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

[Deathly Hallows]

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.

[Scottie]

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.

[Ocracoke]

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.

[Scottie]

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.

[Deathly Hallows]

[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.

[Ocracoke]

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.

[Deathly Hallows]

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.

[Garfie489]

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.

[Scottie]

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

[Scottie]

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:
IMG_20180127_165432.jpg

This is what my parts looked like pre buffing
IMG_20180129_193931.jpg

after first stage
IMG_20180129_205006.jpg

and then after second stage and buffing with a loose fabric wheel
IMG_20180129_215423.jpg

That last image really doesn't do my blades any justice as i was able to buff them to a mirror finish.

[Scottie]

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.
IMG_20180130_183725.jpg

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:
IMG_20180130_234906.jpg

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:
IMG_20180131_003220.jpg

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:
IMG_20180130_183850.jpg

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:
IMG_20180130_230232.jpg IMG_20180131_003200.jpg

[Scottie]

Here is Eric the destructor driving without armour

[Ocracoke]

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?

[Scottie]

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

[Scottie]

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.

IMG_20180202_164753.jpg IMG_20180202_180213.jpg

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.

IMG_20180202_183928.jpg IMG_20180202_183636.jpg

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

IMG_20180204_200341.jpg IMG_20180204_200348.jpg IMG_20180204_200403.jpg

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.