Use a single motor and ESC and otherwise ignore Dave, he doesn't know anything, go Hobbyking!
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Use a single motor and ESC and otherwise ignore Dave, he doesn't know anything, go Hobbyking!
Yeah what does Dave know about building a decent drum bot ;)
Below are some Cad drawings of the kind of thing I was thinking of.
http://i1261.photobucket.com/albums/...ew%20image.jpg
http://i1261.photobucket.com/albums/...ve%20image.jpg
http://i1261.photobucket.com/albums/...de%20image.jpg
Some stats:
-Dimensions: 360x265x80mm with 100mm wheels
- 6mm Hardox armour with 5mm sacrificial HDPE over the top
- Frame/Chassis is all aluminium, would try and get a decent grade rather than the cheap soft stuff
- 6S 60C 4000mah lipo, NTM 50-50 brushless and 100A Red Brick esc, TZ85A escs and either GR02 or RangleBox drive
Then the drum would either be 3" Aluminium billet or HDPE;
The aluminium one puts be right on the weight limit without things like wires, connectors and with just 6mm HDPE/polycarb for the lid/base, most likely I would have to pocket some of the aluminium and find other ways of losing weight.
The HDPE drum would leave me with enough weight too have 4mm Hardox for the lid and baseplate and I would still have almost a kilo left spare. The thinking is that theatrically assuming the drum is spinning nothing should ever get to the actual drum as they should be hit by the teeth first, if they do hit it then it will just take a gouge out and not send me flying, I can then easily melt more plastic into the gouge or replace the drum (each one would only cost around £12 and are easy to machine so I would carry a few spares).
So what are people's opinions? Any suggestions for improvements to the design?
Looks alright over all, you need to radius or chamfer those back corners though. Ditch the HDPE over the hardox, if you have 6mm Hardox you won't need it.
Don't use HDPE for the drum whatever you do, it will turn to a black twisted mess the moment it hits anything. Any of the good Alu grades will to: 7075, 6082, 6061, 2014. Check out 720's battle against NST and look at the hole HST made in its 7075 Alu drum! Now imagine if that was HDPE; it would probably destroy your weapon.
GR02's are no longer in production so you would either need to go Ranglebox or Banebots, either of them will do fine though the Banebots are much lighter but more costly.
All this said, Jamie, Dave and Guilherme are the people to go to for proper drumbot advice, they know their stuff.
HDPE drum? Interesting concept and I can understand the reasoning behind it, but....
The teeth may take the impacts rather than them reaching the drum, but the drum still has to be strong enough to put up with the forces that'll be going through it. Regardless of how the teeth are mounted, those forces will transfer some way or another and, over time, will probably cause deformation of the drum.
Also, can't tell from the pics (on my phone) but would you be running the belt from the brushless directly onto the drum body? If so, the HDPE isn't going to enjoy the heat generated from friction.
Looks a compact, solid design overall though.
Which corners do you mean? You mean the 90 degree foods in the armour at the back?Quote:
Originally Posted by Eventorizon
Hmm, I thought the HDPE drum would attract criticism, in some ways you think if an aluminium drum is going to get destroyed you may as well make it out of something easy/ cheap to replace! But obviously if it falls apart during the actual fight its a probes as then odds are you are not going to win the fight, just needs to be strong enough to survive so maybe aluminium would be the way to go, another option I guess would be nylon for increased rigidity but that may be too brittle and still has a lot of the issues.Quote:
Originally Posted by Eventorizon
At the moment the drum is solid material, there is no shaft going all the way through but a separate, 40mm shaft at each end so the plastic ought to be fairly rigid. This does mean I could use the aluminium and just bore a hole through the centre to save weight but ideally I want the walls to be left as thick as possible to avoid the drum getting crushed/punched through.
Perhaps a composite drum could work, metal centre to give rigidity and plastic outside or visa versa.
Yeah I realize the GR02s are out of production so would be a matter of trying to get some second hand ones, depends really on the cost of the RangleBox units which hopefully we will find out soon.Quote:
Originally Posted by Eventorizon
@Jamie: yeah the belt isn't shown but will run directly onto the drum, hadn't thought about the heating issue, didn't realize it would get that hot! And if I were to go HDPE I would have to give some thought to how the teeth where mounted, I was thinking of counterbored bolts in the teeth going all the way through to the other side then into a threaded hole in the tooth on the other side. Alternate bolt direction to keep drum balanced.
I'm by no means a drum/spinner expert but having seen some of the drums at the 2014 and '15 champs i feel i can offer something.
6mm polycarb for a lid is plenty, no axe is getting all the way through it. Having seen what the likes of LH3, No toy and Hatchet actually do to it you'd be completely safe using it. As for a base, you'd be better off with hdpe or even some 2mm ti/Alu, you could use polycarb if the base is non structural (if you've seen Hatchet's 10mm base last year you'll understand), you won't need hardox top and bottom panels, it's really a waste of money/weight.
As for your outer armour 6mm hardox is way overkill, 722 uses angled 3.2 and i believe Drumroll this year used regular steel brackets with hdpe over the top. Spinners are so powerful nowadays that a decent hit on hardox will bend it and you'll never get it straight again being 6mm, if you went down to 3.2 that would save you a huge amount of weight and wouldn't really leave you any worse for wear.
I've had some past experience using plastic drums back in the day, my first attempt used PVC a brittle plastic and was a total noob failure, it was powered by a "gold motor" and instantly cracked on first impact, lucky the end caps kept it all in one piece.
Second attempt was HDPE this proved to be much more durable, granted it only had a hand full of battles and never went up against the spinners of today but I believe it would still be a viable option if I was still building today. Only issue I came across is when little hitter got a perfect hit on the aerial cover and bent the shell into the path of the teeth, the sudden impact from the collision warped the bar and managed to pull a single bolt through the drum. That time it is was powered by a 1.5hp Ev Warrior motor, I believe a better designed bar and correct internal support for the teeth would work better. I did move onto a saw like disk around the drum but never got tested enough, it was fun lots of sparks but not designed for flipping or throwing another bot.
But these examples are from a old featherweight, modern high power and speed brushless motors would add another factor for the design of a plastic drum, I say why not try it.
ha, I remember those robots^ , thanks for making my feel old.
As supreme leader of the drum bots and current champion of champions within the drum bot community my advise is as follows;
The number 1 golden rule- Ignore everything Jamie says, every word he speaks is a lie or hard to understand because he's a dirty scott bag.
The second rule of drum club, is don't talk about drum club.
Third rule, plastic bad - metal good, even if its not up to Alex's standards, 6082 worked fine for me, it took a huge hit from NST and didn't fail, won me the fight... its how you mount your teeth that really matters... and in plastic they are always going to break out.
Final rule, don't base your robot around parts sold by Ellis- i wouldn't want his dangle-box products all over my machine.
Have fun.
Hi Mario, out of interest how do you go about connecting this type of wheel to a GR02? If I understand correctly the wheel is designed to take an M10 nut but I guess you make up some sort of custom adapter?Quote:
Originally Posted by maddox10
Also, couple of modifications made to the CAD:
http://i1261.photobucket.com/albums/...V3%20image.jpg
Main changes are at the front the very front bits are removable so if they get bent I can swap them out and could try out a couple of different shapes for the front to find what works best for getting under people to bring them up into the drum. I've also got rid of the button head bolts and replaced them with countersunk bolts going into a strip of hardox which should mean they wont pull through the HDPE but also should be caught by vertical spinners but it does leave me more vulnerable to horizontal spinners.
But what I have realized was that I had misremembered the density of steel (argh) so all my mass calculations were wrong :(
So either I have to drop the Hardox down to 4mm with just those front bolt on pieces 6mm or get rid of the HDPE, front bolt on pieces and the hardox strips for the bolts (but these wouldn't be necessary anyway as I could countersink the hardox as the HDPE wouldn't be in the way) then I should just about be able to fit in the 6mm hardox.
Which do you guys think is preferable? The big issue with the 6mm hardox is that if the front wedge bits get bent out of shape there will be very little I can do about it other than replace the entire outer armour.
Firstly, nice CAD work, you're clearly comfortable in Solidworks!
The main question mark from what I see is the strength of the drum mounting. Looks like the shaft is dead which is good, but it seems a bit skinny otherwise. You have what, based on colour, is aluminium plate mounting the drives. Traditionally these would be brought forward and the drum would mount to them, in this case there is a slim (alu?) plate going across the front, which ties into the relatively thin (hardox or otherwise) sides, which then go forwards to support the drum.
Point is I think a hit from any good horizontal will badly deform the front, either by ripping a side out away from the drum or shunting them both sideways.
It's hard to strengthen that up without making use of the wheel bulkheads (which would also need thickening depending on grade), but then you get that nobody, mouldy or something they call him, accusing you of making a 720 clone. Number one key to success is don't listen to anything he says, ever. :)
It looks like you could save a good bit of weight if you reduced the chassis height? T3's internal height is just 50mm in order to squeeze the most out of the weight limit. Perhaps you can drop the height here so you can put weight back into other areas.
Yeah I have been concerned about those front plates getting bent and thought about using the wheel bulkheads but as you say then it looks like 520 clone, here are some images without the drum to give you a better idea of how it works:
http://i1261.photobucket.com/albums/...ent%20drum.jpg
http://i1261.photobucket.com/albums/...um%20image.jpg
There is a large titanium axle at either end 40mm diameter with a 16mm hole though the middle, the drum spins on bearings on these axles then a 16mm rod made of either titanium or aluminium goes all the way through the centre, each end has an M8 tapped hole so a bolt goes from the outside of the hardox armour into these holes, the idea is that this should tie them togather so they are less likely to be pulled apart and also acts as a spacer to stop them being pushed together.
I have been thinking about making it less tall but it would mean I would have to machine down the flat bar used to make the chassis unless I can get it all the way down to 60mm as I am currently at 3" so it is quite a large step down but may be possible, could mean reducing the drum diameter as well which will mean smaller bearings and so a smaller shaft going through the middle but could save a lot of weight.
Yep, they are very vulnerable to horizontal spinners.Quote:
Originally Posted by Max
In Solidworks you can assign materials to different bodies so you don't have to do your calculations manually.
Attachment 5426
If you right click on a body, materials, edit material, then choose one from the list.
Attachment 5427
Then you can go to the Evaluate tab and then go to Mass Properties. It will break down all the body masses for you, give you the total and show you the centre of mass.
The reason I said steer away from GR02's is that their will come a point where there are no more left and suddenly your bot wont work. If something breaks you have no way of replacing it. You are best to design around a part you know is still in production and leave what remains of the GR02's to the machines that already rely on them.
Ah ok, I've always just gone into mass properties for each part and manually entered the densities but your way is much easier, I knew there must be a way!
As for the folds at the back I will have to see what radius I can bend them, not sure exactly how this hydraulic bending machine works so my plan is to start with the hardox and bend it then adjust the CAD to match whatever radius I get before making the rest of the parts to suit. I will ask if they are able to do a sort of chamfer bend with 2 45 degree bends spaced 10-20 mm apart.
Oh and on the GR02s my main plan is to use the new Ranglebox motors but if they cost an arm and a leg I will have to find an alternative, my hope would be that other people woudo switch to the new motors making some 2nd hand GR02s available. But I was just curious how mario mounted his wheels as I imagine a similar thing could be done with the Ranglebox ones.
Max, to fit the RC wheels to a GR02 or any other live axle I make a custom adaptor, Hex 17 or 24.
To ensure the hex staying put on the shaft, I glue it with Loctite 638 and tighten the setscrew.
I'll have GR02's for sale soonish, send me a PM, we can sort out a price. I will ensure Ellis doesn't lose a sale by purchasing a couple of extra sets of his :) btw your bulkhead is too thin :)
Ok, I'll send you a pm.Quote:
Originally Posted by Gabe01
Latest CAD:
http://i1261.photobucket.com/albums/...nt%20image.jpg
All Hardox is now 4mm but I have extended those front pieces back to offer more support to the drum. The front thin bulkhead is perhaps a bit thin, I'll see if I can find the weight to thicken it up a bit.
The front bulkhead doesn't need to be that thick, just as long as it doesn't flex much. I think Dave uses 1.6mm or 2mm ti on 720 without issue. I used 5mm ali on Drumroll and there are two gouges on it from the drum teeth, where it bent outwards towards the weapon after an impact. Was essentially hammering it flat again after every fight.
Thank to Ellis' brilliant suggestion of making it less tall I have made an entirely new CAD model:
http://i1261.photobucket.com/albums/...15820D50DC.jpg
It may well look exactly the same but in fact it is now only 60mm high and by down grading the motors from 775s to 550s I no longer need to have the gearbox sitting inside the wheels so the bulkheads don't have to have a massive 40mm square hole in them for the gearbox. By converting to metric it has also allowed be to slim down the bulkheads to 15mm rather than 3/4" and the fron bulk head has gone up from 1/4" to 10mm. All of this has saved tonnes of weight so all the Hardox has gone back to 6mm and it still had the 4mm HDPE around the outside for added protection though I may thicken this to maybe 10mm. Depending on the wall thickness of the drum there can be just enough weight for a 4mm Hardox top and bottom, though they may need a few holes in them. For now I'll use 6mm polycarbonate and see how the weight is doing.
First job is to make the outer armour so I will send this off the waterjet cutters soon. One thing I am curious about is what do people think about the fron end? Are the little 'wedgelets' going to get bent up as soon as I hit a joint in the floor?
A CAD animation to show the drum spinning from the side of the robot:
https://youtu.be/_GNU-DGZtZY
I'm still concerned about those wedges getting bent too easily by the floor/other robots and am not sure if perhaps they will get in the way of attacking other robots, but also think I will need them to get under other wedges to bring them up into the path of the drum. What do you guys think?
Whilst I'm waiting for parts to show up for the feather weight I've been working on the heavyweight.
Finally a full pressure pneumatics test:
http://youtu.be/nQHECcujhFk
Anyone got any advice on how to stop the bushing coming out the end?
Next step is to do the wiring with a decent removable link so I can have it driving around (last time the main power wires melted!)
Then just need to sort out a flipper arm and finish off the chassis, might see if I can switch to a front hinge as I think that would put less stress on the piston rod.
New idea for the design of the drum for the fw:
http://i1261.photobucket.com/albums/...91AB04488A.jpg
Exploded view:
http://i1261.photobucket.com/albums/...C13CE10977.jpg
What do people think? Is it likely to work or am I asking for trouble?
You'll need to re-evaluate those discs, they don't look balanced. Personally I'd try a similar design but with fewer, thicker discs or have the discs more of a ring type design and key them onto the drum - more money/effort but would be a lot less likely to fail
Oh yeah, forgot to mention that the disks would be re-designed so they were actually balanced! I just haven't got round to designing them yet
You will need an even number of disks to make it balanced with half the teeth on one side and half on the other; I would go with Matt's suggestion of thicker teeth and smaller spacers. Having a sandwich of teeth and spacers reduces strength and stiffness; the axle is the main part keeping everything straight so it needs to be really strong.
How is it held together along the length of the drum?
The whole drum would be slightly in compression holding it together. The bearings are set into the end of each drum so there would be a small axial load on the bearings.
The other thing is didn't mention was that the teeth would be made of some form of steel and the spacers aluminium, so weight becomes an issue as the teeth get wider! As it stands it shoud I be about 3kg
What is applying the tension? If you are compressing the drum via the bearings, you will need tapered roller bearings; ball bearings will wear quickly. The problem with this is that tensioning bearings too much really increases their rolling resistance, so you will be wasting power overcoming bearing friction, which will be dumped as heat in the bearings. Sorry to be blunt, but my gut feeling is that this design will bend and fail after an impact with another vertical spinner.
I'm guessing this design is to allow teeth to be replaced as they wear, which is a good idea. If that is what you are after, I would go for the same design as 720's aluminium drum. It is probably no harder to make and removes all the structural problems, plus that design is field-tested and proven reliable. Mouldy made the aluminium body of the drum really thick, but you can always reduce the weight with a larger bore.
I guess the 4 rods running through it could be threaded at the end with counterbored nuts at the end to compress the whole thing together, maybe I could redesign the spacers and the disks so they sort of slide over each other/interlock to improve stiffness of the system.
The idea behind the system is to be more easy to repair/replace sections and to overcome the problems Mouldy had early on with the teeth ripping out (he had to dovetail the teeth in or something I beleive)
Mouldy used a T slot to hold the teeth in, as least on the drum that I saw. The nice thing about that is the teeth slide right out once the end of the drum is removed.
Using the rods to hold the drum together will definitely improve the stiffness but its going to need CNC accuracy to get everything aligned.
T-slot cutter does sound like the way to go, I'm trying to see if I can find someone with a milling machine I can borrow.
Has anyone had any success with using cheap AVR programmers to hack the TZ85As? (Such as this: http://www.ebay.co.uk/ulk/itm/252087015960 ) The polulu one is pretty expensive and kinda defeats the point of hacking them yourself.
How about the programmer from Hobbyking? http://www.hobbyking.com/hobbyking/s...rSearch=usbasp
Its dirt cheap but only available from the international HK warehouse.
A tangent but still on subject, the above issue of assembling a drum weapon is one of the reasons I opted for a whisk on C3. Much easier to make and maintain (provided you design it right first time round!)
If you are set on a drum, look at 360's thread to see how Mouldy did the drum assembly on 720 and 722. Its one of the best example out there.
Alternatively you could do what Jamie did for Drumroll, but that had the flaw of welding the teeth on weakened the Hardox.
+1 for the whisk!
You could also look at the drum design on the Touro line of bots. They are bolted on (which I don't like) but I don't recall ever seeing their teeth break off.
Don't think the welding affected the teeth on mine too much to be honest. Was just a combination of tooth shape and a 26,000rpm impact between two hard metals.
Thanks Nick, the HobbyKing one will do perfectly.
Looking at the various versions of Touro they have used a variety of methods, welded teeth, bolted, what looks like a single piece machined snail drum, and an interesting design with essentially a flat eggbeater with two halves of an aluminium billet bolted on either side effectively making a drum.
Can recomend the T slots.... many huge hits and not a sign of failure yet.
Touro went from bolted teeth, to T slots, to dove-tail to snail drum... dove tail is best IMO but makes making the teeth harder
Right, I've got my TZ85As and hobbyking USBasp programmer, I've installed Atmel studio 7 and downloaded and installed a driver for the USBasp (from here: http://www.fischl.de/usbasp/). I've done all my soldering and all looks good. I'm trying to add a target in Atmel studio but nothing is listed under ports, I've been into device manager and can see the USBasp and it says it is working correctly, but even in device manager it is not listed under ports but under 'Atmel USB Devices'. Can anyone work out what I'm doing wrong?
The easiest solution i found was just using the kk multicopter flash tool, it is more than capable in flashing the tx85a with the hex-file.
Ah fantastic, that looks much easier.
For the board do I just put "atmega-8-based brushless esc (flash)"?
Edit: and did you have to power up the esc from a battery?