HardWired II

[mattsdragons]

One thing I have picked up on is if you can use your base just to keep the wires etc inside then you can put the weight to good use. Try and make it so the base isn't a structural point, especially on a machine that's not invertable.

Also, if you know the amount of force in a full backlash you can determine the amount of metal needed. After a few talks with people I concluded its less to do with the thickness and more to do with the fact that someone will hit your weapon side on, then can your bulkheads take it?

[overkill]

Actually, you don't always save weight by going to a lower battery pack! There are two reasons, both to do with those inflammable numbers . First, motor power in watts is determined by one of Ohm's laws; power = volts x amps. That means that if you needed a 4,000W motor, one that ran at 5S (18.5V) would draw 216A, while a motor designed for 10S (37V) would only draw 108A. In both cases, the motors have the same output and require the same amount of energy to run for three minutes.

Next, batteries store energy and its measured in watt-hours. The watt-hour capacity is calculated by voltage x amp-hours (like that last formula, with time included). That means an 18.5V, 4AH pack has the same watt-hour capacity as a 37V, 2AH pack. If the packs were both from the same manufacturer, they would probably weigh almost the same.

Putting those facts together, it means the lower voltage 4KW motor needs the same weight of batteries as the high voltage motor to run for 3 minutes - there is no weight saving in the battery itself. There are some other factors that affect the total weight and cost; the lower voltage system is drawing twice the current and requires thicker, heavier cables, connectors and removable links. Its also harder and more expensive to make a high current ESC compared to a high voltage ESC. This is why large RC plane motors are mostly low KV and high voltage - its just easier and cheaper for the manufacturers to do it that way.

The only real reason to stay with low voltage is if you want to power the drive motors off the same pack as the weapon motor. That has the simplest wiring but runs into the high current issue above. To get around that, you can run completely separate packs for the drive and weapon, or run a split voltage system where each drive motor runs off one pack while the weapon runs off both packs and twice the voltage.

Bottom line: Ohm was a mean bastard out to ruin our fun!

[overkill]

One thing I have picked up on is if you can use your base just to keep the wires etc inside then you can put the weight to good use. Try and make it so the base isn't a structural point, especially on a machine that's not invertable.

Also, if you know the amount of force in a full backlash you can determine the amount of metal needed. After a few talks with people I concluded its less to do with the thickness and more to do with the fact that someone will hit your weapon side on, then can your bulkheads take it?

Very good points! I think the best vertical disk spinners over here have quite thin bases made of mild steel. All their structural strength is in their vertical weapon arms and external armour.

[Flag Captured]

That is a worry, but the bulkheads will be bolted to each other pretty solidly and it'll have a 25-30mm dead shaft so will be rather tough! I am concerned about the bulkheads bending which is why I wanted solid ones as opposed to machined down ones... but it all depends, really. I'd like a front Hardox scoop too but HDPE back for the weight, may be my best bet to bolt it all together as best I can but I don't know whether HDPE would be best for something as structural as that... That may be an area I need to review!

Ahh, that makes a lot more sense with the batteries too, thanks Nick! I knew that higher voltage meant higher efficiency, but that explains a lot!

I would quite like to run the entire system on 6s, that would make things very easy but I'd worry of course about the capacity... What I might do is build it to be solid enough and then see how much capacity of LiPo I'd be able to fit in... I've looked on Hobbyking and there's a 8000mah 6S Turnigy nanotech battery that ends up at about 1.1kg which is a lot, though I'm sure I'd be able to fit something like that in at a push...

The Scorpion 50-something and 12s is still doable I reckon but I'm not sure how cost friendly that'd be, though I can always upgrade if I need to I suppose!

[overkill]

Just a crazy thought; how about running two of those SK3 motors? Much cheaper than an equivalent Scorpion motor, as long as you can squeeze in an extra ESC as well.

[Flag Captured]

That could work! I do have worries about dual brushless (timing etc) though on a belt system I reckon any problems would be lessened! Might be something to look into at the very least...

[Flag Captured]

Doing a bit more design work on what will eventually become Archangel (when I finally stop being lazy/poor and build the thing)

Main thing I'm looking at at the minute though are the bulkheads - what would people suggest for these? Initially I had pocketed Alumec in mind, but because I may have underestimated the cost of materials I'm going for 6082 to keep just the general expense down.

Long story short, what sort of thickness should I go for, and what should I do in terms of machining them down? I had 20mm solid bulkheads in mind, but that will be insanely heavy I'd imagine. The main worry is them not taking the force of the bar in case of a 'perfect' hit... They'll be supported at the back by way of an equally thick panel bolting to them both, I'll get a diagram of what I mean if needs be, but it'll probably look a lot closer to Electric Boogaloo's design for reference.

[overkill]

Any particular reason for using aluminium rather than steel? You can likely SAVE weight and definitely money with the right design

[Flag Captured]

Well, nothing other than looking at other people's designs, really - was a little worried that steel would be too heavy too!

There was the whole thing with the design being based around the bulkheads too, making that as strong as possible and then just adding a bit of HDPE round that to shield electronics. If possible I wanted it to bolt together too so I could replace bits if needs be instead of having to angle grind it apart and replace a bit!

Truth be told, I was actually debating 25mm HDPE bulkheads but I don't think they'd be a solid enough option for a spinner of this design at least. Could be wrong though...

[overkill]

Agreed, HDPE just wouldn't be stiff enough to support the weapon! Its hard to argue against the versatility of a screwed together frame, although welding is vastly stronger. Perhaps you can combine both methods: it would make sense to weld the front armour together as you don't want opponents peeling it apart at the seams. The weapon arms could be made of welded steel subsections that bolted on to the front armour and the base using either steel weld nuts or aluminium nutstrip. On the other hand, I have been up since 2AM and may not be making any sense

If you do go with aluminium, 7075 from an off-cuts store would be fairly economical and you are not paying for all the fancy mould-making properties of Alumec. That 6082 aluminium is weldable, so rather than buying thick plate and machining half of it away, you could design a thinner walled structure with buttresses to make it stiffer. The only part that really needs to be thick IMHO is the axle support.

[Flag Captured]

Yeah, it worked well in Inertia XL but obviously didn't see the long term effects that had on the HDPE itself! That, and with how much power is in this bar, last thing I'd want is it to warp itself after a couple of hits. Problem with it too is that it'd have to be structural as well by design and I'm not sure how the lot would last!

I see, I think I get what you mean! It's a bit of a debate really, though if it's strong enough I won't really need to take it apart, I guess?

I'm starting to side away from aluminium for this one to be honest, looking at the steel bulkheads as more of an option now, after looking at how Catastrope and Demon do it, it's actually starting to sway me a lot more towards that kind of design. Nice as aluminium would be, I'm worried it'll be a little too heavy, or not strong enough by the time I've machined them down as much as I'd need...

[Flag Captured]

Precision engineering hour!

Quick design question for anyone who has experience with beefy vertical spinners, when I'm looking at wheel placement, where about should they go? As a VERY rough sketch of the planned layout (minus batteries and escs) this is the sort of thing I'm going for, bar's 400mm high, body of the machine, probably about 150mm high all the way round. That's what the wheels will roughly be anyway, so that's something to base it on...



Red = mild steel (3mm wall)
Red arrows = weld points
Blue = brushless motor (weapon, probably some NTM 5060)
Orange = drive motors/gearbox
Purple = Wheels
Black = Hardox, 3.2mm
Silver = bar, definitely not proper dimensions


Right, so here's the rest of the 20 questions haha

Should the wheels poke out of the back? I'd like to say yes for mobility reasons, but at the same time it concerns me a little that it'd ruin the structural integrity of the machine.

Would 3.2mm hardox be alright for the job? Demon runs a similar setup to this, but I believe that uses thicker steel... I'd hate to think it's too thin on that front and I'm going to end up twisting the entire chassis after one hit, if not - would 5mm be more suitable, or a higher grade even?

I've got a few welds on the robot, would it be better to weld that back plate on all 4 points, or bolt on for the support bulkhead type things running through the middle? I'd worry about over-welding it, but I don't know if the support is needed... I do have a fixed shaft for the bar though, so that might help too...

Finally, stability - would this sort of design be too top heavy to accommodate a 400mm bar? The bulkheads would reach probably something like 200-240mm tall, and let's say 430mm tall with the bar upright - whilst this sort of design would mean it's a lot wider so better for stability when turning, I don't know if it'll end up being too top heavy and knocking itself over too much...

[overkill]

The wheel placement looks fine to me; its always a bit of a compromise in vertical spinners. Placing them at the back often causes steering problems as they have less weight over them. Placing them right at the front is better for steering but means they are taking more vertical recoil when you hit something. IMHO, about the best place is just behind the centre of gravity, with a skid surface at the front to take all the impact forces. Having the wheels poke out the back makes them targets for other spinners, I'm not sure its worth it...

How come the wheels are so large? 150mm diameter wheels don't get you any advantage in a bot like this and just put more strain on the gearboxes. Most vertical disk bots I can think of use relatively small wheels to save weight.

Stability is always the weak point of vertical disk & bar spinners; its just something you have to live with. The main problem is gyro forces when the bot turns and the larger the weapon diameter, the worse it gets. You can counteract that with a wider frame but eventually you run into the weight limit. Magnetic hold-down is another option but its all or nothing; if the gyro forces overcome the magnets, the bot will flip really fast.

Its just a guess, but this design might have an extra instability problem. When bots gyro, they are usually balancing on one wheel and either a front or back corner. With your tapered front on the frame and the wheels fairly near the rear of the bot, the front corner is well behind the axis of the weapon and that might cause the bot to topple onto it's front in extreme cases. Its *just* a guess, might not happen.

Demon uses freakishly strong military grade steel and its definitely more than 3.2mm, more like 4 to 5mm. As a weight compromise, think about making internal parts in thinner steel and keeping thicker steel on the outside walls. You can also preserve the strength of thinner panels with gusset plates like I use in Mr Mangle.

[Eventorizon]

Some notes on Binky that might help...

-She only has 73mm wheels and she is still quick enough to land heavy hits when she needs to.

-The wheels are just behind the weapon axle. Means the steering is easy and predictable.

-The chassis flexes by the 4mm ground clearance letting the machine bottom out in a hit. Once that happens all force is transferred to the opponent.

Also...

-Your design lends itself to an exo-skeleton design with thicker armour to make its structure stiff. try using thinner walls with aluminium blocks bolted to them to support your weapon shaft.

-Inertia XL had its wheels so far back that it would pitch up almost onto its side in a hard turn, waggling its other wheel in the air. Try and keep the distance as short as you reasonably can to prevent the robot lifting itself to far up.

[Flag Captured]

Thanks Nick!

Yeah, it does appear to be a compromise - the reason I debated the wheels out the back was purely in case I got stuck upside down and for reversing off wedges. I might not end up needing it, but it's more just covering my bases than anything! Will certainly have outside bearing blocks for the wheels though and lots of shock mounting to try and minimise the impact on the motors. I've learned my lessons from this year!

I was looking at magnets too, but I'd rather use them to compliment an already stable-ish design than rely on them entirely - though if the drive will take it I'll definitely use it to my advantage... Might use something like 1kg either side next to each wheel just to help keep it down, but I'll see how it gets on I guess. Reason I debated larger wheels was purely to allow for better grip at speed, and also so I could get something with a bit more of a foam style tread so I could keep plenty of the tread on the floor when it's gyro-dancing, if that makes sense? I'm probably describing it badly!

Ahh, I see what you mean - would that be remedied perhaps by adding a small thin wedge or spikes on the front? I can probably amend that in the design, I got the design idea from Electric Boogaloo and a little bit of Inertia XL too (as well as Demon for the setup) and they don't seem to have many problems, though I don't think they're quite as top heavy as this!

I worried about that too, it looks ridiculously tough - I put two and two together and assumed it was thick mild steel, not sure how high grade Hardox would stack up to it (looking for some 650+ instead of the 450 that's usually used) but thicker stuff on the outside may work a lot better. That was really the reason for welding it to those two internal beams, just to keep the lot a lot more rigid, but I don't know whether that'll be enough... I'm trying to make the baseplate non-structural too where possible, though it definitely will bolt to the lot so it'll provide a little bit of support!

Edit: Thanks too Alex, completely didn't see your post there! Shows how long I take to reply D:

Binky does seem very nippy when you want it to be! I have noticed it seems to lose a bit of that speed though when the disc's at full, though that may just be my eyes...

Aluminium blocks too, how would you suggest working those? Little bit confused (it's late, my head stops working past midday!)
There will be HDPE bolted to the outside probably too, I thought I should mention - it won't be structural nor will it help out in anything but armour, but it's worth noting I guess.