HardWired II

[GlenR]

Yeah wheel placement is tricky. Not only do you have to consider weight distribution but how the robot will react when it starts tilting over. Something like the drawing might pitch forwards and fall on its nose cause its quite short in length, but couldn't really say. They drive great (until the blade is going too fast to turn ) with the wheels just behind the axle but obviously no invertibility then. On the other hand having the wheels jut out the back compromises the frame strength quite a bit. Damned compromises

Having some blocks or something the robot can squat down on is pretty much essential, though most already have something like that in the form of a wedge etc.

Demon is 6mm too and yes its super high brinell steel. You have to take care welding the high hardness steels as they will crack easily due to the high carbon content. Gotta use stainless filler and Tig it else it will absolutely hydrogen crack everywhere. That and you aren't supposed to tack weld it either due to the rapid heating and cooling. Makes things tricky!

[overkill]

I'm not sure foam wheels would work on a bot that gyros; as the bot tips to one side, that wheel will take all the bot's weight on it's outside edge. A foam wheel would probably distort and crush, letting the frame bottom out earlier. Perhaps this explains what I' thinking:



You would probably be better off using a harder wheel with a wide tread like the fat Colsons that Mouldy has just put on 720. They have a large contact and won't distort. The other point here is that keeping the wheels as close to to the side walls as possible lets you keep some control as the bot tilts and also helps driving off wedges.

This video of Inertia XL perfectly demonstrates several of these problems:

Because the wheels are at the back and far behind the centre of gravity, they don't have much weight over them and that reduces their traction so Inertia can't drive the wedge under Tilley very well. When Inertial turns fast, the wheels lift off the floor very early. That's because the bot is pivoting over a line between the front corner of the wedge and the front corner of the frame, like this:



Right at the end of the match, Inertia props itself on the arena and the wheel placement doesn't help it drive off the wall - it looks like the lower wheel is off the floor due to the tapered front end.

[teamshock]

Now I've got a couple of minutes spare I can offer what I have learnt after running Inertia XL for a few years

The 2013 version that keeps being mentioned was by far the worst of the ones that I have built. I tried to make it too powerful for its own good and as a result found loads of issues with it. The first one being that to fit the Sidewinder in to drive it (was the only speedo we had at the time that could handle 8s) I had the move the entire disc mechanism forward by around 30mm which meant that the wheels were too far back. That, coupled by the switch to the A123 batteries meant that there was no weight over the wheels. The original one had 1.5kgs of Mi-Mhs at the rear to keep it level. This is why the old one had the big boxy back end. Also the change in design did allow it to drive upside down should the disc stop working.



In the video that Nick linked to above there was only one wheel working fully as one was completely loose. When this was fixed the drive was significantly better which can be shown in the two fights with Tormenta 2 from later on in that event.

Also the HDPE bulkheads worked very well and I still have both sets intact and could be used again. The black ones fom the 2013 spec had bearings fitted and worked perfectly even with the 10mm HDPE base as it meant that there was enough flex to absorb big impacts without permantly distorting.

That being said for the latest version I am switching to the 15mm Aluminium bulkheads and moving to a different design with 4WD. The front wheels are in line with the disc to hopefully give good control. Now that I have a reliable source of income it may make an appearance in some whitboards next year as I've got the inclination to finish it at last.

Hopefully this makes some sort of sense as I didn't really plan what I was going to write first

[Ellis]

the drive was significantly better which can be shown in the two fights with Tormenta 2 from later on in that event

Yes, much to my dismay! Secret plan all along methinks.

(you can continue with the topic now)

[Flag Captured]

Thanks for all the input as always!

That worries me a little then if Demon's 6mm haha - I'm not sure how the stuff you use stacks up to Hardox, Glen, but I'm not sure I'd like to try 3.2mm knowing that! Maybe 5mm Hardox could work, maybe... My main worry is that I'm aiming for essentially a 4kg bar, at 7000rpm+ with probably quite sizeable bite - that'll put A LOT of force on the whole machine, and whilst I'm going for a static shaft, I definitely don't want the whole thing twisting after one hit! That said, I don't want to make the whole thing so shock absorbant that I end up losing a lot of the power out of the bar - I'm not entirely sure that's how it works but I'm sure I'd lose some of that energy, right?

I haven't entirely written out anything though, I did think about 20mm HDPE for bulkheads at one point and they are still on the cards if they'd work better! It all depends really. I'm starting nothing on the build until I've got the plans sorted!

Hmm, I see where you're coming from there Nick, my way of looking at it was softer foam wheels - more wheel on the ground when it gyros, but I can see that being a much better benefit! I'm hoping to stick a bearing in that outer side, so might end up with 10mm between the wheel an the outer edge, might be alright...

Thanks too Will, Inertia was one of the ones I was looking at for design ideas! The weight distribution is definitely something I'm aware of now - I learned the hard way with HardWired 2 I think haha! I'm trying to build Arch so that everything is pretty much in line with the drive so there's plenty of weight around it (will probably help control the gyro-ing too) but the bar placement is something that's being quite changeable and I'm really trying to get right - at the minute I think it might actually be a little too close into the rest of the machine...

Again, the size and weight of the bar is something that concerns me - I know it's utter overkill, but I'd rather aim high with it all, create something that'll cause carnage haha.

Something I will ask though - is there a calculation that can be use to determine say, what thickness of material you'd need to use for a set of bulkheads, or is it more just trying it out and seeing how it gets on?

Thanks again for all the help too (and apologies if any of this is horribly worded, I'm very tired haha)

[overkill]

[QUOTE=Flag Captured;453426]

I'm not sure how the stuff you use stacks up to Hardox, Glen, but I'm not sure I'd like to try 3.2mm knowing that!

After bashing away at Demon for years with hardly any dents to show for it, the steel must be the hardest known to mankind! Given the weight of the weapon, motor and batteries to drive it, I think you are stuck with 3.2mm Hardox. Its not all bad though, you can use clever design to make the frame stronger.

I don't want to make the whole thing so shock absorbent that I end up losing a lot of the power out of the bar

Its actually the other way around. If you make the frame really stiff in the vertical direction, virtually all the energy will go into the opponent. If the bot runs on skid pads at the front, place them right under the weapon support columns and the path of the impact force will look like this:



As long nothing along that path bends, the other bot will be heading into orbit .

I'm hoping to stick a bearing in that outer side, so might end up with 10mm between the wheel an the outer edge, might be alright...

That should be fine; if not, you can always increase the floor clearance a little to compensate.

Something I will ask though - is there a calculation that can be use to determine say, what thickness of material you'd need to use for a set of bulkheads, or is it more just trying it out and seeing how it gets on?

Top-end CAD programs have a feature called Finite Element Analysis (FEA) that can analyse stresses and predict how much parts will bend or break. You can then tweak the design and rerun the FEA until you are happy (or bored )

[Flag Captured]

It could well be the case I'm stuck with it! Though when I've got it all sketched up properly (I am actually doing that, just hideously slowly and keep having to start over haha) I'll do some calculations on the weight and figure out what I've got left. I'm not entirely averse to using brushless drive if it proves a lot lighter, but for now I'm just sticking with brushed - bridge I can cross when I get to it, and all! If I've got enough weight left for 5mm hardox or something, then I'll be sorted, if not then clever designs will have to come out - I'd rather just have thicker armour because clever design work is not a strong point of mine, see Balsa Steel and HardWired 1 haha

Up to now, it's looking like the main body will be about 6-700mm wide which is probably an awful lot but it should help keep it stable enough... It'll probably be about 250-300mm long too, but these are just ballpark figures for now. Might actually try and cardboard my parts list up sometime and set it all out, see if I can get it all arranged passably!


Ahh yeah, I see the logic there! My worry was making it too solid that it bends, if you get me - hence adding a bit of shock absorbing stuff in it, hopefully a static shaft with 3mm wall box section bulkheads (totally not an idea borrowed from Demon) will be strong enough though. Failing that, I'll go 5mm wall!

Yeah, I've seen that used before - problem being I can't CAD haha! It's handy to note though, would be very useful to determine what I need to do to stop it from imploding on impact! The phrase 'biting off more than I can chew' definitely springs to mind here, but if it works I reckon it'll be pretty scary! Or at least, I hope it will be anyway...

Another thing I've amended is that the bar will now be just a standard one with heavy teeth as opposed to single tooth, for now at least - I feel it might work just that little bit better in terms of having the weight at the end of the bar for more kinetic energy (?)

[Flag Captured]

Another question actually, is there a formula for working out what power/speed motor I'd need to spin this bar up to a given RPM or is it just rough estimation?

[daveimi]

Roughly how expensive do you reckon this would end up being?

[Flag Captured]

Counting the inevitable enormous muck-up that results in me having to build it again from scratch?

A lot. Most of that will go into batteries and having the bar cut I reckon. The hardox for the main body won't be too expensive I'd imagine and the bulkheads are just mild steel box section which shouldn't be too expensive either. It'll definitely cost more than HardWired 2 did, but as of now I really don't know given that I haven't finalised the parts yet...

[maddox10]

With the build of Caliope and Valkiri 2 in mind, I guess £500 , with all the parts new, is realistic.

[overkill]

Don't forget that huge weapon motor & ESC!

[Flag Captured]

That might be a reasonable estimate Mario, just might have to add an extra £100 or so maybe considering I'll have to have it welded up for me and all that!

The weapon motor and ESC are both something I'm still looking at though haha, can't seem to be able to find anything suitable enough to get it up to 7000... An NTM 50-60 may do the job but I'm worried with it being a 4kg bar with all the weight at the tips. I may have bitten off way more than I can chew, in all honesty...

I mean, if it comes to it I'll stick in one of those ludicrous Scorpion motors and a 12s pack, but I want to be able to save as much weight for structure as possible because I'll need it! Also money, the scorpion ones are a little out of my budget due to recent developments in just general life haha

I'd like to say an NTM on 6s would mean I could keep everything relatively cheap and simple (still go dual packs for the drive voltage at maybe 4s, no getting round that I think) but I don't know if it'd be up to the task. People have told me before that the NTMs are torquey as they get but I'm not sure how happy it would be spinning this bar up on near as damn it a 1:1 ratio!

Actually, just a thought... Maybe I'm overcooking the bar speed? Perhaps aiming for something more like 4/5000rpm would be dangerous still, given the weight and all that being towards the outer edges of the spinning mass (aiming for 1.5kg teeth of possible). I'd still like to push 7k if I can but I'm starting to think that I may be asking a lot more than is actually possible. Even more so considering my own abilities.

[Ellis]

It could be doing 1000rpm and still be "dangerous". A £30 NTM(380kv) on 6s, at 2:1, would spin this up violently. It'd be scraping 4,000rpm which is immense. 7k really is unnecessary. The biggest hit you could theoretically get is greater, yes, but if you'll forgive the (really) awful analogy it's like an African elephant and an Asain elephant. One is bigger, but they're both still elephants, ya kno.

[maddox10]

If the 50/60 NTM is not powerfull enough, and the Scorpions a tad to expensive, have a look at this one.

http://alienpowersystem.com/shop/63m...-170kv-3200wa/

@12S it runs 7500 rpm

And yes, at full speed turning will become near impossible.

Concerning drive. Defector has run with a 3S 2200mAh pack, and had juice left after a fight.
Caliope does the same, even with the failed Brushless drive.