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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
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.
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?
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.
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.
http://i.imgur.com/Jjm739i.jpg
Edit: shown here with its full support jacket: http://i.imgur.com/WEmxpCa.jpg
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.
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!
http://i.imgur.com/OV0iEWP.jpg
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.
Hi, do you have any of these gearboxes for sale still?
The Saturns? Commercialy available.
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.
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. :)
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.
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.
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
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!
Why do you think I called the Saturn the Saturn, and not Jupiter. Room for expansion!? :)
I look forward to seeing what you come up with :L tbf, being a planetary box I guess you could probably use Mod 1 or similar just fine as it's spread across several gears; the electric winch I had was mod 1.5 with an alu ring gear, and that was rated for massive loads...
step 1 - Create new gearbox and call it the jupiter to annoy Ellis
step 2 - ??????
step 3 - profit!
Step 1 - create new gearbox and call it the Uranus.
Step 2 -???????
Step 3 - chortle immaturely.
Just for reference on MOD1 gears, the Lambert gearboxes on Gabriel that have the big Ampflow motors driving them, with the big and I mean BIG wheels 900mm diameter have first stage MOD1 and second stage MOD 1.5 these are a standard gearbox which is not nearly as good as an epicyclic (sun and planet) style gearbox.
so MOD 0.6 for the first stage and MOD1 for a second stage should be OK if you don't go silly on the power!
Remember when dealing with drives for combat robots, the limiting factor it the GRIP of the tyres. you can have mega power slides that look cool but that alone doesn't win fights. if you keep the power of the unit equivalent to about 1.2Kw brushed that will be enough for most applications. if you want another Brutus just have 4 of them!
I know people who have stripped MOD 1.5 on a Bosch 750 before... I just assumed MOD 2 was the standard for heavies. Impressed that the MOD 1 gears are working that well!Quote:
Originally Posted by craig_colliass
With brushless, it's worth bearing in mind that it's better to over spec the motor and run it below it's max power, as they have a lot less thermal mass to spread the heat due to being tiny and powerful. Most of these motors are designed to have a constant stream of air, EDF motors especially. Without it it is likely to get red hot if run at it's specified power rating. I'm looking at a minimum of 3kw motors for drive, and then limit them to ~1.5kw on the VESC, but if suitable cooling can be sorted then you may be able to use less. It's yet another one of those things that needs experimentation and combat testing to work out what size is right. (alternatively I could sit down and do some maths to work it out... but who does that? :L)
The torque a gear can handle greatly depends on the surface area of the contact patch, so a wider 1.5 Mod gear could handle the same torque as a narrower Mod 2 gear.
Also depends on the hardness of the gear material, the pinion gear usually is case hardened.
My first robot used Sinclair C5 motors that used a 5:1 Planetary gearbox with plastic gears. Was only 250W at 24V but I ran them at 36V and had no issues with the box.
I wouldn't use belts (personal preference), its the heavy, expensive, and doesn't allow for misalignment caused by being smashed by spinners! If space allows use chains, if tight on space, use gears.