Experience needed regarding FW Beater and Armor

[Runsler]

New Pulsar looks so good...

the design is now more or less inverted to what Ellis did.
Disc in the middle, and an (aluminium?) pulley on each side of it, with a small distance (maybe just a washer, planning with 2mm here) between so the motor pulley will have some clearance to the disc, too.
Now i'd put holes into the spokes of the disc, and put bolts from one pulley through the spokes of the disc into the other pulley.
One of the reasons i want to go with four spokes, so i can use at least four (or maybe, depending on pulley size eight) bolts to hold everything together. Not the ten bolts Ellis used, but i'd hope enough. maybe i should put a smaller inner ring into that design of the disc, so i could bolt through that instead of just the spokes.

Drilling recess points won't be that big of a problem for me, i'm a dental technician and used to work with small, but really hard stuff precisely. those are seldom round, but i think that should be achievable for me.

But why is it that grub screws suck?
hard to repair/get out once damaged? not strong/reliable enough?

One more question:
Why silver steel for the shaft? Does it have any special properties, or is it just the cheapest stuff you could use without problem?


About mounting the motor:
there are 4 screws M4 to hold the motor, distance from middle of one hole to the middle of the opposite hole 25mm.
shaft is 6mm in the middle of those, but having this ringy thing at it right where it comes out of the motor.
you said i could just not have the circlip on the new shaft, but wouldn't the endbell come off then? how would that hold? Just by the pulley not getting pulled through the bearing? That feels so wrong...

[overkill]

Silver steel is a generic name for tool steel that is usually hardened and precision ground. I can't buy it in Australia so I might have the details wrong. It will be much tougher than mild steel and a precise diameter.

Almost all disks have a hub that the pulleys are bolted to rather than bolts through the spokes themselves. It doesn't have to be done like that but it helps with keeping everything aligned and strong.

[maddox10]

Silver steel shafts are , in most cases, precision ground and polished, easy to harden steel.

Not tool steel in itself, but used to make tools. It's "just" a good grade of steel. 2 kinds are common.
1.1541 and the alloyed 1.2210

This stuff is normaly sold unhardened.

The other alternative is axle steel, as used for lineair guides. 1.7225, case hardened , precicion ground and polished.

[Runsler]

Only experimented with hardening a bit while smithing, and these experiments were... well, not quiet what we expected.

But i guess it's way easier with just a short rod of steal than with those big chunks we used. (Might also help to watch a tutorial or anything before, and not just throwing hot metal into some cold water or oil^^).

Will see what i can get here and what to do with it, but should be a smaller problem if at all.

Also... i did some drawings.
All as much to scale as i can do, and original size (didn't write all the numbers there, want to keep these sketches somewhat clean and only write the weight in the parts (didn't do all the math yet, hopefully get to finish that tomorrow).

Also, the disc is a little bit smaller now, only 22,4mm ring with one about 1cm tooth and mass to counter that (drawing that by hand would have been awful, so just the ring to visualize the dimensions). So effectively 24,4mm weapon diameter. Had to reduce it a bit since i have miscalculated something, and either my wheels would have to stick out a bit too much (and be excellent spinner targets), or wouldn't touch the ground at all plus: gives me a more comfortable 5mm clearance to the "machine room" of the bot. also didn't draw the spokes to the inside, and an inner ring to get the pulleys bolted to. just seems to be fitting better here, since i have no ideas of hubs, too, and this seems pretty straight forward.
Plus i was thinking of just letting the desc end at the inner ring and only connect it to the axle by the pulleys to get more weight from the mid to the outside. But i guess that would be way too much stress to those, even more if i want them to be just Ali.

All in all: it includes more the idea of the disc than the actual disc, because i want to try and get most other things done before to calculate the weight as precise as possible and put as much as possible into the disc.
Also doesn't include any wiring, bolts or the removable link yet, since i still ahve to figure out a few things about that. Mostly what screws/bolts and how many plus where it would be best to put the link.

Mostly using HDPE in 20 or 10mm here for side Armor and some internal stuff, only the bulkheads where weapon and weapon motors as well as pulleys get mounted on are made from 10mm Ali.
Top and bottom armour might have to be titanium to stay in weight limit (3mm), which is a bit weak for a wedgy thing. Not sure yet if i could possibly upgrade to 3,2mm Hardox, have to weit for how heavy the screws and bolts are and decide then. Could be i just use 3mm Ali first, just to see how it works, and upgrade later on. Will most likely just use ali for the front part, since i don't believe that would have to withstand much. Nothing inside there to keep save, even thought about just letting that part open. But looks do count, too, and it helps at least not to get grabbed or hooked in that easy. and possibly gives a bit sturdyness to sideway forces in the front. And i could put goggly eyes on that.
As seen in side perspective, the wall between "drive unit" and "weapon part" is drawn in both parts, causing them to overlap a bit.


Rest_k.jpgFront_k.jpgSeite_k.jpg


Known possible issues:
-Driving will be really hard. i expect a lot of gyro forces. Plus the wheels are almost completely concealed, so... only really slow turning once the weapon is powered up. And the wheels are far, far away from the center of gravity. At least in that direction this bot will be anything, but not pushy. on reverse (so wedge first) it might be different, if i can get under the other bot. with the enemys weight on the wheels, too it might work.
-Due to those small wheels and a reduction of 28.4 to 1 on them, i will be very slow. So... doesn't matter gyros would make me turn slow, i am slow anyway. Not good considering the wedge, but anyway... if this actually is the biggest problem, i am happy. faster motors are one of the easiest things to change, but first need to learn how to drive at all.
-Did a mistake on the brushed ESC: it fits perfectly in the space. But only without wires. So will have to carve out "canals" for the cables from the 10mm HDPE-wall next to the ESC. not a nice thing to do, but on the other side is just a weapon motor/esc, not the actual weapon. won't need the full 10mm there anyway.
-The belts are longer than needed, so could be they might come off. but i got two of them, so it won't be as bad as for most other bots, and i'd rather have weapon motors and theirs ESCs a bit further in the back. both to save them from possible spinner-vs-spinner contacts as well as trying to get a bit more weight to the tires. If this is actually a problem, it won't be too big of a problem to move the motors further to the weapon and use shorter belts.
-if i can't make the weight for 3.2mm hardox, top/bottom armor is rather weak, considering it is also a wedge. So... no wedge-first attacks vs. other spinners. Anyway, not that big problem vs. hammers/axes/crushers, since (except for the gearboxes) most internals got a bit of air between them and the top/bottom. you'd have to punch a rather deep hole before hitting anything important, hopefully that'll save me a few times.
-still have to build an adapter to make the gearboxes connect to the top/bottom plates. If my current idea doesn't work i might have to turn the gearboxes 45°,too and bolt one side directly into the top plate, and put a small piece of HDPE at the bottom side so i can bolt gearbox and bottom into that thing. But this would make me build another way of fixing the battery/ESC, and not just shoving a sheet of 3mm lexan under the gearboxes and fix it to the wall on the other side.

Well... still, i kinda like the design, and even have a nice paintjob in mind for it if i finish in time to do it.
But would be great if you find any other possible flaws in this, i'd rather spend a few hours more thinking and drawing than wasting materials and ordering wrong things.

Oh, and do you know a good way to bend 20mm hdpe to about 45°?
would love to make the sides from one piece instead of bolting three together, but "just put it in the oven for how long and hot you feel is right and bend it" doesn't feel right.
If i had to, i will use bolts there, too... but bending would look nicer, and save some weight on bolts again i'd rather use somewhere else.

[Andy]

I think driving will be a real issue, as there will be hardly any weight over the wheels, you might find the wheels just spin and the thing hardly moves, one thing I would say you could add to fix this but not change the overall design is using pulleys from the back wheels to another set, nearer the front, either side, so youll have three wheels each side powered by the one motor each side, this way itll drive far nicer, even though it adds a bit of extra complication, room and weight.

[overkill]

I have to agree with Andy, most of the weight is over the weapon end and the wheels will not have much grip. The problem with adding belt driven wheels at the front is that you need two sets if the bot is going to drive inverted. Its not impossible but the long triangular belt path takes up extra space and adds weight. The other possibility is to try non-driven wheels at the front to reduce friction - I'm not sure if they would be effective though.

When I Google 'UK silver steel rod' some of the suppliers list hardened rod - a bit of searching will turn up what you need.

With the disk, I would definitely recommend some sort of hub,rather than just spokes that attach to the pulleys at their inner ends. without a hub, the screws will be taking a huge amount of force and might shear if you don't use a large size. With the right hub and pulley arrangement, the screws will only be subject to the force from the motors spinning up the disk. I will knock up a quick sketch of a typical arrangement later.

HDPE is a thermoplastic and can be bent when it gets hot enough. I have bent 5mm and 10mm HDPE using a specialised heat gun but 20mm might be harder.

[Runsler]

i have seen it bent, just not the process.
And since i guess hitting the right temperature as much on point as possible i hoped for someone being able to deliver some numbers for that. Need some more research, someone has to have done a youtube video of it. there is one of everything.
Else it has to be trial and error.

Would be interesting to see the hub-setup, just fear it would take up more space so i'd have to push the weapon motors further to the side armor, rearrange their escs further to the front (if that is still possible then), and have a longer axle that's easier to bend on impact.

Hm, two extra wheels each side... Only place i see where i could add those would possibly be next to the weapon motors, and push the weapon escs more to the front if needed. But that won't be possible with a weapon hub, i fear. And i really have no idea i could make that within the weight, and that would still not be as far in the front as i'd need it (in the worst case, this would make the bot almost balance on these wheels, likely to tip over when the weapon hits anything and causing it to hit the ground, too. that could give me a big jump backwards after every hit and a lot of energy put into me instead of the other bot.
Further in the front the chassis is already getting thinner, and i could hardly make the pulley move inside.

Another solution i might see here: put the wheels i have now to where battery/esc are. i could push those a tad closer together (just have to make sure the battery can't crush the esc when suddenly jerking sideways or landing on the side, and turn it around so the cables go over the esc and can't get into the wheel), switch the actual wheels for pulleys (a bit further to the outside of the bot, too), and put pulleys and wheels a bit more into the front.
Not sure how much good that would do, and if it's worth the effort... and if i could make enough space for something to mount the wheels into except for the side armor. But at least would be along the battery and having the gearboxes to put some weight on the wheels.
Also seen some issues with mounting an axle to HDPE on both sides, due to almost unrecognizable bending when screwing that stuff together, putting pressure onto the axle. But guess i could use a dead shaft there.
Wanted to make the wheels from hdpe anyway, maybe i could just use 20mm instead of 10, making 10 of it the pulley and put a bearing in the middle. should be strong enough if made from one piece, just one more thing i have to ask my friend with his lathe for. If that all fits, i could possibly make the pulleys on the gearboxes a bit bigger than the one on the wheels, too (which will have to be bigger anyway) to also get a little bit more speed. Might have to sacrifice some strength because i won't be able to screw the wall between weapon and battery to the side armor to get the needed wheel size, but i hope i've got enough supports for the bulkheads even without that. Sad thing i need that wall to mount the "ground" for esc and battery there, alse i could shorten it to just the distance of the bulkheads.

Sooo... drawing again this morning instead of "just" math. maybe i'll be able to do the math, too.

[overkill]

I don't recall the exact temperature but when you heat up white HDPE its really obvious when its hot enough - it turns glass clear like this:




At that point its very soft and can be bent quite sharply, although probably less so if its 20mm thick. If you bend the plastic before it goes clear, it will still bend but there will be a huge amount of spring back. When I wanted some accurately formed parts for a recent project I made an MDF frame to bend the HDPE around. I used a high temperature plastic welding heat gun that gets much hotter that your regular hot air guns. It wasn't turned all the way up, so a normal hot air gun might work. plastic doesn't conduct heat well, so 20mm thick HDPE might need heat applied to both sides to get it hot enough to bend.

[Runsler]

Damn, and i got black one^^

Anyway, i guess i'll have some visual guidance to do so then. if it doesn't work well, i'll just get white one.
And making a frame would definitly be needed, would try to make the angel of the frame just a tad sharper than i'd actually want it in case i con't get it hot enough on the inside and have some springback.

In other news: managed to squish ESC and battery together a bit, allowing for a wheel, a pulley and a 10mm thick mount for both right next to them, pushing the point where the wheels touch the ground about 5cm to the front of the bot and almost doubling their size. plus the pulley on the wheel being a bit smaller, i might reach a calculated top speed of about 11mph, that's good enough for me.

But got literally no clearance around the wheel/pulley, will have to carve out just enough material from wherever i have to to make it roll. (assuming a 10mm pulley here, that has to be enough for the drive.

Also finally got a name, since the one i wanted to take originally would only have fit with the double-beater-design.
New name: "Zahnfee", literally meaning "Tooth Fairy".
Representing my job as well as what it could do with this big spinner hitting your cheek^^

And beside a name, i did some math: with new drive system, i am at 8885g (including hardox top/bottom).
not included: the actual spinner blade, bolts and screws, and maybe some small electronic parts i have to change to make everything fit.
Guess that's pretty doable.

[Runsler]

Did you manage to make a sketch for that hub yet?
will start doing the side armor tomorrow, so would be good to know if i have to make a bit more place for the hub there...
Also, how does the hub actually work?
I did believe it would also put bolts on the axis and the disc, so where is the real difference between a hub and the way i wanted to do it first?
is the disc hold by the pressure of the hub on it? That's the only thing i could imagine...


And here are the new pictures of my drawings.
Made the wheels a bit more to the front and bigger, driven by 10mm wide pulleys and fitting belts. Hope that's wide enough, since i just don't have more space. even so i have no planned clearance in this and will have to carve that out of the side walls. Or just use 8mm Pulleys, but i guess that would be too thin for the drive system.

IMG_3461k.jpgIMG_3462k.jpgIMG_3463k.jpg


(Also, anybody knows why space suddenly doesn't work in this forum? had to write this in an editor and copy-paste it)

[leorcc]

test test.

Space works fine.

[overkill]

Here is a hub and disk arrangement using your dimensions from a few days ago. Its a pretty standard set-up with an extra pulley. The advantages are that the bearing is fully encased in aluminium so it can't bend or distort. Impact forces are transmitted from the disk through the hub without involving the screws, so they can be smaller.





It may look complicated, but the individual parts are fairly easy to make and only need a small lathe - I made a larger version of this on a tiny Sieg C4 model. I picked an 80mm diameter for the pulleys based on a 2:1 reduction as you can definitely get away with a lower deduction with two motors. I went with a 20mm axle as its completely encased in the hub & bearing - it would be best if the mounts are as close as possible to the disk to avoid any bending.

Edit: just noticed that I had to increase the pulley diameter to 90mm so the pulley groove and the screws didn't intersect. One idea to reduce the pulley diameter and width is to change to a micro-V pulley. A 'J' sized micro-V (also called multi ribbed) belt is only 3.8mm thick and would get the pulley diameter down to 80mm or less. With two belts you could use a very narrow 4 rib belt to make the pulleys narrower.

[Runsler]

So, just to get this right...
There is the disc, the hub, two pulleys, a few bolts and bushings.

It seems the hub and one pulley are made from one part (is there any problem with making them from two parts? guess that would be easier/cheaper), while the disc and the other pulley are placed on that hub, and then squeezed together by the bolts. Bushing into the inside of the hub, and ready to go?
So the hub basically avoids the needing of a tube-part where everything is fixed on and the bushings come in, right?

So we have two kinds of forces involved when the disc hits:

1. the disc suddenly stops, potentially sheering off the bolts when the momentum of the pulleys (and the motors) want to keep them rotating, but the disc can't. This will be countered by the clamping of the disc between the pulleys, so the force will be distributed through friction more than just the bolts in the way. (should the hub be just a tiny bit shorter than the disc is wide, so i can really tighten those together?)

2. the disc wants to go down while the enemy gets send up, potentially bending the axis.
This will be countered by the hub with the bushings sitting tight on the axis, which is as short as possible so those forces don't get much leverage.

Somehow still unsure about this, sorry... can't seem to get the hang of this concept.

Is Ali as material for all those parts okay, or should the hub be from steel?
The way i would do this would be to just get two Ali discs and an Ali tube, and throw them in the lathe to make two pulleys and one tube that should fit tightly inside the pulleys and disc as well as having bushings fit inside it. So... after all, the hub is something to hold the bushings in and distribute the second kind of forces from the disc to a wide part of the axis? (guess for that last task it should be steel, not Ali then...).


On a second similar issue:
Since i will have to use belts for the drive train now, too...
Any ideas on what would fit there?
Pulley width is an absolute maximum of 10mm, really can't fit more in there.
8mm would be better, but not sure if that is enough for any usable belt.
Also wanted to make those pulleys from HDPE, since it's lighter, i could make pulley and wheel from one 20mm thick disc, and i believe those don't have to be as sturdy as the weapon system. If just a HDPE-wheel direct driven on a gearbox works, HDPE-pulleys should be just fine, right?



A lot of possibly stupid questions, just want to make sure and not causing any avoidable problems on these important parts.

[overkill]

The tube through the disk and one of the pulleys has to be one piece; if the tube is separate then the disk and pulleys can be pushed sideways off the tube. Here is a simplified list of steps to making the hub assembly:

Buy a piece of round aluminium stock a little wider than the pulley diameter and 25 to 30mm longer than the two parts so there is something for the lathe chuck to grip. I recommend at least using 6061 alloy or 2024 if you want a really tough hub.

Face one end of the stock and turn it to the diameter of the pulleys.

Turn the first pulley (the one without the tube) on the end of the stock.

Cut the pulley off the stock and face the other side. The central hole will be cut later.

Face the remaining stock and then turn the tube section to diameter, checking to make sure its a tight fit inside the ID of the disk.

Drill and then bore out the centre of the stock for the bronze bushing. The bushing should be a press fit, so under size the hole by around .02mm.

Take the part out of the lathe and cut it roughly to length.

Put the part back in the lathe, held by the tube end and make sure it is running true.

Face the pulley end to final length and then turn the pulley profile.

Put the first pulley back in the lathe and get the face running true.

Drill & bore out the pulley so its a close sliding fit over the tube on the other part - that's all the lathe work done.

You can now use the holes in the disk as a guide to drill and tap the hub and you are all done. It sounds like a lot of work but trust me, that is the way a machine shop would tackle it. Depending on how fast your friend is on a lathe, it can be made over a weekend from start to finish.

The hub would be extremely heavy if it was made of steel, virtually all builders use aluminium. Due to the thick cross section of the parts, they will be more than strong enough. There are a couple of reasons to start with a single piece of round bar rather than two disks and a tube; as mentioned having the tube as a separate part means the pulleys and disk could be pushed sideways off the tube, even if its a press fit into one of the pulleys. Buying a tube remotely near the right dimensions will be impossible. Holding a thin disk in a lathe while you turn the entire outside diameter is a real pain! It can be done but your friend would need a large diameter expanding collet and they are expensive & rare in a home machine shop. Cost; buying a single piece of stock may actually be cheaper as the supplier will likely charge a cutting fee to chop two thin disks off a length of bar stock. You might also be able to pick up the bar stock as an off-cut on eBay.

For the drive pulleys, timing belts are the usual choice. Making the pulleys yourself isn't an option but the commercial aluminium ones are light to begin with.

[Runsler]

Okay, i guess i understood that now...
Will have to ask him then, but that sounds really doable.

Hoped for the driving pulleys from HDPE mostly because i would (now) know how to put a HDPE-Disc on the gearbox hub, and how using a lathe to make a 1cm pulley and a 1cm wheel from a 2cm disc of hdpe seemed like a solid plan

But gonna search for those pulleys now, only found steel ones yesterday. Hard to find something with the imperial thread of the gearbox here, might need to cut that.