Micro switching guide:

So… you’ve decided you want to build a robot, learnt how they work, read up on the rules, maybe even attended an event. As you sit down to think about your first design, you realise a major flaw... Most of the parts for your featherweight are easy to get, and cheap. Save the speed controller, a key component in your combat robot. A quick browse through the net and you find the cheapest you can get is about $315 Aus! But don’t despair, there’s hope.

Although an ESC (electronic speed controller) would be the best and safest choice for your bot, micro switching is a tried and true method of driving your bot for minimal cost. It’s not that bad either. In Australia, micro driven bots are still compeditive, the 2004 NSW series was won by “Sorry”, a servo switching robot!

What is micro switching/servo switching?
Micro switching involves using a standard radio control servo to acuate two micro switches on each side of the servo using a servo horn. These two micro switches are connected in an H bridge format to the battery(s) and motor(s), and incorporates forward, reverse and brake. One servo switching setup controls one motor, so using the standard two drive motors in a tank steering format, two servos and two separate H bridges will be needed (however there are variations allowing you to drive multiple motors using the one servo, more on that later).

If it’s so good why doesn’t everyone use it?
This method of bot control, while fairly decent, has a fair amount of disadvantages, which is why they are placed lower in desirability to ESC’s:
• They lack proportionate control, making driving somewhat hard (each motor can only be either off or full on)
• No “mixing” is included. This means you either buy a tank or plane style mixer, or drive your bot using tank steering. Most people find due to the subtle inaccuracies caused by mixing that it is unsuited to micro switching. Tank steering gets the best results, but is hard to master and needs a lot of driving practice.
• MICRO SWITCHING LACKS FAILSAFING!!!
Although your standard 12v duel drill driven wedge is semi ok if it goes out of control, if you intend to have a bot with a weapon it is absolutely nesisary that you either buy n ESC, or fabricate some kind of failsafe using a bought failsafe module (such as setting it up to trigger a “kill switch” with another servo. I’ve seen an out of control bot weapon flailing… its not a fun experience and could be potentially deadly, not to mention how embarrassing it is (oh, and you’ll probably get disqualified too).

However this control setup is perfect for beginners. If you can afford to build a bot with a deadly weapon, you could probably afford an electric speed controller too couldn’t you?

Ah that’s the intro done… now to build one eh?

Parts list
(assuming for a 12v duel cordless drill drive featherweight or smaller):

• 4 x 10A minimum micro switches. 5A switches will weld contacts and be permanently on, causing hell to your batteries. If you can find 15A or 20A switches you’ll have no problems with welding at all at 12v with drills.
• 2 x standard size hobby servo’s (free if they came with your radio system)
• A sheet of either thin polycarbonate (3mm works really well) or plastic. Basically you need something for the whole setup to sit on. People have used many other materials too. Try to avoid Perspex; it will crack easily so is very hard to work with.
• 4 x small long bolts to mount the micro switches. They need to be thin enough to pass through the mounting holes in the switch. You will also need a packet of nuts to suit the bolt chosen to raise the micro so it aligns with the servo horn.
• Mounting bolts for the corners to mount the switch setup, however if your lazy you can usually get away with just sticking down the base of the servo and packing them tightly into the robot (make sure there’s clearance for the servo horn to move freely).
• Decent gauge wire. You can get away with 10A but 20A is recommended. In red and black to identify polarity.

Assuming you already had servos, the above setup can cost as low as $10 or if you buy all the gear from jaycar/dicksmith it could cost a fair bit more… but either way, it’s cheaper than an ESC!

MORE TO COME VERY SOON…..