inrunners or outrunners

[widow_twanky]

Just trying to get my head round brushless for heavyweight drive.

Most of the gearboxes I have are up around 15 or 20:1, this means the kv rating for outrunners seems a bit low for an outrunners.

For the same money as a 3kw 63mm 200kv outrunners motor I can get a 7kw 58mm 650kv inrunners motor.

What are the pitfalls of this and why do most use outrunners?

Thanks

Andy

[maddox10]

Outrunners have a way better startup torque. But with a 20-1 gearbox and a decent 8" wheel, that 650KV inrunner on 10S LiPo gives you 18kph.
Combine that with the Vetter/Mangled ESC, and you have probably the successor for the classic Bosch750-4QD setup.

[Eventorizon]

Depending on if the build is for Robot Wars or just an upgrade for an old HW to run at the live events, you may want different speeds, which is a pain.

I looked at these motors early on for our HW (I think at least 1 robot ran these at RW this year) - http://www.hobbyking.co.uk/hobbyking...ner_Motor.html But the Kv is far to low for your gearboxes.

There were also these - http://www.hobbyking.co.uk/hobbyking...ize_heli_.html But the 5mm shaft is pretty dubious, or the Aquastars - http://www.hobbyking.co.uk/hobbyking...ess_Motor.html wich you can run without cooling.

You may need to rely on acceleration curves to reign in a higher KV motor if you cant find a suitable lower Kv one, but that's pretty easy on the new DX6.

What size wheels are you looking at/or stuck with?

[widow_twanky]

I was actually looking at something like this http://alienpowersystem.com/shop/bru...-720kv-12000w/ probably running at 8s. Gives around 20mph so would need dialling down on the speedo/tx but that's fairly simple and running stuff well within its capabilities is a good thing.

[Ellis]

Might be worth looking at large scale RC helicopter motors. These are kind of the best of both worlds, with good torque (they're outrunners) but fairly high KV. They tend to be compact but have substantial heat dissipation ability. Not cheap but if you wait for deals and scan Ebay from time to time you can normally score big brand gear at good prices.

This is one of my 800MX 520kv Aligns with the shaft replaced. The stock shaft is fairly useless (pictured to the right) but it's 10mm diameter inside the motor, and replacing is easy enough if you can get the shaft out of the endbell. Mine needed a proper press, the press fit is impressive. These handle 12s and several thousand watts.



Edit: shown here with its full support jacket: http://i.imgur.com/WEmxpCa.jpg

[craig_colliass]

For me what I'm looking for is the equivalent of a Bosch motor run on 24v coupled to a 2:1 reduction, gearbox.

This would have an output shaft of about 12mm a speed of about 1500 - 2000 rpm and a stall torque of about 22Nm.
this could then be fitted to a robot with a chain drive 4:1 giving a wheel speed of 400 -500rpm
I was wondering if the Ranglebox gearbox is man enough for that if coupled with a brushless motor and speed controller.

The idea is for a no frills drive unit that would be a lot smaller and lighter than current drives, but give similar performance.

[Ellis]

Craig, this is the setup I put in my feather for last week's Champs. It's a 2.4kw inrunner, through a standard 16:1 Saturn, running 5s LiPo. The motor peaks at over 30,000rpm on this voltage, so pretty abusive on the gearbox, but no ill effects as far as I can tell after a number of intense fights. I'll strip the gearboxes at some point for a closer look. Of course, two of these were pushing just 13.6kg, shoving 100+kg is a different animal, but it's promising!



And the units in the machine: https://dl.dropboxusercontent.com/u/...3/_MG_9144.JPG (thanks Mark_m)

Another option is to machine down the ring gears, and use only the second (beefier) 4:1 stage as the first stage of a compact HW scale drive system. I think that would be pretty robust.

[supernova]

Hi, do you have any of these gearboxes for sale still?

[maddox10]

The Saturns? Commercialy available.

[supernova]

Says out of stock on the site. Was looking at using it for a HW drive but MOD 0.6 gears may not handle the torque.

[Ellis]

I'm out of stock for a while indeed - will make a post on the Ranglebox thread when I have more. And yes, they're mod 0.6, which is plenty... for a featherweight.

[maddox10]

Mod 0.6 won't handle the strain directly.
But with an additional gearing that takes off the strain from the gears in the Saturn, it could be an option.

In Bullfrog, MOD1 gears are just enough to survive. But those are custom made and wider than normal.

For a new Heavy, we will go for a cascade. Mod 1.5 on the first stage, mod 2 or bigger for the last stage.
Just to cope with wear and tear over the years.

[craig_colliass]

Looks good Like I say in the first comment I would not put a wheel on the end of the gearbox shaft, but run a 4:1 reduction to a 200mm or smaller wheel. the speed I would be looking for is no more than about 10mph. if anything the power of that motor might be a bit high at 2.4kw.

[supernova]

Hi Mario, you make a good point, with the torque being transmitted through 3 planet gears.

I Would be interested in one of these gearboxes when back in stock.

Suren

[Rapidrory]

I'm looking at using heavy duty timing belts instead of spur gears for brushless drive, as the weight of the gears detracts from the weight saving of having lighter motors. If I can get my mill to make some UHMWPE pulleys for it then even better (I'm not sure if 3D printing would quite cut it at that scale). Ideally I'd need to find a suitably low KV high power brushless that can use relatively low ratios to help stop the belts stripping on the smaller pulley. I've found a perfect setup for feathers (1.5kw 190kv motor on 6s, 4:1 to the wheels) but haven't really looked into heavy setups for this just yet.

Just as a note, VESCs don't really like high pole count and/or high KV motors too much; anything above about 80K ERPM max and they become a bit unstable. (ERPM is the RPM x the number of motor poles / 2)

By the sounds of it Ellis you might need to look into designing a 'Jupiter' gearbox soon!