A piece of hardox 750*750*40 weights 178 kg, and with a kilo-price of hardox being around £3 you're talking up £600.
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A piece of hardox 750*750*40 weights 178 kg, and with a kilo-price of hardox being around £3 you're talking up £600.
OK, so getting some more parts in the middle should significantly decrease the per part price.Quote:
Originally Posted by maddox10
Or the other option would be to do what we did with the middle weight typhoon and either salvage or purchase a piece of metal pipe with roughly the right dimensions and weld some hardox teeth onto it.
We want to make some kind of spinner protection for our bearing system, so can probably use a lot of the middle for that.
Have you tried tapping holes?
Tapping in hardox? Haven't done it but I'm aware that the SSAB website says it's possible. Probably need some taps a bit better than a set from silverline etc.
You can drill and tap Hardox 450 with good quality HSS tools. But those well be worn out after 1 or maybe 2 uses.
Hardox 500 forget it, unless you have full hardmetal tools.
If you tap holes in the ring, you will first need to drill them to the right diameter; waterjetting won't leave a consistently round hole. Like any hard metal, the hole will need to be sized for a lower thread engagement. Saab may have some suggestions, I would guess at 50% or less to save the sap from breaking. Taps designed for hardened steel usually have cobalt and vanadium and an oxide over nitride coating. You will also need a heavy duty cutting oil.
Update: How about making a tapped steel spacer and pressing that into a hole in the ring? If you are attaching armour to both sides , then it can't pull out.
Nice idea! That sounds much easier than tapping the hardox.Quote:
Originally Posted by overkill
Here is what I have managed to do today.
Dropped to 35mm hardox, and added some 6082T6 tracks/reinforcement for the skateboard wheels to run on.
Attachment 6171
Happy to help! In the last CAD render, are the gear teeth cut into the hardox ring? I cant see how the bearings are going to run on the ring's ID if it has teeth cut into it.
Here is an alternative bearing arrangement that I'd like some feedback on:
http://www.nswrfc.org/Nick/ring_support_bearings.jpg
It uses a pair of 30205 tapered roller bearings, which are very common & cheap. They are enclosed in a stepped roller that distributes force from the ring and keeps them aligned. here are the pros & cons compared to having separate vertical & horizontal bearings
PRO:
* Half as many bearings to mount & maintain.
* The bot can have a lower over-all hight, which offsets the weight of the rollers.
* The armour above the ring can be lower, which offsets the weight of the rollers.
* The ring is much lower, which is more effective against most bots and harder for vertical spinners to damage.
* Less (or no) armour needed under the ring.
CON:
* Increased friction between the ring and the lower shoulder of the roller.
* Might be more complex to assemble.
* The rollers might increase the over-all weight unless the smaller side armour and fewer bearings & their supports offset the roller weight.
Side note on tapping Hardox/Armox... I was chatting to the Guhring guys at MACH 2016 and they told me about a different type of tap for threading very hard materials. I can't remember the name but I remember the process.
Rather than cutting the thread this tool reshapes the metal into the thread profile. As an example, for a M6 thread you drill a 5mm hole, but for this you drill a 5.5mm (Half way) and then the tap deforms the metal into a complete thread so you are never removing material in the process, just reforming it.
Also, since you are reshaping the material and not cutting it, the formed threads are much stronger than a regular threads and are harder to destroy. While the process requires more force it doesn't produce any more heat than a regular tap due to the change in surface area.
I've not bothered looking it up recently as I haven't needed to do any serious tapping but it might be useful if you find yourself needing to tap +4mm hardox with an M5 or greater thread.
The Guhring doco indicates the cold-forming taps are only recommended up to 320 Brinell hardness, so Hardox 450 is too hard for that type of tap. I have a couple of cold-forming taps but due to the extreme torque needed, I don't use them much.
That's how I know it, forming taps are suitable for ductile materials, that said for sure there are specialised forming taps which are good for hard materials...At our work machine shop we have something similar for threading in titanium, but its a machine taps, ie mounted on the milling machine not a hand taps.Quote:
Originally Posted by overkill
LOL, ductile means different things depending on if you are talking to the sales rep or the poor sucker trying to hand tap holes.
Well some good news, we think that because the ring itself is mounted behind armor and has the single tooth mounted on it, we can make the ring out of a mild steel to make tapping it possible and reduce the price.
We can then get the tooth/blade made of hardox and bolt it to the ring with a few >M12 high tensile bolts.
The ring is mounted with 2 rows of skateboard wheels at 45° that run on the aluminium tracks bolted to the top and bottom of the ring. Using the skateboard wheels helps to prevent damage to the bearings, and they are really cheap. I will post a picture once I have modelled it.
We cannot decide what to use for the armor above/below the ring though, since it is angled we can't get it made of a large piece of hardox so the only really practical options are to either machine it out of a few pieces of aluminium (we can do this ourselves so keeps the price down) or get lots of small pieces of hardox cut and bolt them on to a frame underneath (more expensive but should be stronger).
Also bear in mind that it is invertible and we want it to be identically armoured both ways up.
The top/bottom flat armor is currently planned to be 4mm hardox with 4mm 6082T6 aluminium below it. (Might drop down to 10mm 7075 aluminium if its too heavy)
Weld the teeth to the ring. Bolts WILL come loose and you will be nothing more than a harmless spinning top after one hit.
Bear in mind that the skateboard wheels run on small bearings on an 8mm shaft. Any sudden shock and those bearings will not work anymore.
Yeah we are probably going to make the holes in them bigger and put in some larger bearings. But they are cheap enough we can test it before and see if any are damaged by running the ring into a big steel plate or something. (obviously not a great test for getting hit by another spinner)Quote:
Originally Posted by typhoon_driver
Here it is with the skateboard wheels.
Attachment 6177
What hardness of wheel would you be looking at? something like 101a I'd imagine?
We currently have 4 SHR-95A for testing. We don't want them to be too hard since they need to absorb most of the shock to stop it reaching the bearings and other components.Quote:
Originally Posted by Black-Tie Knife Fight
Could it be worth looking at some of the dual hardness wheels. The idea is that the core is hard to keep things in place and the outer layer is softer for a "best of both" approach. That said, I'd imagine that there could be an issue of separation? I'm far from an expert on the matter.
Rather than threading in the steel, why not just have a blind hole through with a nylon nut on the other side? Less faffing around on the machining side.
Not sure how that is easier... tapping the mild steel should be a walk in the park compared to the hardox. I have proper spiral flute taps which you can use with a cordless drill.Quote:
Originally Posted by typhoon_driver
Attachment 6178
Update: Oh I see what you mean now. Yeah that would probably be easier.
Problem is that we are using 60 wheels, so it gets a bit expensive if you use anything but bargain basement wheels. The ones we have are these https://www.amazon.co.uk/gp/product/...?ie=UTF8&psc=1Quote:
Originally Posted by Black-Tie Knife Fight
so £1.75 per wheel. We are went way over budget with the hardox which is why we switched to mild steel.
I agree that tapping the mild steel will be easier than the hardox but easier still would be to remove the tapped hole completely and just have a blank hole with a nut and bolt. Unless there's something else I'm missing?
Oh I see what you mean now. Yeah that would probably be easier. lolQuote:
Originally Posted by typhoon_driver
Or you can just tap the lower aluminium ring to avoid having an exposed nut.
Now that the ring is mild steel, why not machine the chamfer for the skateboard wheels directly in to the ring and do away with the aluminium rings? It saves time, money and complexity, plus setting up the milling job will be almost the same.
Although its not shown in the rendering, the aluminium rings are actually multiple pieces. Which means we can do it on our small cnc 300x300mm. So we can't fit the mild steel ring into it.Quote:
Originally Posted by overkill
One thing I am a bit worried about is the removable links. Since we have a total of 30kW on weapons max current ~600A and 6kW max current ~180A on drive what would be best to use? They need to be fairly small since we are invertible.
It is a problem TBH, but remember you will never be pulling 600A all the time.
In the HW we are trying to build we have a theoretical Maximum wattage of ~15'000W and up to 400A Continuous. However we have gone for 4 XT90's, 1 per motor. The andersons were way to big for us and we are familiar with XT90's so why change. They can take the burst current of each motor and are good for the cont. rating as well.
You might need 6 or even 8 but its one of the few low profile methods available.
Edit: This was something I started to look at, designing custom links for invertable robots that could handle massive currents. I have a few ideas but testing them and making them isn't something I am able to do at the moment.
Typhoon 2 used a 1000A military grade connector that retails around the £1000 mark (probably more with inflation and brexit in the decade and a bit since). But failing something like that, your other options should handle more than enough current. If you are drawing 600A in any continuous fashion then I would expect either your fuses to pop on the lipo or your wiring to melt.
Just a bit out of our price range then... Probably going to use a bunch of XT90 then, or make our own ones that can handle it.Quote:
Originally Posted by typhoon_driver
We will be using 8awg for the connection between esc and the batteries.
The ratings on our batteries are rather silly. They are 5.4Ah 12S LiHV rated at 65-135C (350-730A). We have 2S2P for them so theoretically could sustain 700A continuous and 1460A burst at 52.2V. So the theoretical peak power is 76.2kW (102HP) lol.
Obviously those numbers are crazy and we will probably be closer to 300A for all motors.
I back Alex's P90 recommendation but make sure you rate them conservatively. I just had a motor burn-out where the motor was connected with an MT60 connector; the connector looks OK but the plastic melted internally and fused the connector together - really not what you want in a power link!
I will probably use either 2 per motor or make my own connectors with 8mm bullets and a 3d printed/milled case.Quote:
Originally Posted by overkill
Good idea - adding a printed back shell to the XT90 connectors make them muck easier to grip. I use a printed base for the connectors as well, it make mounting them so much easier.
So recovering from the shell shock of Robot Wars being in 7 weeks...
I have been working on the armor design and weapon.
Attachment 6300
I am struggling to find a way to protect the skateboard wheels that doesn't leave large areas of armor flapping in the wind.
This is the idea at the moment.
There is a 8mm aluminium plate that forms part of the chassis, we then shockmount a 5mm hardox400 plate to it and weld on pieces round the side at 45 degrees, this should form a strong shape and help to deflect any spinners that attack us before the weapon is spinning. It also helps defect any axe/hammer blows from hitting the ring and potentially bending it.
We will weld 2 10mm hardox400 teeth to the ring which are bent at 45 degrees to defeat any flippers, this plays with the angled armor to make it hard to get under us without being hit. It should also hopefully mean we hit any spinners either horizontal or vertical in a way they are not built for.
Any thoughts?
Anyone?
10mm hardox teeth will bend on the first impact. I'd thicken them up.
It's difficult to tell how you have positioned them but I'd take a look at the teeth on Typhoon 2. Two big chunky main teeth and then two smaller ground skimmers.
As far as your 5mm hardox goes, bending it around into a ring will be somewhat of a nightmare unless there is some tooling you have to hand that we aren't aware of?
With this design you have to remember that you are attempting something that has rarely been done and even then it's rarely been done well so it's experimentation as much as anything else.
The angled 5mm armour skirts would need a fancy multi-axis rolling machine or a large hydraulic press with a custom jig in order to get the cone shape. The option of welding many small tabs together to simulate the cone shape is much lower-tech but all that welding is going to destroy the heat treating. I'd go with a vertical ring; its going to be MUCH easier to fabricate.
I'm no expert on HW armour, but if 5mm hardox is just enough for featherweights, then a HW spinner is probably going to rip it to shreds, particularly if there is an unsupported edge it can catch. The best defence is the massive ring, even when it isn't spinning; I would try to keep the 5mm armour recessed behind that as much as possible so that vertical spinners can't get at it so easily.
I don't think the angled teeth will make much of a difference to other spinners. The lower tooth is going to do all the work against wedges and sloped armour - it could be very effective if it's built strong enough. How about offsetting the upper & lower teeth by 90 degrees around the ring? That may reduce warping and loss of hardness by spreading out the welding.
Thanks for the advice guys!
I will switch to a vertical ring using the material left over from the main ring 35mm. The reason for the rather flimsy armor there is to stop the ring getting mangled like The Ringmaster, although their ring wasn't hardened. I would rather a piece of armor gets mangled than the £1000 ring.
And split the teeth so we have 4 total and increase them to 35mm. We need it to be the same on both sides in the event that we get flipped and to help balance the ring. I really don't want any teeth that go straight out from the ring, since if one of those gets hit by a v. spinner it will probably bend the ring and throw us flying at the same time.
I realize this is all uncharted territory, so it's going to be really interesting what happens! Hopefully we get picked...