Brushless Beetle Drive

[Rapidrory]

I was working on a project for brushless beetle drive motors, but I didn't end up doing anything with it and so am dismantling it for another project. However the set-up worked very nicely and so I felt I'd post the details here in case someone else finds it useful.



Uses one of these brushless
and the gearboxes from the standard beetle motor
Obviously different ratios can be selected; about a 20:1 ratio should give the same output speed as a normal beetle motor..



To fit the two together, I just pulled the cog off the DC motor, and pressed it onto the shaft of the brushless (some loctight wouldn't go amiss to keep the cog tight on the shaft). The shafts are both 2mm, the brushless' one just needs hammering through until it sticks out the back.

Both the brushless and gearbox have multiple mounting holes, so the brushless just bolts straight to the gearbox. And that's pretty much it; only took about 10 mins. Worked really nicely, weighs ~53g; 30g lighter than regular beetle motors, and substantially shorter.

I used a 10A car ESC for mine, but didn't get a programming card so don't know how much it can be reprogrammed. As it was it was fairly unusable.

Apparently these should work well given some reprogramming, though I can't speak from experience.

I hope this is useful to someone...

[harry hills]

https://www.youtube.com/watch?v=74YuKhVN7ik

trackstar escs are amazing. I use different sk3 motors but along the same lines for everything else

[Pinski1]

I'd love to see your setup Harry, got a completely bonkers idea for a beetle that brushless motors could help with.

[harry hills]

Its more or less the same setup but I'll document it sometime when I get the chance.

[Giles]

Is there any distinct advantage to using brushless motors for drive? Im currently building my first beetle weight and I have some brushless motors left over from an old RC project. I'd love to use them in a similar setup, but everything I've read so far has been telling me not to use brushless motors as drive motors?

[harry hills]

It's a bit more complicated and expensive but can work just fine.

[Giles]

Hmm ok. Considering I already have the motors and ESC's it might end up being the cheaper option for me at the moment! Do you know if anywhere sells the gearboxes linked in the original post without the motors? Or do you need to just buy both together?

[Ellis]

Hi Giles. The problem with brushless as drive motors (in any weight class) is the control side. Unsensored motors, which yours will be, need to be in motion for the ESC to have information about how to control it. That basically means that they are awesome once going, but can struggle to get going at all, as the controller has to "guess" what power to send to what phases to make it spin. If the motor is under no load this works fine, it's when it's being held back, say by the inertia of a combat robot, that it may stutter. The generally accepted solution to this is to give the motor plenty of gear reduction, so that it has as much mechanical advantage as possible, ie, so that it doesn't have to fight so hard to spin a wheel. Either that or massively over size it so it doesn't care so much.

The other problem is that brushless motors need to be brought to a total stop before they can change direction. Unlike in brushed where you can just flip polarity and the motor will screech to a halt and go the other way as quickly as it can, a brushless can't do that. This means you need an ESC with the right brain for changing the brushless' direction without a hesitation, and as that's not commonly needed in RC (the world from which what we use originates), those are hard to come by.

Assuming you can get past all that and find a suitable ESC (as Rory/Harry are/have), the benefits are in power density. Brushless RC motors generally blow the socks off brushed motors in power for the same weight. For this reason they can be smaller and lighter for the same grunt. It's just designing a reliable setup to overcome the above that means we're mostly using brushed tech. It's just super simple, super tough, and cheap.

EDIT: I got seriously post-ninjad. Oh well, might still be helpful.

[Giles]

Post ninjad indeed!
Very good info though, thanks a ton. I don't really know much about robotics yet, so finding out the basics is great. It's starting to sound like "you need to know your stuff if this is going to work" In which case, i might be better off buying myself some brushed motors for my first steps into building combat bots

[Rapidrory]

Having just acquired a Lynx which has brushless drive, I've started looking into this again.
The Trackstar 25A ESCs it has seem a little excessive for the relatively small sk3 2118 brushless. Was wondering if something like the Afro 12A (http://www.hobbyking.co.uk/hobbyking...Version_3.html) would be more suitable? Would likely need reflashing with the right version of SimonK but that seems fairly simple, and it's cheaper and smaller than the Trackstars...

[harry hills]

Yes this works and is nicer control than the trackstars.

[Rapidrory]

Good to know. Which version of SimonK is needed to make it suitable for drive, or is there just some settings that need changing? (I am by no means an expert on these things)

This may end up in a very silly antweight version of Nuts..

EDIT: Been looking at gear ratios as I'm possibly adding much larger wheels to lynx; The gearbox for the 1000rpm gearmotors is 14:1, the gearbox for one of those 200rpm gearmotors with the rubbish motors fitted is 44:1... Just in case anyone wanted to work out what KV motor to get...