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It may be better with a end support, can you get a bearing which the bolt head will fit into and drill a piece of aluminium and mount to the base, i think the problem you have is the sprocket drive is trying to pull the smaller sprocket, support it so it can't get stress on sideways movement should solve it
It has had a support on the other side of the sprocket since we started. That picture from a few posts ago is old, and doesn't show it. We have been super careful with the bearing, knowing the stresses involved could quite easily destroy it.
I'm off to once again dismantle the side of the robot (at least it's fast and simple, might take 5 minutes if I take it easy), as apparently dad has just bought goodies from one of the B&Q-type places down here that may help this.
We're not back to square one, quite, half way back perhaps but not all the way. I'm going to think about ways to avoid cottering (that should be a word, along with cottered!) all the way through the material and instead a little way from each side. Twice the failure point has been (as you'd expect) where we have drilled all the way through.
As well as that, we're going to turn the torque required to activate the limiter down.
I'll keep this updated throughout the day. Thanks for the comments and help.
Edit: and incidentally, the rest of the machine is working nicely. Famous last words, perhaps, but the drive rig as a whole, batteries-thru-speedos-thru-motors, is showing positive signs. The previous machine didn't get this amount of drive testing.
Any luck with the repairs?
As a last resort I'd suggest you ditch the reverse thread screw you're using, its too small at 1/4 diameter. A bigger diameter bolt will be much stronger. All you have to do is drill the sprocket, and drill shaft to a bigger diameter, say 5/16 (or 8mm) Buy an M8 or 5/16 24UNF taps and cut a thread in the drill shaft. Then lock all together using an M8 or 5/16 high tensile bolt. Then use a 3mm roll pin to cotter all together.
Can you post a pic of the problem area and the parts in question?
The reverse thread bolt we have is no longer in use due to a slight technical issue, by which I mean it's in two pieces. :P
And, we can't use a bigger bolt because the bore of the sprocket can't be any bigger!
We're really stuck. We're rebuilding it as we had it last night, and we'll set the torque limiter low. We don't have time for anything else. At least, we hope, it will work visually, it just won't be able to lift much before the limiter kicks in.
I'll post pics of the final setup tonight, assuming it doesn't break for a 4th time. We have decided to try and fill any gaps that will allow slippage (and thus enough momentum to break again) with solder. The alternative would be glue, so this works.
the amount of torque going through that sprocket, glue and solder wont do anything. I would really try and get it welded, its the easiest way without having access to a full machine shop.
We know, yeah. :|
Well, we'll build it so that it works nicely below major stress, and leave it. Discussing the potential of Mario welding it for us at MMM.
May just move the weak point to the next thing (gearbox?) which will probably be more expensive!
Agree...solder not going to help much, adhesives - depends, I've used adhesives which stick to metal like welding, but I doubt you have any access to those...I'd go with welding as said above. if you don't have access to welding I cant see any way out if not by up sizing the sprocket hole ( looking at the photo below you have more than enough space for that)
http://i1088.photobucket.com/albums/...2062012427.jpg
We could potentially up-size the hole by a mm or two (has been drilled out since that picture) but we're reluctant having experienced the power involved.
Well, Mario has extremely kindly offered to help. We think making it to the House of Chaos shouldn't be too difficult, in which case we'll have at least one skilled person leaning over the thing who will guide us. If he thinks a bigger hole is necessary, may a bigger hole be drilled!
I have a feeling he intends to just weld the buggery out of it, though. :P
We'll build this, avoid breaking it, be happy, and let Mario do the thinking if we can stop by. :lol:
good to know you found someone to help you out, it would have been a pity if it didn't work 100% after all the effort put in this build!
Have fun :wink:
In the end, it became welded. And rewelded after the first test. And made a spare that broke by looking at it. Wrong kind of steel for the axle.
That motor and gearing put a mountain of torque on that poor little sprocket.
Oh well, I hope the last fix I created will do the trick. We'll see at Maidstone.
If this doesn't work, I'll weld the bugger out of it.
Mario has been great with this, in both the results and the turn around time of new potential solutions.
The latest I believe was a single piece of steel, turned down to a shaft on one end (for the sprocket) then left large to screw onto the drill shaft, with dual grub screws.
If this breaks, I'll genuinely be surprised. Indeed, we shall see at Maidstone!
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My internet time is almost up so I'll keep it short in saying thank you to everybody at MMM so much for a fantastic event! We had a brilliant time, despite the issues obvious to those there (Mmm smell those motors burn! Hear those gearboxes strip!) we managed to come second in the main event, which was completely unexpected. All thanks to those who helped us out, many names escape me, but you know who you are.
For a first outing with our second robot and our third event ever, we're pretty happy. Pretty major changes will have to happen to make T2 more reliable, a rethink of our drive motors mainly, as well as improvements on the lifter control as the current setup is (electronically, I mean) clunky.
I'll try and do a proper write-up once we're through Maidstone and have a full damage report!
Ellis
Videos!!!!!!
Using a dongle which is excruciatingly slow, can't upload footage until we get back home really. Hoping others will start uploading as we're equally desperate to re-watch our/the fights!
We're home now, and the video uploading process has started. The first is this 10+ minute long hockey game. Was seriously fun, and our team won!
http://www.youtube.com/watch?v=vO8uDqntFsY
Some of the time is like they are standing still whilst you storm in and smash the puck out from under them, literally in the case of Satanix! We have to bring that to the UK!
Yeah, once I got the hang of it, my strategy went from score if possible but mainly don't break the robot to well it isn't broken so might as well headbutt everything, and it worked out well in the end!
I really must stress how much fun this was for the drivers and for spectators. Something like this would be brilliant at one of the HW events, instead of just sticking all the feathers in at once. I can very easily see it becoming a thing.
Satanix is the perfect shape for hockey!
Last time I played before this, my team won 6-2 and I scored 5, and helped with one of the opponents goals (Kashei rammed the puck into my front wedge and went right over into the goal :P).
Massive amount of fun, really should try it here.
If it's half as violent as air hockey games between you and the Big Nipper guys David, we're all in trouble!
i cant remember but if you said something about about burning out drill motor or knackering the gearbox but if it is to do with the motors i was thinking if you went for some 14.4v drill that had a 650 rpm output and over volted them to 18v you would only loose about 12 rpm and would put less strain on the motor
http://www.ebay.co.uk/itm/BRAND-NEW-GEN ... 4ced488dea
this is the same guy i get my 12v ones from and they seem better built than the last argos ones i got
Yeah, we're running the motors hard but the reason for them burning out is because of the gearboxes failing. Even if it were just the motors, I reckon those 14.4v ones are actually 12v motors overvolted. Doing the math, 550rpm (12v) overvolted to 14.4v gives 660rpm, give or take some. I'd say there's a fair chance those motors are actually 12v.Quote:
Originally Posted by plargen
Also the build quality might well be better, as it's slightly more money for just the drill unit. You're not paying for the battery(s) nor charger. Interesting!
probably might be worth you looking at the gr2 lol, might be more cost effective in the long run
just wandering what the sprocket pitch is that your using for the weapon and if the chain has broken also if you know what sort of load its broken under or if its just because someone hit it (that's if its broken at all)
It did break, but not due to the weakness of the actual chain, but the chain link that we bought. Broke twice. It's made of thinner, harder stuff, and under big loads it fails. This was fixed for us by Marien (thank you!) at MMM, but his fix (using the same/most of the bits that broke) failed again later on. I'd suggest you avoid a chain link and get a chain breaker tool.
As for loads, I don't know, it broke from a landing the first time and under stress from flipping something the second time. It's 6mm size chain from technobots. They have it rated at 300kg tensile strength.
As it says 300kg in tension. As its a steel, in compression it will probably be much less.
just wandering if you know the max NM torque of the drill because if you times that by the chain gear reduction and then covert it to kg-cm and then divide it by the how many cm long the lifting arm is then you will know the max weight at the tip
then you just need a means of stopping it from lifting the back end up
only worked out how to calculate the weight because i'm looking at doing drill powered lifter design
I don't really know anything about the drill as it was found next to the bins down the road! It can flip a FW comfortably, I'm just a bit pansy-ish with it because I'm scared of breaking something. Once the issues have been ironed out we'll do a maximum lift weight test and the torque should be backward-calculate-able from that.
Remember that you have to consider landing heavily etc, the weapon going full power one way and landing awkwardly on the arms in the opposite direction would result in massive stress.
Look forward to see what you come up with!
well so far i have a few different lifter arm designs the longest should be able to lift 40kg at the tip and and the shorter design about 70kg and that's using a 5-1 reduction from a drill it doesn't take into account the friction in the gears etc
might try doing interchangeable weapons
It has been forever!
We had intended to start getting back into gear before Christmas. Unfortunately Dad has been occupied with work, so things haven't moved. Until today, a little bit.
I took T2 out to the workshop after having had it sitting under the coffee table for several months, and started looking at the immediate issues left after MMM and Maidstone.
The main forks could move independently by about 5cm at the tips, and the sprocket seemed to have a similar amount of play in it. The result was huge looseness in the setup; the shaft could do, I'd say, an 8th of the full motion, without the forks even moving.
Happily it wasn't that the shaft (just a mild steel 20mm threaded rod) had been worn away by the M6 cotterpins we used, or God forbid twisted, it was just general looseness, so I tightened everything up. Also the little M6 bolts we used like setscrews to hold the sprocket to the shaft had worn away where they tighten to it, so the sprocket's play was from there. I replaced them with some stainless bolts that will hopefully last longer. It's all still a bit rickety but I'm happy.
Not really a lot to report, but it's significant because we (hopefully) won't have to do any major rebuild work to T2 before we move on to robot nºmero 3. Especially since April is suddenly just around the corner and we have yet to go beyond CAD with our concepts. I feared this shaft looseness was something much more sinister.
Other issues with the robot are a bit of the left bulkhead cracked off (odd for HDPE?) at MMM, which we will attempt to weld back on. We still need to sort the gearbox reliability, not sure how yet. There is sometimes a slight lag when going full forward/backwards then suddenly slamming into a turn. It lasts a few seconds, like the link between the tx and rx is delayed, then clears again. We think it's the rx aerial, so it should be simple to fix. I think that is pretty much it. I doubt there will be many additions before April, though I'd love to make the weapon act like a servo.
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Christ did I just write all that?!^ All I did was tighten some stuff!
Thats looking good, its a nice bot. And I was looking into a system (which is completely different but uses a similar set up with the shaft) but feared it would have bad twisting, which would be a problem with our design would jam if it twisted. So if your having twisting issues im gonna have to have a re think about how Im gonna do it. yours looks cool, would be cool to see how it preforms in battle first hand.
Ah well, we haven't had any twist issues. No signs of it, either. We will be taking T2 to the UK for the champs, which will put it through its paces, but I am confident the weapon setup will last. My biggest fear is horizontals (with our luck we'll have NST from the get-go again) completely removing it...
Better drive now though, the get in before they can spin up tactic is a little more plausible, I guess.
Look forward to seeing what you build!
With the drive you have now you should beat just about everyone from a standing start, so getting in before spin up with most should be possible. [Not Conker though, did a quick test a few weeks back and it gets up to the full 4500 rpm in less than a second, and is at 6000 in under 3.]
Side question: When you ordered your 85A ESCs from Botbitz, how long did it take for them to arrive?
Argh crap! Upload videos do want do want! And yeah the thing launches into speed, the problem will be aiming it before going full throttle fast enough to make it count.
The ESCs took quite a while. I think it was just under 3 weeks. There were several bank holidays at the time, though, and postage to Spain is always a bit interesting. Botbitz say there postage generally takes from 8-12 days, so we were a special case.
Hi guys, we're going to make our own wheels, and before I buy the wrong things, can I buy any 3/8UNF size nut? It would seem there are loads of slight variations, am I safe with anything labelled 3/8UNF?
I am looking at these (or similar) in particular: http://www.ebay.co.uk/itm/3-8-UNF-25mm- ... 5891b47a4b
Thanks.
lol they look familiar
i was using these
http://www.ebay.co.uk/itm/3-8-UNF-Femal ... 3cc8b87228
but im now using these
http://www.ebay.co.uk/itm/5-X-3-8-UNF-B ... 415b3c8afa
and this lot work out cheaper
http://www.ebay.co.uk/itm/3-8-UNF-x-24- ... 27c7eb7d75
but i found you either need to drill the wheel bore to 13mm to hammer them in or heat it up first and force it in or it will split the wheel
heat up the nut, I used a 150w soldering iron for the job and left the nut on the end for 5min or so, then press it into the middle of a wheel that has been drilled out. 13mm should do the job fine.
The thing you have to watch is that you get the nut in straight. If it's even slightly off then your wheel will wobble.
Once pressed in, I'd use the iron to cover over the nut to keep it captive within the wheel.
Yes, we're going to make up a jig with the drill press, which should hopefully keep things straight. Or straight enough, anyway. We have a heatgun, which should be easily powerful enough.
The bore of the hubs we have is 12mm already, if we can manage to get the nut in without having to drill out to 13mm (happens to be a size I know we don't have) then that should further maintain alignment.
My question was just to ask if any old 3/8 nut will do.
Thanks for the links, Peter.
as long as its a right hand thread and it says 3/8 unf then it should be