Team Bodge Job

That is definitely odd. Our motors sparked hard but never blew on their own, 100% of their failures were due to being stalled on the end of a locked up gearbox. I suppose if the gearbox were really resistant (debris/wrong grease?) and you were literally banging the motor back and forth at high RPM, it could blow, but even then I would expect it to just spark a lot and get hot. Not healthy for it but not fatal. You could experiment with another motor, yeah, you may have had a dodgy one all along.

yeah I thought it was a bit odd, the gear boxes moved easily, and the grease wasn't to thick. and it was back and forth a few times, but not a massive amount? i think the drive motors current should be limited a bit any way due to the speed controllers. but its the axe one im mostly worried about. being turnt hard back and forth. Should I change it for an 18 volt motor from gimpson?

If you want it to last, yes. I don't think the motor is at risk, though it will deteriorate faster than in other applications, the risk will be in the gearbox. Slamming a weight back and forth, plus having an olvervolted motor, I can't see it lasting long.

If it's a 36:1 gearbox you could make it 18v and change to 24:1. You should still have loads of torque to swing it round and you'd have a more reliable setup, whilst making it faster than it is at 12v in those tests.

edit: you may find it lasts longer if take some weight out of the weapon head, too. If it's a kg or two then the momentum behind it may just destroy the gearbox when you use it in anger.

Perhaps before you do anything you just build it as planned. If it breaks, you have options, if it doesn't, you have a powerful weapon.

yeah ill just leave it for now, I should have a proper test Sunday, and then a years improvements for the champs. although i cant make many other events this year which is annoying. I hope there's another RC Autumn thing, preferably with fighting so I can get some spinner testing in before the champs next year.

wired it up completely now, although the motor wires are to ridged, so im going to change them from 14 awg to 16. and one of the speedos is still glitchy so i have contacted dimension engineering. And depending of if the snow has cleared I may give it a test tomorrow on 18 volts, but the drive wont be working as only one speed controller is working properly.

I have also weighed it and it weighs 13.4kg with no top, so im going to have to loose some weight somewhere if I want a sustainable top.

undoubtedly the best conditions to work in... :P

Now that's dedication! I've bought what work I can inside though a day or two in the shed will be needed soon if this snow doesn't clear up

Yeah! im not sure why im so eager to get it finished, I dont have an event for another month!

Done a little work, new base and back. and did 18 volt testing, and the motors definitely don't like 18v :uhoh: . so going to change to a 14.8 volt lipo (i presume i have to buy one and that people dont want me taking a cell out of the current one?).

I changed the base plate for 6mm HDPE to 5mm HPDE to save some weight. And the bake was replaced so the robot can run on the back wheels at all angles. And to make it easier to have a strongish the top at the back. + it looks awesome!

and I can finally say:

little to no work on the bot, just tested the robot on a 24:1 gear ratio as the last one broke at 36:1, but that broke too! may change it to 2 speed 900 size motors (stolen from bruiser 2) and use them, but i don't know if they would have enough power to self right at the small 5:1 ratio, what do people think?

here is the video on Ben's build diary, http://www.fightingrobots.co.uk/thre...688#post440688
thanks ben!

Speed 900 clones at 5:1 would most likely not even move the axe properly (rule of thumb), let alone self right. They definitely have the power, but only after a lot more reduction would you see the sort of power you're getting from the current setup (the 120-180:1 ratios the 550s are running should say it all, you need a lot more than 5:1!)

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Next step, I'd say, is try and either get a normal drill in there or a larger drill. You can have the torque limiter still in place, which should help take up a lot of the stresses. If it is the pins on the gearbox shafts that are coming loose and letting the gears strip then there are quite straight forward solutions to that.

now thats a good idea, i didnt think about the torque limiter on drills, that could work! i think i have a small drill motor free so i could set that up and try that, thanks!

If you want to save a bit on space, just go with the traditional grub-screw fitting on the drill instead of having the whole torque limiter setup in place. You can still have the torque limiting just by screwing the grubs down a little less than what you would for drive. It'll take a bit of trial and error though to find the sweet spot between having enough torque to swing the axe but limited enough to slip once you've hit something.

yeah, thanks, i think it would be best to try it with the torque limiter first, as i think it would be eaiser to test, and get the torque right, but if i have to i will change it to that, i just think it would be good if i could make adjustments without taking the whole thing apart.

thanks though its a good method to fall back on

found the problem with the latest motor damage (ii had presumed it was the gears stripping causing it to spin, but instead it turns out the gear on the motor has come loose). And ive never had this before. The gears are only pushed on like the some of the older drill motors i first bought, rather than the later ones i got which had the flat.

Was wondering if there was a way I could reattach it on well? as if i try another motor i fear the same thing is probably going to happen with the stress of the motor? there appears to be glue one some of the motors gears probably to help with the push fit, but if that wasn't strong enough, how do you think i should attach it?
could attempt to glue again with the torque limiter and see if that prevents it, or could i somehow weld them together?
what do you think as im unsure, or should i just do a few tests?

If you have any old motors with the flat, use one of those? If not, we have had success with a drive motor by crimping the motor shaft (by which I mean hitting it with something very hard and sharp to misshape it), repressing the gear onto the now slightly distorted (be careful not to bend) shaft, and using a decent two-part metal glue. Can't remember how many fights our fix did, 10 or so, with no problems. :]

yeah problem is its a different gear so doesn't fit the shafts with the flat. i may try welding it first, and then grinding it flat as i think that will be pretty strong (and i dont have any desent two part glue atm) will practive on an old burnt out motor first though and if that fails ill buy some glue.

i guessing you have a tig set if your gonna try welding it

The motor shaft material might not mind you welding, but of course bear in mind on the other side of the front bearing there is a lot of glue and plastic. Might be worth opening on old motor, seeing what it looks like, close it back up to test weld it, and then seeing if it looks molten or damaged on the inside. If it does, eh...

As for welding the pinion on, if you try to weld the drill shafts they become weak and brittle (something to do with the way they're made) and the gears, as I believe they're made in the same way, may suffer from this too.

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If the motor test weld goes okay, can I suggest you put a small blob of weld on the shaft, then file it down to just a fraction too big for the bore of the gear and try repressing the gear? Essentially the same thing as crimping but you're adding material instead of misshaping it. The shafts are quite tough, you can support the back of the shaft on the other side of the motor and hammer quite hard fairly safely. Just trying to avoid welding the gear as I think it might make it useless.

if i remember correctly with welding the weld itself is strong but there is a patch around it that becomes weak due to the heat, its the bit to do with annealing i think (the rat that steel get cooled cooled affecting their properties)

not 100% but that sortof what i remember from my welding classes 7 years ago

well my welder is actually mig, and i did a lot of testing with the other burn out motor, the insides seemed to turn out fine, i think the brass busing seemed to help act as a heat sink, and the gear seemed to turn out fine and it hasn't weakened a noticeable amount (i tested it thougherly with a hammer) and the weld I did could be ground down enough to fit in the gear box and work.

when i did it on the actual motor and gear it worked fine, just got a small amount of the weld to close to the teeth, so i will have to file that down and sort it out when i have access to my good needle files and dremel. I have tested the motor (out of the gear box) at it all works fine. so im pleased with the results. just will have to test it properly when i have finished.

thanks for the advice though.

Fitted a drill motor with the torque limiter.

http://www.youtube.com/watch?feature...&v=jn4wnMjGVuw

http://youtu.be/jn4wnMjGVuw

What broke or didn't work:
The gear box was a little loose (internally) as it didn't have the correct number of spacers and the mount caused it to not be able to be tightened completely, so this meant the torque limiter wasn't working completely (it was on the tightest setting on the video)
This looseness meant one of the pins for the gears came out, which jammed the gear box and caused a partial gear chip on the middle gear holder due to uneven load, and the weld broke holding the gear onto the motor as I ground it down to much, will try a different attachment method.

So over all I think is fixable, and means i can change the torque limiter next time so it doesn't loose all its power in the swing, as it felt so much slower than last time, and decreased in speed quiet a bit at the beginning, but im not sure what caused that.
but it was not caused by the battery.

I have fixed it up and sorted it today, i added more spacers into the gearbox, this mean the torque limiter can be set at a higher level.

I have done some testing (with the axe module out of the robot so i can change the limiter easily) I found a good torque amount, but I found that all the screws loosened on the gearbox over time, which meant the torque limiter loosened. Im unsure how to stop this, would lock-tight work on this plastic? for the 4 motor ones I could probably drill them though and bolt them, but would make it hard work and awkward to undo. so probably not a good idea. But do you think lock tight would work?

You could mount it like in Tormenta 2 so you support the back of the motor and hold the motor together so those screws no longer do anything.

yes i could probably quiet easily put a plate around the motor to hold it together.
I also did quiet a but of testing and did some worst case scenario stuff as it was running well (like changing direction mid air) ad i did that for a while until the motor burnt out! but i think it will be fine in the end, not as powerful with the clutch, but oh well. and i will stick a permanent cooling fan onto the motor, so it cools down between uses, as the internal fan isn't much use on an axe, so it gets quiet hot, but with that I think it will be fine.