Drive motor options

[Liftoff]

What's the lowest ratio you can get from them Mario?

[maddox10]

Those are both custom sets. The Skyfall set is using ring gears from a wheelchair.
Firestarter uses homemade 7075 T6 ali ring gears. Kos (Builder of TAN) started those by building an add on tool for my small mill.

To fit in a 54mm diameter wheel.... with thin walled bronze bushings and a very thin rubber layer (is that needed for you?) I guess I can fit a 36mm diameter motor in such a setup. But the motor and gears will stick out on both sides of the wheel, as I don't know any brushed motor 36mm diameter that is shorter than 40mm.

[Liftoff]

I take it those are custom built boxes Mario, right? They look well suited for my use if they can fit inside a 54mm dia 40mm wide wheel.

Better stick to brushed motors then, rather than getting into problems controlling a brushless setup. That said I think I've seen a local team using a brushless setup on their robot...not sure tho as I only saw a photo of the underside and what looked like two brushless motors. Will try to find the photo and post it here, maybe someone can identify the components.

[maddox10]

Good, saves me the thinking! Any links to the gearboxes?

Firestarter
http://www.bugs.nl/media/album/view....J0ZXIvOS5qcGc=

Skyfall with explanation
http://i172.photobucket.com/albums/w...ps104ee1f4.jpg

[Max]

The other thing I thought of was using the newish brushless dewalt cordless drills- I imagine this could provide a good brushless motor with the appropriate gearing already made up so it can give the same speed output as a normal drill.
I dare say these new drills are expensive and parts will probably have to be machined to hold the motor and gearbox together but I guess it's an option if you can find a speed controller.

[Ellis]

Brushless motors go plenty low enough in rpm. Lower than equivalent diameter motors by far in some cases; the 775 can motor that Banebots use do 20,000rpm at nominal v.

The motors themselves are suitable, the issue is with speed control. It's hard to find a brushless speed controller that will not only do reverse, but not have a delay between fwd/rev. Some RC-car speedos do this, but they're generally lowish voltages (3-4s). Also, brushless motors can't just have their polarity switched to bang into reverse like brushed. They have to come to a complete stop before being able to change direction, further reducing drive responsiveness. Not many have experimented with brushless drive as a result, though once the speed controllers exist, the potential is huge. They are massively powerful.

This Australian build thread shows a machine with brushless drive, but there isn't much detail: http://robowars.org/forum/viewtopic....=asc&start=615

[Liftoff]

Skyfall uses that idea, as well Firestarter (Dutch Feather using Astroflight motors). And that's the current feathers.

Project One and Two used the same idea a decade ago.

Good, saves me the thinking! Any links to the gearboxes?

Another thing, was discussing the options for the motors with my brother (he's more knowledgeable on electrics than I am) and mentioned brushless motors, are they suitable for combat robots? The main issue I see is gearing them down to a reasonable speed, but otherwise they seem to be smaller lighter and more powerful to their brushed counterparts....
I know I'm asking too much, but while I'm at it I prefer to evaluate all options to make an informed decision and save myself from ordering needless or wrong parts!

[maddox10]

and got this idea of a compact planetary gearbox which could stay inside a wheel. ..have to think about this some more, put it into writing and make some sketches before I forget.
Will explain myself better when I get a clearer idea myself of what I'm talking about!

Skyfall uses that idea, as well Firestarter (Dutch Feather using Astroflight motors). And that's the current feathers.

Project One and Two used the same idea a decade ago.

[Eventorizon]

I think 720 uses the 16:1s with 775 motors, this will give you a rough idea of speed:

EDIT: Forgot to add, that's with 98mm wheels.

Wow! thats seriously fast!...hmm...to be honest I think I like the idea of something that goes that fast!

Yes, that is correct. Dave says that it wheels spins like crazy but it still gets good acceleration. Conker 3 is running the same set up but with 4x 73mm banebots wheels. That obviously wont have such a high top speed but it should accelerate like crazy and have almost no wheel spin.

[daveimi]

"...got this idea of a compact planetary gearbox which could stay inside a wheel..."

Tanto uses this setup

[Liftoff]

Just landed a couple of min ago, and having nothing to do on a 3hr flight I got myself through a lot of immaginative thinking regarding gearboxes etc...and got this idea of a compact planetary gearbox which could stay inside a wheel. ..have to think about this some more, put it into writing and make some sketches before I forget.
Will explain myself better when I get a clearer idea myself of what I'm talking about!

I think 720 uses the 16:1s with 775 motors, this will give you a rough idea of speed

Wow! thats seriously fast!...hmm...to be honest I think I like the idea of something that goes that fast!

Ellis, the wheels are 64mm in dia but with the track on, the effective dia becomes 74mm so that's close to your estimate. Regarding the added stresses on the tracks on skidding sideways, you're probably right...but they ain't going nowhere. The way they're mounted now its impossible to throw a track off...so might as well give it a try! Honestly I doubt it will side slip much with tracks, they're quite grippy!

The sabretooth, well if statistically it should be able to drive both motors I'll go ahead and use it, useless having it there to gather on dust! It's more honourable for it to die in battle!

[RogueTwoRobots]

I think 720 uses the 16:1s with 775 motors, this will give you a rough idea of speed:

http://www.youtube.com/watch?v=FIWcBXnDbI0

EDIT: Forgot to add, that's with 98mm wheels.

[Ellis]

I don't know if that ESC will do the job. I have heard the same general dislike towards them but have no experience, and can't really comment. Statistically they should handle two 775s fine. Statistically. Two TZ85a speedos from Botbitz would do it.

As for speed, I don't know how big the driving wheels on your tracks are, but at say 80mm, you'd get about 11mph/18kmh. That isn't crazy fast. Many machines are that fast (Tormenta 2 does about that) and faster. I imagine it'd be more a worry of if the added stresses from the speed increase would cause problems with the tracks. Skidding sideways to a halt from 11mph will make the tracks work harder than from say, 5mph.

The Magnum gearboxes and motors would garner around 8-9mph, again assuming 80mm driving wheels and 18v. They're more expensive but potentially the better option, they look a fair bit chunkier and the added power/reduction won't go amiss when shoving a tracked machine around.

Plus, more speed = more cool factor, right? Right!

[Liftoff]

So how's the speed like with the banebots 16:1? I mean are they driveable or it's like having a loose firework! And what about the esc? I got the 2x60 sabretooth, will it handle the 775 banes? I know there's a lot of bias against them, but as I already got it I just want to know if its outright incompatible or not

[Ellis]

Here's their site: http://banebots.com/index.html

In their range of gearboxes (the p60 sizes) suitable for 775 motors (a step up from 550s), only the 16:1 option is close enough to useful (next closest are 4:1 and 64:1). It makes for, at nominal voltage, an output speed of roughly 1250rpm. That is a lot faster than those 36:1 Gimson gearboxes, yes, which spin at around 550rpm. But I'd expect the motors to handle it, they're very punchy.

That is your only option for the 775 motor range from banebots.

They sell many more ratios for their gearboxes suited to 550 motors, including 16:1 again, 20:1 and 26:1. I didn't bother mentioning those above because they're basically the same motors as used in Gimsons, and the overheating problem would be the same. Worse, perhaps, due to the lower reductions. The next reduction up is 64:1, which would make for a very slow robot.

You can get 775 motors coupled to "Magnum" gearboxes, which are 20:1. http://www.robotpower.com/products/magnum775_info.html - looking at 650w from one of those at 18v, I should think that would be enough! Makes for about 900rpm, again at 18v. They look very very solid to me.


It may be cheaper to come up with a custom solution?
----

As for smaller shafts, I have never seen that on Banebots, but take a look at their (dodgy!) site, they might do. Could be done on a lathe. Or, you may want to look into modifying the wheels instead of the gearboxes.