Drive motor options

[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!

[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

[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.

[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

[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]

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]

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

[maddox10]

As low as needed, but each stage adds weight, complexity and size.

It also depends on what gear-ring you have available.

[Eventorizon]

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

He recently put this info up (Directly and indirectly)...

ESCs: Trackstar 80A brushless car controlers

Motors: NTM Prop Drive 42-38 750Kv (Picture matched and found here: http://www.hobbyking.com/hobbyking/s...arehouse_.html)

Reduction: 10:1

Wheel Dia: 102mm (Taken from ebay. Same width, hex and scale so I am assuming the OD matches too. http://www.ebay.com/itm/4PCS-17mm-Hu...-/360669106232

Provided the ESC's work off the shelf, this should be easy enough to reproduce and modify. I have to say that guy has some serious skills. Check the 43rd page, all those designs!

Or here: http://i34.photobucket.com/albums/d1...psba4b0087.jpg

[leorcc]

We are testing with brushless drive as well but in a lower weightclass. Still there is no reason to assume the drive will be any different with the larger ones than the results we've had with the smaller ones. One thing about the Trackstar ESC's, the programming card is quite useful but one of the settings is not available on that card. You would need to use the transmitter programming option for that.

[Ellis]

States on the thread that the wheels are 100mm. Believe that ESC is rated for just 3s, so at 10:1, that's 10mph top speed. Over 1hp potential drive power. Pretty nice, and as per the video, drives quite nicely. Doesn't quite look like 10mph, though. Might be running 2s.

Either way, it proves the point that it's viable. Just for high power drives, the speedos are behind a bit.

That said, I believe the American machine "Hot Stuff" (a 60lber) uses brushless drive, too. Very powerful. No idea on actual specs, but it's running some Turnigy Trackstar motors into Dewalt gearboxes, and cheapo Chinese motor controllers. Might be worth trying to find out more. There are several videos on the builder's channel of tests: http://www.youtube.com/user/dtrobotics/videos

[Liftoff]

Does it make any difference if you use an unsensored motor on a sensored esc?

[Ellis]

You have to match them. Sensored motor needs a sensored speedo, and vice-versa.

[plargen]

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

if you look further back he also made this
https://www.youtube.com/watch?v=bRkM_OzetfM

[Liftoff]

Wouldn't this esc be better suited to those brushless motors? Its unsensored, like the motors are, and it can take up to 6s lipo if I understood correctly....reading through the feedfack on this esc one guy mentioned that it can also control a brushed motor... don't know if it's possible at all.
http://hobbyking.com/hobbyking/store...s_Car_ESC.html

I'm really tempted