[BW] GR-01 Build Diary

[Giles]

Decided I wasn't a huge fan of the wedge on the back. Going back to the more compact style I had before. To counter the effect of the high drum, I'm going to use reversible scoops to push opponents up into the drum.
I printed a half scale test model of the wheel assembly to test out the scoop functionality. The material is very light and rough on the sides, so its not flipping very smoothly. The final metal version would be fine I imagine.

Feel like I'm getting comfortable with the overall design now. Going to spend the next week doing a detailed cad model with all the correct holes and such, then i'll be looking to start making prototypes!

[Giles]

Ok, starting to finalise body shape design now. Will spend the weekend in CAD trying to figure out all the details.



Will be cutting out a lot of the inner wall to reduce weight. Also considering switching to an "egg beater" weapon instead of a drum, might be easier to make?

[suvv]

looks vicious only issue you might have is that anything with a low wedge will get undernieth you at the front and drive you warever they want

[overkill]

Eggbeaters are generally much easier to make - it depends what methods you use. I get beaters cut from steel plate by water jetting and then have axles turned on each end by the same company - all I have to do is draw the part and throw cash at them . To make a beater yourself is still easier than a drum but requires a mill. If you use a hardened steel like Hardox (highly recommended), you will also need carbide cutters.

Beaters have other advantages over drums:
* one piece construction - no screws or welds to break.
* Higher kinetic energy for the same weight & diameter. The beater keeps most of its weight at the perimeter for efficiency.
* More tooth bite. The beater is usually better when going head-to-head against a similar drum.

The main disadvantage is poor aerodynamics. The beater acts like a fan and requires a larger motor and battery compared to a drum.

[Max]

The main disadvantage is poor aerodynamics. The beater acts like a fan and requires a larger motor and battery compared to a drum.

I wonder if this could've solved by making 2 half drums out of say fibre glass and bolting them on to an eggbeater, effectively making it a drum but without using the drum for structural purposes. They might even let you into the drum-off!

[brandon_nichols]

You're going to have to put wedges or something on the front because I guarantee that thing is going to keep flipping over in a hit.

[overkill]

I wonder if this could've solved by making 2 half drums out of say fibre glass and bolting them on to an eggbeater, effectively making it a drum but without using the drum for structural purposes. They might even let you into the drum-off!

I already tried that and it didn't go well at all! The centrifugal force threw the drum halves off the beater, which managed to cut one half to shreds.

[Eventorizon]

A way of quantifying how aerodynamic beaters are, Conker 3 has 2 2.7Ah 6S Lipo's driving its weapon. If I floor the weapon, it goes from 0-11K RPM in under 1 second, and then will drain the batteries flat [Or more specifically to the 3.2V cut-off point built into the ESC I use] in under one minute! [Keep in mind the fights can be up to 3 minutes :P ]

That said, provided they are designed right [the first beater for C3 wasn't strong enough so it bent], they are much easier to make and probably cost less than drums [not sure on that but you use maybe 2-3 steps & less material, where as drums require more complex machining and a big billet of Alu/Ti for the body]

A point against beaters is that usually they don't tie together the front bulkheads, where as a Drum design does which makes it much stronger. Beaters are vulnerable to having their bulkheads pulled apart by horizontals for this reason where as drums are less likely.

[Mouldy]

Build it properly then unlike jamie;
https://www.youtube.com/watch?v=3sH-9KClEJA

[RogueTwoRobots]

As much as it pains me to say it, Dave is right.

The first video you linked to Alex, the shaft wasn't bolted either side of the bulkheads (namely due to time and lack of facilities), and in the second video, the shaft was bolted using M6 bolts. M6 vs NST, it's obvious who is going to come out on top
It didn't help that back then, I thought that the standard hole size prior to tapping was 0.5mm less than the thread you were going to cut, regardless of how big or how small the hole was. Got it right this year, though typically didn't face any horizontals.

It's also worth pointing out that the drum on the 2011 and 2014 versions didn't span the entire width of the bulkheads, which meant there were gaps that were perfect for NST's bar to bite into and throw the bulkheads apart (the 15mm ali came off worse in 2014 than the 16mm Nylon did in 2011) but again, this year saw the drum span the entire width, meaning that any horizontals are more likely to catch the drum rather than the bulkheads.

Moral of the story is, wait for someone else to perfect your design and then copy the living daylights out of it.

[Giles]

@Brandon - Yep, scoop on the front will be on its way soon!

@Overkill - Egg beater it is then!

More cad work today!

Figuring out the drive system. Pretty happy with it so far.



The blue parts are spacers to help add support to the framework without the need for more threaded rod/bolts.

All of the wheels will be 3D printed to include the pulleys in one single piece. I will be insetting bearings into these by pausing the print half way, inserting the bearings and then resuming the print.

The idler pulleys will be 3D printed also. Because I have complete control over their diameter with 3D printing, I will be able to adjust them to give the perfect amount of belt tension (hopefully!).

The motors are counter sunk into the alu frame and will be held in place with a 1mm or 2mm front plate.

I've changed the material of the outer wall to use HDPE and I have also cut out the majority of the material from the inner piece, making them 86 grams instead of 200!

THINGS TO DO:

Firm up the weapon bulkheads - I'll probably add a set of bolts either side of the shaft and another plastic spacer between the two walls either side.

Add scoop - Design and integrate some form of scoop. Probably a similar idea to the mini flip out ones I printed out as a test. This will help to push opponents up into the spinning weapon.

Add weapon motor mountings and belts - Need to think about how this will work. Thinking of using two o-ring style belts for it.

Housings/shock absorbers for electronics - Thinking of putting these inside a little box which is shock mounted onto the frame. Hopefully this will take some of the stress away from the electronics.

Design an egg beater style weapon - Replacing the drum design with an egg beater.

For all of the 3D printing I will be using two types of filament.
The first one is Taulman 910 Alloy. This stuff is STRONG. I'll be posting some strength tests of the stuff when the new spool arrives next week. They have some stats on the website for it here: http://www.taulman3d.com/910-features.html I'm hoping it will be a nice light yet strong alternative.
The second filament I will be using is called Ninjaflex. Its a rubbery filament that can stretch and bend. With a durometer of 85A it seems perfect for tires and shock mounting things. I'll be playing around with different uses for this stuff a lot. One idea is to make little pouches to put the ETC's/receiver inside of.

[harry hills]

You're so legit it hurts slightly. Great work fam.

[overkill]

I don't think the 3D printed wheels will last long - all the 3D printed antweights that I have seen broke after a few fights, including nylon ones printed on pro machines by Shapeways. Give it a go, but also think of a plan B just in case.

Making printed carriers for electronics works very well, I haven't had anything die from shock damage in several years.

I'm guessing that the blue spacers are plastic. Would it be possible to replace them with a custom sized aluminium nutstrip? That would save space internally and provide a much stronger attachment between the outside bulkheads and the rest of the frame.

[Shakey]

I don't know how they've been 3D printing antweights Nick but all I can say is that it's wrong if they are dying in a few hits. If you do it right they can be EXTREMELY strong. Nylon prints being some of the strongest of the lot.

[psycho_fling]

The ability of a 3D printed part to survive in a robot is down to a number of factors. Material, printing technology, the way in which the model was printed, layer thickness etc and the design of the part in the first place.

For your wheels are you making the tyres and hubs separate or in the same build? Which printer do you use btw?

Great designs