With a big vertical bar spinner you don't really need 7k, as long as you have enough energy to throw an opponent and do a bit of damage any extra energy is just going to put extra strain on your chassis. Wraith's bar is around 1.5kg, 250mm long and will spin around 3.5k and should still be dangerous.
Also just thought, an NTM 380kv can be run up to 8s, if you ran a separate lower voltage pack for your drive and then the weapon on 8s on say a 2:1 reduction you could get the bar to around 5K which given the size and weight would be insane.
Have a look at this short slow-mo compilation: http://media.madoverlord.com/Movies/...issorhands.mov
The bar is only 500mm long, weighs about 2Kg and is doing 2,100 rpm. Now imaging that as a vertical spinner transferring twice the energy into the opponent. Now imagine the speed increased to 4,000 rpm for another 4 times the energy (KE increases with the square of the speed). That's eight times more energy than shown in the clip and to stretch Ellis's analogy to breaking point, when you get stomped on by an elephant, you don't care where it came from.
It's all trade off's, you could go for a lighter bar meaning you keep the speed and can put more weight into bulkheads/armor to actually contain the thing OR have the slower speed and the same weight, you would get a similar result either way. I am all one for stupidly powerful builds, but I would go for a lighter bar and higher spin speed to put the weight into making sure this thing doesn't rip itself apart
Yeah, I may look into higher RPMs if the single tooth bar happens, but for now I reckon 4k will be plenty enough, given the mass being at the ends of the bar. Still need to work out how to fix it together and design the thing like, but I'll cross that bridge when I get to it!
Thanks for that link Mario, that looks decently powerful for this, my only concern really is the high voltage - I'd rather keep it lower voltage for now to save on the cost of speed controllers but I'll see what happens I guess. I'll get a 50-60 and try that first, they're not overly expensive and I have a use for one anyway, if that doesn't work I'll make amends and get a higher voltage, higher power motor in there!
A low capacity pack for drive too will be perfect, I'd have gone for 3ah so it's great to know I can shave even more weight off that. May well just go with a generic turnigy pack to save a bit of money too rather than something a little more fancy like I'll use for the bar (just so that it can cope with that high amp draw regularly)
I'm glad it's being referred to as being stomped on by an elephant, I know I'm along the right lines as far as weaponry goes when that comes into it haha! I do want to push the bar speed sometime in the future but with the amended bar design, in hindsight I was probably a tiny little bit optimistic with how fast it could be pushed haha
I still need to work out how much energy that thing will have at near 4000 rpm, but I'd hazard a guess it'd be pretty high considering weight distribution on it and everything. Hopefully with a nicely made set of teeth it'll tear through armour pretty nicely. Hopefully! I'm undecided as to what to use for that still, I'm thinking a 7075 aluminium bar (or maybe Grade 5 ti if I can find a cheap enough source of it) and toolox or hardened (S7/D2?) tool steel teeth, bolted on with some high tensile bolts or what have you. I'll study the designs Buzzbar, Scissorhands and NST use first!
That's made me feel a lot better about slowing the bar down too Nick haha - will be sending things flying I hope if it's got 8 times that power! I think 8s could work too Sam, but my only problem is the extra weight and cost in that extra bit of power... I will definitely look into it though once I've got it running.
I can kinda agree there Matt, but I'd rather have a heavier bar that's slower than a faster one for bite purposes... I don't know, I'll probably see how it gets on with a heavier one - might be the entirely wrong way to look at it but I guess that'll be the best way to figure it out, seeing how it gets on in testing/battle...
I think, maybe, with the weapon sussed, and that rough design being finished, I might actually not be too far off starting this thing. Just need to cardboard it up, then CAD it and see if it'll take the stresses then may be well underway! Oh, and acquire money. That's turning out to be a bit of a major hindrance at the minute...
If it helps here is the bar and motor setup from Buzzbar. It's on the to do list to get it back up and running again.
It's tons of help, thanks!
It looks like the best thing to do would be to mill in slots for the teeth to slot in to, and then bolt them to the bar itself, so it's a little stronger that just bolting them- is that about right, or have I misjudged?
As for bolts, I'm not sure what to use but whatever they are they'll be high tensile. Would like to say M8-M10 or something but I'm not sure whether that'll be enough...
At the power levels you are aiming for, just holding the teeth on to the bar with screws is not enough, the screws will likely shear off after just a few hits. The teeth need to lock into the bar to keep it securely attached; I use a T shaped lock, while NST uses a dovetail shape:
The the dovetail method is arguably more secure, while my method allows lower accuracy machining. Either way, you need to recess the screw heads to stop them being sheared off and use the largest possible size; probably a couple of M12 in this case.
Thanks - that's the word I was looking for! Yeah, I saw how the teeth fix into place with Scissorhands's bar, and that looks very secure. I might go the dovetail route if it's a little more secure, but I'll see how it goes when I get to machining it all. Or rather, having it machined or whatever - it's way out of my depth! couple of M12s sounds good too, I'll see what I can fit on there!
Rough dimensions for the bar at the minute (for reference) are 400mm x 65mm x 15mm in Ti (Grade 5) though I'm tempted to up that 15 to 20mm. According to rough weight calculations, that puts the bar at 1.75kg, then the teeth will be 95mm x 70mm x 20mm which would put the teeth at 1.04kg each roughly (not forgetting that pieces need to be machined out of those, but also bolts in there) which would leave me with a roughly 3.75kg weapon. Add bearing blocks etc, and it's actually looking a little over what I want it to be, but I could try machining the bar itself down a little, a bit like NST and Ironside's bars are (I think Last Rites uses that sort of design too, where the edges are just slightly machined down?) just to save some more weight.
Downsizing seems a good plan too, by the time I'm done, I'm looking more towards 5kg probably, which is awesome but probably wholly unnecessary haha!
Also, side note whilst I'm posting here, near final part plan has been established -Arch expenditure.png
Still on the fence with that Optipower LiPo, they're good from what I've heard... but I don't know whether I can afford that much on it!
And I've amended the design a little so that the inside supports from the previous plan I posted will be 5mm Hardox, welded to a hardox panel as a small baseplate type thing inbetween the two, as well as the back plate to hold it together, then a 30mm dead shaft bolted to the front two pieces of 3mm wall mild steel box (which are welded to these 5mm hardox 'bulkheads') to create a solid box type structure in the middle, which I'll then bolt HDPE to to form the rest of the machine. Should according to my rough guesstimations and precision engineering be a little lighter than making the lot in steel. I guess anyway, still drawing it up (I need to learn to do that properly, I've started again on it more times than I can count) but will post up how that looks ASAP because my explanations are frankly dreadful...
For the drives you could try the 30 amp BotBitz, or the German "IBF Reiner" speedo what is a "grundlich 2 motor controller".
Posting Permissions
Reply With Quote
Bookmarks