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

[Scottie]

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?

[Ocracoke]

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?

[Scottie]

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.

[Scottie]

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 )

[tweedermeister]

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.

[Ocracoke]

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?

[Scottie]

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!

[Scottie]

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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[Ocracoke]

Gee, it looks so neat compared to mine.

[Scottie]

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

[Shooty]

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?

[Scottie]

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!

[Scottie]

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.

[Ocracoke]

Sweet mercy that looks impregnable.

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.

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.

[Scottie]

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.