Experience needed regarding FW Beater and Armor

[Runsler]

not really. the whole bot as seen from the side is a triangle.
the idea was to make it invertible, so no matter on what side it drives, and having a wedge as "backside", and the spinner on the (almost) vertical side of the triangle.

Now the diameter of the spinner is fixed by how high the bot is at half of that as distance to the bot.
For an angle of 45° for the wedge i got (17+r)*tan(22,5)=h
with 17cm the length of the rest of the bot including a small safety gap to the spinner, r being the radius of the spinner and h being the height of the bot at the point where the axis is.
The left side of that equation would be the overall length from tip of the wedge to the axis of the spinner.
Not included is some extra height since the wheels would of course make everything a bit higher than just the chassis. Only ways to change this would be:
use smaller internal parts (i couldn't find any) or making a sharper wedge (and the wedge-part is getting ridiculous long then, with a lot very flat, unused space on the inside, making weight for the armor much higher).

So to make the spinner scrape the ground no matter on which side i drive, i would need a value for r that gives me an x a little less than 2r would be.

(hope this works...)
https://cad.onshape.com/documents/4b...ad700dae0c2145
you should be able to see a view from one side.
the small square are gearboxes/drive motors as seen from the side (wheels would be there), the bigger rectangle are both ESCs (brushed for drive, brushless for weapon) and the battery seen from the side. then the back wall (1cm HDPE), and those lines are the outlines to where the chassis would go, depending on weapon size and position.

Maybe this could make it a bit clearer if anybody is still interested in the overall concept.
Well... seems to be a concept not working (this way) anyway.

Will likely have to swap battery/escs and drive train, put everything in a box shape and go with a normal beater or something like that. Actually, that will only make me lose the wedge and the unique look. And i'll need a new name.
But will be way easier to build and drive, and likely more effective, too.
Maybe i can come back to that when i am more experienced, technology is advanced, and i could possibly have a few ideas how i could actually pull that off. Oh, and maybe even enough money to just try it and another bot to enter if it fails^^

Still, learned a lot just from this thread, will try to put it into use when planning this new bot (won't call it another version, too much change for that). Maybe it'll be something completely different.

[Andy]

but does it need to be that high? could you not lower the whole thing with the diameter of the weapon? or you could lower the beater as much as you make the diameter smaller so it is still on the ground when up right, since when you're upside down its kind of useless anyway since you're flipping yourself

[overkill]

One thing with having a stationary axle is that the rotating part has to be much thicker around the axle; with a 20mm axle, a 25mm OD bearing and at least 15mm of beater material around that and the beater will need a 55mm thick block of material, most of which ends up as waste. The advantage of a stationary axle is that it ties opposite sides of the bot together and ensures that bearings are aligned. Drum bots almost always use stationary axles for this reason, while beaters seldom do; they rely on the strength and rigidity of the beater to provide a 'virtual axle'.

With bearings, there are not many choices to use with titanium. One possible idea is to machine & polish a short steel tube and press fit that over a solid titanium axle - that would remove the galling problem with a bronze bushing. Apart from Mario, most vertical drum and beater spinners use ball bearings very successfully.

General design: Waaay back there was a builder called Daisy Robotics, who made a series of successful bots similar to yours. they used a short, wide drum but the concept is the same. To improve resistance to side attack he cut off the front corners at 45 degrees like this:



Turning a sharp 90 deg. corner into two 45 Deg corners adds a heap on strength, even if the weapon goes the full width of the bot.

[Runsler]

That might be a possibility, just making the weapon end a bit "thinner", so the weapon would be smaller and lighter.
Maybe i could even go with less reduction then to speed that thing up a bit.
Have to do some drawings and calculate the new weight of a front end with that style and if that would help.
maybe get the weapon more to one side, so i could get the motor on the other side of it... well... long day(s) of scetching this will be.

Also good to know drums often use stationary axles, somehow that didn't get clear from most build diaries.

Somehow i am also thinking a bit more of a wide disc or short drum now, since a short beater wouldn't be much different from a bar with a long hole in it, and i'd think a more round shape could be more efficient, distributing the incoming forces better. but will have to see how the dimensions and the weight left look when i redesigned at least the front end.

Would it be a possible way to basically build two discs, also put the teeth into those, and just connect them with a (toothless) tube?
the middle part of that tube would only be for added stability and to get more weight from the inside to the outside of the weapon.

[overkill]

Having two disks with a tube or solid block is not exactly common but the idea works well. The advantage that I see is that a hefty set of bearings can be placed in the tube section, which would otherwise be wasted space. The tube can also have a pulley groove cut into it so you can place the motor in the gap between the disks. Its back to your old plan on steroids . Another advantage of a stationary axle is that you don't need space for large diameter bearings in the side walls, so the axle can be closer to the front and the weapon projects further out from the body. That helps protect your bot as your weapon is a bit more likely to contact your opponent before it gets to your armour.

From my experience in fighting vertical disks, they should be at least 12mm thick Hardox or similar steel or they can be bent by horizontal spinners. Increasing the weapon speed is much more effective than increasing it's weight. In the KE formula energy increases with the square of the speed, so doubling the RPM gets you four times the energy.

[daveimi]

Nick you have to be the single most knowledgeable person I've ever seen.

[overkill]

<blushes> Thanks ,but not true - there are heaps of other builders with deep reserves of knowledge; Mario, Ellis, Mouldy, Jamie, just to name a few. I like to think my forte is a willingness to do research and be proved wrong - just a few posts ago Mario pointed out that I am being ripped off on titanium costs.

[maddox10]

The €70/kg for titanium remark , that's a decent price for offcuts at a good supplier.
New material cut to fit the requirements , that will be a lot more, as the supplier will have problems selling the rest of the standard sized in a reasonable timeframe (from the accountants pov).

[overkill]

And of course THE most knowledgeable guy in combat robotics; Marco from team Riobotz, who literally wrote the book.

[overkill]

Mario - I am paying the equivalent of over €100 per Kg, plus shipping from the US. The local Ti price is even more and suppliers only sell full sheets. In 4 months our government is going to stick a 20% GST tax on all imports - everyone should hang on to the EU with both hands to keep costs down!