised and exposed enough wire in air to connect to a crocodile clip to which i connected to the positive of my supply. The negative of my supply was connected the aluminium backing tray cathode. Super note -> the aluminium wire must be pulled tight the anode else an oxide layer will form between them and you will loose connection to your supply.
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problems

dont use copper wire to connect your anode to your power supply. Initially I found some silvered looking stranded wire lying around. I figured its probably cheap wire so it must be made entirely of aluminium. WRONG Scottie! It was plated copper wire. and when i connected everything and turned the power on, the process immediately drew the maximum power that my supply was capable of, bypass my aluminium anode and corrode the wire at a fast pace, immediately showing me the wires true colours... traitor. This left some copper in the electrolyte and would gradually condense on the cathode. The below picture was what it looked like after i finished:
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As I said earlier you really must pull the wire tight else your part wont anodise properly. This is what happened after i "finished" one of my blades which had a poor connection:
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Also many guides suggest boiling your part afterwards. I attempted this and a few minutes the dye almost completely ran out of the metal. I tried to get more dye back into it but it was no where near as deep of a colour as what you should expect.

Processing and results

Again guides suggest to anodise for an hour. I did 1 hour and 10 minutes to be sure. You know the process is working if you find that there are some bubbles coming off the cathode and a very small amount coming off the anode:
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I then put it into a bath of water to remove the electrolyte then put it into a dye bath for 20 minutes each and here is the results:
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Here is Eric the destructor driving without armour

https://www.youtube.com/watch?v=rTYjdUa-Xko

Looks good, traction will improve in the arena and with the weight of the disc and armour. Did you figure out how to hold the batteries in at all?

The floor i was testing on is quite slippery. I have seen people talk about using liquid latex on those tyres, and i have some. So i could use that to improve traction.

fix the batteries on ill use some vhb tape, which ill stick to some thin neoprene rubber which will then be stuck to the battery. I dont intend to use the batteries for anything else and battery charging is quite easy while they are in the chassis. So ill just leave them stuck in. But in the event that I need the batteries out i can just cut the neoprene foam

Almost competition time! And with no moments to spare! I have now fully assembled my blades. After Tweedermeister suggested that my blades may deform quickly. I thought of some ways to mitigate this. I have given myself very little room to maneuver as I must satisfy a few constraints, which are significant and are:

I must attach it to a premade pulley
I must use two blades
The blades themselves must be less than or equal to 220g

With those in mind I cannot really use a full steal blades as they are to heavy and titanium is to expensive. So i resorted to making the blades out of aluminium but with titanium teeth. I also made a couple of spares just in case. The teeth were made out of 4mm thick titanium plate. I used a pillar drill to cut the holes, then the holes were countersunk. I then cut the teeth out with a hacksaw.

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The teeth were then press fit into the blade bodies with a little bit of epoy. For extra strenth i then screwed them in with titanium screws.

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This was the last thing I had to make. All I had to do was assemble my bot.

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I think i went a little bit overboard in the weight saving. I'm not a fan of the big holes i have left in the top so i may make a new one out of thinner material. But the bot is more or less battle ready, with the exception of securing my safety link.

Looks awesome, can't wait to see it do stuff in the arena! One thing that popped into my head though, was the teeth + fixtures weight accounted for on the disc's counterbalance?

Thanks bro! hopefully it will survive atleast one round ;)

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One thing that popped into my head though, was the teeth + fixtures weight accounted for on the disc's counterbalance?

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Yes i accounted for it when in the design phase. I have recorded a full weapons test and it didnt shake itself apart. Id release the footage but I was advised by my friend, the guy who is making crabsolutely Clawful, that I was standing a bit to close while testing so I am reluctant to post it. Setting good examples and all. I'll re record tonight though.

Yeah, never be around a spinner when it is active, I would hate for a big accident to happen. Somewhere very secure and far, far away from anyone. Look forwards to the video though.

Lovely work dude!

Thank you very much Ellis. Also, here is a weapon test:

https://www.youtube.com/watch?v=L3rF2PxK65I

Dear lawd that sounds scary... Little bit of movement when stationary but nothing too drastic, looks good, can't wait to see what it'll do.

Yeah, hopefully it wont vibrate off somewhere random. I'm sure that it wont sound as intimidating on competition day, or at least as intimidating as some other bots there.

Nice work scottie. Are you planning to do a post event analysis? :)

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Nice work scottie. Are you planning to do a post event analysis? :)

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Appologies for the wait, I wanted to wait for the dust to settle and get AWS54 out of the way before I re investigated Eric.

Post event, Eric structurally intact. But there is damage to some key parts and some draw backs to my design that will make it extremely difficult to make it fighting ready in the future.

Here is a list of things that I have to address, with the foremost being the most significant to me.

Wheel motor Drive and gear box:

This is perhaps the most frustrating problem that i came up against. Basically the gears that attaches to the motorshaft of the motors that were used for the wheels kept coming off. This happened to both wheel motors. If you look back through this forum thread you will find that I used BLDC sk3 motors that were epoxyed onto 25GA 12V DC motor gearboxes. I don't think I did a good enough job of cleaning the gear and motor shaft before I epoxyed them together so that did not help me.

I know some people do something similar to this and it works well for them. However, I am not a massive fan of attaching a gear box to motor by epoxy. I really do like the idea of BLDC motors used for drive, so ill look into an alternative strategy for brushless drive

The wedge menace!:

At the beetle belt I came up against some really well designed robots! Their front wedges were made flush to the floor. Yeah i didnt do this.. I Bent some titanium plates for my front armor, which resulted in quite a gap that others could quite easily get under. My blade was also bit high up, so it offered little defense against those arena peeling robots. Next time No bending of armor plating!

Weapon drive pulley mechanism:

I used a timing belt to transmit mechanical power from motor to weapon so they were essentially coupled. The pulley connected to the motor was only attached to the motor shaft an had no other support. So any strike from my blade would produce an opposite for that would travel back to my motor, which bent my motor shaft... I had a replacement motor but the same thing happened to the other. I think next time ill use oring pulleys so that i have some slip between motor and weapon and perhaps support the motor pulley on a shaft that has support on both sides.

My weapon must have been made out of something weak like paper mache... or Radditz (tfs quotes!!):

I suppose that it might surprise some people that this was my least biggest gripe with my robot. But i did account for the softness of my aluminium blades by having 2 spare sets. Had to replace them after a fight, which was a bit annoying, but this wasn't what ended combat for me in the event. Making titanium teeth did not help as the blades bent behind them and by making the teeth by hand made the blades unbalanced. So begrudgingly i would have to make them out of steel, titanium might probably be to expensive for me..

I would say anodising them purple would be enough to counter all my woes but due to my anodising method I could not seal the dye into the surface. So any solvent or oil would take the purple dye off. I also disliked anodsing with ammonium bisulfate in my living room so i doubt ill do it again..

My thoughts and closing remarks:

Naturally I would like a robot that could drive without gearboxes breaking, not get wedged to death and have a durable weapon system. Also, I really like the duel blades and BLDC drive. But If I wanted to do all those things then I would have to considerably alter Eric, perhaps to the point where it wouldn't be the same robot anymore. So with that in mind I think I am in the unhappy position of sending Eric the destructor onto the lonely path..