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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!
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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.
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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.
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Change the reduction yeah. Maybes shove a planetary stage before the spur gears or something?
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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?
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Just using an identical 2nd stage sounds ideal - you already know it holds up in use. You might get away with a single stage Banebots P60 as a first stage but motors you want have too much torque for a 2 stage P60.
The brushless set-up I have is instant reverse and plenty of other ESCs have the feature, particularly the sensored ones. Its important to download and read the ESC manual before buying anything; the reversing details are often vague. There is at least one Hobbyking sensorless ESC that has instant reverse, I will try to find a link.
Another option is to add sensors to an outrunner. Its been done before and someone even had a kit for it. It only works for motors with a certain number of poles but that still leaves a wide choice. A sensored outrunner would be a fantastic resource for bot builders; it would offer low speed torque, instant reverse and lower cost.
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I found the sensor ad-on kit here: http://e0designs.com/products/hall-effect-sensor-board/
It only works with 14 pole motors and down to 50mm can size but that still leaves plenty of motors to choose from, including the NTM 50mm series. I might just have to try this out myself! If this works out, I predict an invasion of fast & reliable wedge bots
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Yeah, that's the problem with the Banebots stuff... at the most, it was designed for 775 motors I think, putting a massive brushless in it can only only end badly!
I shall have a look at the sensored ESCs too, I've found one non-hobbyking ESC that's got instant reverse but it's a little too expensive. Going to trawl through the manuals when I've got chance!
That's fantastic too, thanks! Though I have to say, if I can get that to work with a 2.5kw brushless NTM on 8s... I think that might be the scariest rambot known to man. That's like, 6 horsepower in theory? Crack a massive magnet in there and we're good to go! Perhaps the two-stage would be ideal there as well, though not quite as heavy a reduction...
Would definitely be a good thing for robot combat as a whole too, might make brushless a lot more accessible if it proves similar to high power brushed motors that seem to slowly be dwindling in numbers...
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Its hard to find an ESC that runs on 8S and has reverse. This HK one ticks the most boxes for me: http://tinyurl.com/ofe6mc5 its only capable of 6S but that still gets plenty of power out of an NTM 50mm outrunner. I think you need to get some MUCH wider & grippy wheels to make use of all that power :)
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Yeah, that's one of the ones I spotted, it seems alright! Perhaps not 8s but that's way OTT anyway (that said, that is the name of the game with HardWired haha!) might get some on order when they're back in stock...
Definitely too! I'm aiming for thicker wheels, but will definitely have better tread on there! I think I wore the current set of wheels out during testing, going to get plenty of spares made up next time! I'll probably use some kind of magnet downforce too if I can't get enough grip from the wheels, I think with that much power it'd almost be a requirement. I'll see how it performs though first and make changes accordingly! I'm definitely having a gyro in next year too, it'll help dramatically with the steering. It seemed to drift off to one side and spin during long run-ups which is a pain to deal with, but nothing that can't be sorted!
