New FW- doorstop

[Bodge Job]

Re: New FW- doorstop

What wheel size are you using? 100mm wheels with 24:1 and 18 volts is really pushing every thing to its limits, should work, it's just for how long is the question. I'm doing every thing I can to keep every thing cool in my robot and I still don't think mines going to last very long.

[Eventorizon]

Re: New FW- doorstop

If you can, buy some 24V fans from Technobots and fit one for each motor, the bigger the better. That might help them last longer. You could also bend some Heatsinks out of sheet copper and attached them to the motors with thermal paste.

We have a single 40mmx40mm fan on Binkys 160HV for the weapon. It has never got hot even in heavy testing! A bit of air circulation can do wonders :-)

[Ellis]

Re: New FW- doorstop

I don't see how motors working at their designed voltage on 100mm wheels is pushing it, really... It's only like having 16:1 banebots gearboxes and smaller wheels, same end ratio I mean. Plus we have four, so the load is spread out. If you're referring to Robob, I believe he's using 75mm wheels.

Also the issue with Robob's setup isn't the motors overheating at all, which is our experience with overvolting 12v motors to 5s, it's the torque they produce as a result of overvolting that kills the gearboxes. I'd still be running 12v motors at 18.5 if there were suitable gearboxes that can take the stress. The motors do get warm, but nothing more than I'd expect, and the power you get out of them is awesome.

[Danjr1]

Re: New FW- doorstop

best give a bit of background!

im using 75mm wheels and the gearboxes are very old. the output shafts are the same ones ive been using in my drill powered bots since my first event at the O2 so they were due to fail at some point. I can imagine the overvolted motors and increased speed will have exacerbated the problem a bit! luckily the GR02s will fit in nicely so ive emailed Ewan to get hold of the necessary parts (i just need the housings really). All just in time for the championships!

Only issues ive got now is the suspected ESC thermal protection breakdowns which i think are solved by removing all the tape from the motors and unwrapping the ESCs from the foam that they were wrapped in and a strange problem with my DX6i which i think is due to the mixing. For example, when your go full forward and full left hoping to stop the left hand motors and let the right hand motors bring the bot around, the reverse happens and the right hand stops, left hand carries on and ends up going right?! As i say, i think its due to the mixing im using which is the built-in elevon/aileron mix with the following set-up in the youtube video below to get full throws: http://www.youtube.com/watch?v=6Ewa79_9Iq4 . Any help with that would be great!

[ewan]

Re: New FW- doorstop

You shouldn't really have any problems running 18V GR02's at 22.2V, it's only a 24% increase, though of course you should take care to ensure the motors are well ventilated and aren't allowed to stall (which usually only happens in combat robots if a wheel locks or gearbox fails).

One thing people often forget is that if you start with with a motor designed for a higher voltage then the current draw will be lower which will help reduce the amount of heat produced - for example running an 18V motor at 27V (1.5 x voltage) should be less prone to thermal failure than a 12V motor run at 18V.

Another thing to add is that I've not yet had any gear or pin failures reported for the GR02's (famous last words..). A large number of these types of failure with drills seem to be related to how well (or poorly) the output shaft of the gearbox is supported, so do make sure external bearing are used for overhanging loads.

Will send a reply in a few minutes Dan!

[Danjr1]

Re: New FW- doorstop

im thinking that the pin failures might also be down to the grub screw method of locking the gearbox. When this is used, the ring gear will spin ever so slightly until the notches hit the screws. These slight but sudden stresses cant really do much good to anything that isnt effectively secured i.e. the pins.

In theory, could you silver solder the pins in?

Also, any tips for removing robo challenge wheels from the output thread when its been on there for years with a sh!t load of loctite?

[Ellis]

Re: New FW- doorstop

In ours we always lock them so that the ring gear can't spin freely, for both the reason above and that that slight play means that your robot has a delay on every input that involves changing motor direction, so you lose some drive finesse.

edit: we have considered solder but thought that (naturally) putting a blob of weld on the other side, between the bearing and the pin holder plate (there's a mm or two of space there) would be better still. That was going to be our fix for the champs but it's inherently unreliable, as it'll just move the point of failure to probably the gears themselves, so we opted to lose some power for the sake of reliability and go to 18v motors.

edit2: a decent set of these slim enough to get between the wheel and the bulkhead to grip the shaft works for us. Sometimes you need to clamp the wheel too, though a pair of gloves and some welly usually does it.

[Bodge Job]

Re: New FW- doorstop

that could work, with mine, as there a very tight fit, im super gluing it as it dosent warp or have any extra stress on the gear box

[Danjr1]

Re: New FW- doorstop

well ive now got two of the problems sorted. The GR02s will be ordered shortly and it was the thermal protection kicking in that caused it to breakdown. i ran the bot at full throttle in various directions for 3mins with no visible slowdown as before.

only issue now is the mixing but ill post that in the main forum.