Multiple outrunners to a single ouput

Late night heavyweight ideas are happening, was thinking of trying to get a high-power output through multiple brushless outrunners, probably something like having 3 or so NTM 5060s/SK3s timing belted to a single output shaft for use on a spinner or something along those lines. Normally I'd be a huge advocate of using a single big motor, however the only motors I've seen that would be big enough for what I'd assume I'd need are rather expensive...

I can probably aim for that (or just an Etek) if that's what it'd be better as but I thought I'd ask whether multiple brushless on a single output is a good idea or not. I'm relatively sure it's been done but to what success, I haven't a clue.

Thanks!

Simply put. No.

The esc's for non sensored brushless meassure the back emf from the motor to get an rough idea where the magnets are. On that idea the pulses (block waves) to the coils are calculated.

If you mix up 2 or more motors, the back emf will become an avarage, and the output of the esc won't be anything the motors can use.

I guess to overcome that issue, you could always put a freewheel on the output of each motor?

However, I wouldn't bother. You will struggle as it is to get a reliable spinner. Lets face it, everyone in the UK is rusty when it comes to what makes for a reliable heavyweight spinner these days.

You can do it if you use separate ESCs for each motor wired to the same signal input... It's done in RC aircraft and cars sometimes (HK even have a premade gearbox unit for it: http://www.hobbyking.co.uk/hobbyking...ox_EPS100.html)

Can't comment on the effectiveness of it, whether it does give double the power output or whether a lot is lost through inefficiencies, but it would likely be trickier to set up and get working reliably..

I believe in theory if you mechanically connect the motors and assemble them such that they are identically oriented and all three motors are identical and the ESCs will all behave identically, it would work great. In reality that isn't going to happen. That said it should still work, though I would just expect a lot of inefficiency, thus heat, thus reliability issues.

This, but with 1/5 scale inrunners, is exactly what Jerome Miles did for his heavy bar spinner last Robogames. It had buckets of power but couldn't get past 0rpm without help. A regular go kart centrifugal clutch (30 quid) should solve that. Also this sort of thing wouldn't exactly be cheap anyway, talking 3 motors and ESCs + spares, it's not too different in cost to more traditional approaches. You're also a bit limited in voltage with cheap hobby brushless stuff until you go bigger than NTMs, which also pumps the price.

Not exactly an answer but... Given old HW robots used Bosch 750s - so 750W of power - provided what you choose has more than that then surely you have a good drive mechanism. Its not like the old HW's were slow or anything. Tornado ran 750's on 36V and was like a missile. So anything modern with more than level of power should do fine.

If you could find an ESC that would cope then running a pair of HK4035's or HK5020's would be more than enough power. Yes they are expensive but if you want all out power then you get what you pay for, and if you treat them right then you should have no problems with them.

Going back the multiple brushless set up, Dave told me that the dual set up in 360 was a little pointless as no two motors were identical so eventually the weapon would only be driven by one motor as one would be more powerful than the other. So you would end up with the same issue but worse!

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Originally Posted by Eventorizon

Going back the multiple brushless set up, Dave told me that the dual set up in 360 was a little pointless as no two motors were identical so eventually the weapon would only be driven by one motor as one would be more powerful than the other. So you would end up with the same issue but worse!

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Hmm, didn't some people we all know build a dragster with six chainsaw motors and have it work quite well? I suspect that in a multi-motor drive some motors will be running hotter but that the power output will be the average of all the motors combined.

A centrifugal clutch might work, but it will need to be much larger than a go-kart size to handle all the power and the recoil when the weapon hits something. Didn't Sam have issues with the clutch in his new bot? I know he ended up removing it to improve the spin-up time.

If you wanted to equal the power of an Etek (Peak 15Hp, 11,190 watts), it will take 4.2 NTM50-60 motors (2,665W) so let's say 5 motors. The cost for the motors is about half of an Etek so its not a bad choice on paper. The ESCs are more expensive but still much cheaper than the recommended Etek ESC. Like Ellis and others have already said, there will probably be efficiency problems meaning that you need extra motors and batteries.

Hmm, I may shelve the idea then in favour of something a little more conventional, thanks for the help!

I know brushless motors aren't the biggest fans of being linked together, which is why I mentioned about the (smooth)belts to a drive shaft, allowing each motor to spin at its own rate I guess in theory. In practise though it's probably just going to be a whole lot of work to not as much gain from the sounds of it. Probably work out cheaper by the time I've done with the inevitable failures and replacements haha

There is a heavy just built in America that uses a series of brushless motors to spin up a full body spinner.

Yeah that was the main inspiration for this I guess, no idea how it performed overall but I know it didn't actually compete so I don't know if that's something to do with it... I am fairly sure that Touro Maximus runs a pair of Scorpion outrunners on the drum, after a bit of research, but I've no idea which ones, nor voltage or gearing, weight of the drum etc. It'd be an awful lot of guesswork on my end and potentially a lot of wasted money if I got it wrong.

I've seen the specs of touro maximus somewhere will post them when I find them.

http://www.scorpionsystem.com/news/robot_PUC/

http://www.riobotz.com.br/portal/ind...touro-maximus/

There you go, dual HK 5035's. I would bet they run both at the full 12S, nothing else makes sense. The drum weighs 27Kg and looks to be about 120-150mm in diameter.