Brushless Direct Drive?

[Giles]

Firstly, Hello, this is my first post on these forums!

*EDIT* I just realised I posted this in featherweight, not beetleweight. Hopefully the question/aswers are still applicable *EDIT*

I'm very new to this, and I am currently working on a beetleweight robot using what little knowledge and parts I have. I have several brushless outrunner motors which I am hoping to use on my robot for a spinning weapon (belt driven) and as the two main drive motors. I have read in a few places that brushless drive motors are considered experimental and are not commonly used for drive. Would it be possible to still use them as drive motors in my bot? Would they need gearing or can they just be ran at a lower speed (as I have read that brushless outrunners can maintain high torque at low speeds).

If the overall advice is to avoid using brushless drive motors, could anybody suggest a good alternative brushed motor setup? I am looking to make a bot that doesn't break the bank but also one that isn't going to fall into pieces when I turn it on!

I have tried to do some reading up on this subject before posting here, but honestly, a lot of the terms and calculations are going over my head, maybe I'm just looking at the wrong info...

Any light that can be shed on the subject would be greatly appreciated!

[maddox10]

Lets calculate. End speed , on the low end is 15 kph.
Affordable brushless speedo's go to 3S. So working voltage is 11.1V.
Normal, small wheel size is 70mm.
For 15kph the wheel needs 1100 rpm. Meaning you need an outrunner with 100KV. That's in the 80mm sizeclass. Not cheap.
In short, you'll need gearing.

My experiments with brushless are not conclusive. In our 6kg raptor Nebelwerfer it's a useable drive. In Hannibalito 3, a feather the same drive, but with larger motors wasn't a succes. Both used a 24-1 gearratio and 120mm wheels.

In Caliope, another feather, it was an utter failure. But that was a 6-1 gearratio and 95mm wheels.

[john_frizell]

Electric screwdrivers make good drives for Beatles. They are definitely at the low end, if you spend more you can get more powerful units that weigh less [I'm sure others will point you to them] and will give you a better machine. But they are cheap when new and you can sometimes get them free or for 50p at a boot fair when their battery packs will no longer hold a charge. They are a good way to get started in Beatles.