HardWired II

[mrsam]

Hatchet 2 will be very Thor/Joule esque in it's design so angles will be a given i think, i was thinking alu for the base but if i can get a suitably sized hardox offcut for a good price i may go that route providing i can get it in weight. Definitely no 90 degree angles on the next one!.

[Flag Captured]

Not a bad plan at all! Just need to be careful on the grade of aluminium you get, but I'm sure that'd be suitable - Hardox or something that strong would probably be better, depending on the forces at play with your axe and whatnot - I doubt it'd bend with it being a bulkhead construction but better safe!


In other news with HardWired II, it appears to be dead. Namely, one of the ESCs has just stopped working, which is very weird... they're TZ85As but one of the two just isn't powering up which is odd. Going to see if there's a connection break somewhere, there shouldn't be but testing it on its own should solve that. It doesn't smell like it's blown, so it's got to be some kind of break or the ESC has literally just packed in - I doubt it being the latter, given the proven resilience of them but I obviously can't rule that out if it comes to it. The next one will definitely have neater wiring, I know that for sure...

[mrsam]

Hmm that is strange, probably just a loose connection though, maybe that impact from 720 caused something to come loose. I doubt very much it's broken/burnt out as i think you would have seen something or smelt something, tbh though if it has gone you can get one from hobbyking unhacked for around £25 and i'm sure somebody will hack it for you if you ask nicely.

[Flag Captured]

Indeed, I thought it was 720, but I had it working after that, before I went home... It'll be fine though, it'll just mean I upgrade to brushless a little quicker! I'm sure it'll be nothing major, there's no reason for it to have blown, I'm fairly sure it'll be something and nothing but if not it'll be alright, I'm only using them for HardWired I I think now, 2 and 3 will both be brushless

[mrsam]

I would have had them off you but if you're saving them for hardwired that's okay, in sure you'll get it fixed like you said it's probably nothing major

[Flag Captured]

I might be, a friend wants HardWired I to drive next year (may be looking to upgrade it to an LP flipper instead of a lifter) so keeping it as basic as possible drive-wise is ideal, and brushless... I'm not sure how easy that'll be to drive yet. I know it needs time to speed up, like brushed are instant torque whereas brushless take their time to get up to speed, so it might prove a bit more awkward to drive. I'll be able to manage it regardless since I'll be able to practice with it, but they'll literally have to drive it on the day so yeah...

May sell them on someday though if plans change, will let you know if you haven't got any by then!

[mrsam]

The brushless drive may take its time byt that might work in your favour, if you think about it with most brushed systems if you gun the throttle you just get loads of wheel spin, the slow start up of the brushless might actually mean you get a better start.

[Flag Captured]

That's true, it could do but if I solve the grip issue, it'd be more of a hindrance than anything.

Also to note, whilst the tires shredded quite heavily during the champs, it turns out I'd not put the screws in properly after adjusting the tread pre-champs, so they were sticking up above the tire more than they should have done, basically I ran on the screws alone for most of the event... nobody to blame but myself for that one!

I was having a few thoughts on the brushless system, I could use a hybrid system - instead of using just sensorless, I could use that as a 'turbo mode' and have some brushed torpedo 800 motors for my low-end drive. It'd be a squeeze to get in, but it'd mean I have the best of both worlds in a fashion. Could always downside on the brushed motors, I don't need those to be my main drive, all I need is something with enough torque to still push things about but slow enough to give me plenty of control.

It'd kind of be like Firestorm's differential in theory, I guess. No idea if it'd work, but if I could fit the brushless motor/s to a forward/backward switch on a DX3, or maybe even program it in so that it kicks in when I've got the throttle for the main drive at about 50% or something.

The lack of start-up torque would be a killer for turning just on sensorless brushless, perhaps a dual brushed/brushless setup is the way forward? I'll see how it works in practice first before mucking about with a hybrid system though, I've never driven a brushless machine so I can't really comment on how effective it is!


Edit: Actually, that's a thought... how would a removable link for a Firestorm-style differential work? Not that one would fit in HardWired II, but it might work in something else potentially...

[overkill]

Depending on what motors you use, brushless drive should be as fast and responsive as a similar sized brushed motor. You probably want far more powerful motors than the 540 sized ones I use in Mr Mangle. Look around for 1/8 scale motors like this: http://www.hobbyking.com/hobbyking/s...or_1900KV.html



I haven't used that exact motor but its the size I would expect to get a heap of torque from in a featherweight.

[overkill]

Oops, didn't read your post until I had already submitted mine. Basically, sensorless drive motors are rubbish in robots and particularly at low speed and when reversing - go sensored motors for torque and precision control

[Flag Captured]

Cheers Nick, I'll give them a look!
The only problem I have is that I can't seem to find any that are affordable and a low enough KV rating to work on my current setup, which means I'll have to go two-stage or planetary, which is just more stuff to go wrong but if it works it'll be fine! Especially considering I'm a rambot, sluggish turning could be a bit of an issue... it's possible that this 4.5:1 reduction might solve the low-spin up of the sensorless, especially with a low KV motor, but there's not widespread usage of brushless for drive so there's not many accounts of them. Definitely that startup is potentially a killer though, especially with machines like Beauty 2/8 that can just flip you straight out of the ring. Guess that's what testing is for though!

I've been having a chat with Mario about using the NTM 42-38s (sensorless) on my current gearing, I'll probably give them a go at the Barnsley Robot Wars event this year and see how they get on - I've got another project that's using the same motors so it's no loss if it's not as controllable as I'd like... Definitely liking the sensorless though, still open to changing ideas though to get the most out of the drive.


How did you get on driving Mr Mangle at this year's champs by the way? Was meaning to ask you but completely forgot!

[overkill]

The KV of those sensored motors is a problem if you want to use your existing 4.5:1 reduction. According to a great engineering article I read, that's also not ideal for sensorless drive either. After showing some maths and test results, the author concluded that a higher KV motor with over 20:1 reduction worked better than a low KV motor. That was for powering an electric scooter with outrunners but I think the results will be the same at smaller scales. The other problem with a low reduction and sensorless motors is that low speed manoeuvring is very jerky as the motors go from stationary to a relatively high speed. A large reduction smooths that out a bit but your 4.5:1 won't.

Sorry to pour cold water on your plans, its just a combination of studying other people's issues and local experience - I'd rather you got a good result first time rather than putting up with problems. Can you add another 4.5 reduction stage in the bot? That will give you a very handy 20.25:1 reduction that will work with a wider range of motors.

[overkill]

Almost forgot: Mr Mangle drove quite well - you can probably tell that I am the world's worst bot driver . The only things I am changing is increasing the braking in the ESCs to 100% and increasing the expo steering rates in the transmitter a bit. That should take out the over-steer.

[harry hills]

Change the reduction yeah. Maybes shove a planetary stage before the spur gears or something?

[Flag Captured]

Oh no, you're not pouring cold water on anything! I'd rather have as many opinions and accounts as possible, helps me design something that's more likely to work well! I'll still be getting the NTMs so there'll be nothing lost, but if that's the case I might try and squeeze the two-stage in with some beefy sensorless motors. Depends which method would be the most size-efficient and lightest, but it's definitely a good idea! I'd quite like just a pair of gears similar to the ones I have now over a planetary, but I'll see how I could make a planetary that'll have enough strength to stand up to that kind of force...

Good to hear Mr Mangle worked well too, it seemed to handle pretty nicely I have to say! Did the motors have to come to a full stop, then brake before they'll reverse or was it more or less instant?