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Step 3Robot Building Tips and Tricks
After building 18 robots, here are some of the things I have learned the hard way.
Separate Power Supplies
If you have the space, you will save yourself a lot of trouble if you use separate power supplies for the microcontroller and its circuits and the motors. The fluctuating voltage and electrical noise that the motors produce can wreak havoc with the microcontroller and sensor inputs to produce very inconsistent responses in your robot.
Trouble Shooting
I find it best to first build the complete circuit of the robot on a breadboard. Components rarely fail or are defective. If your design is valid, and the circuit does not work, it is almost always a mistake in your wiring. For information on how to do fast circuit prototyping, see here: http://www.inklesspress.com/fast_circuits.htm
I then mount all the motors and sensors on the robot body and program the microcontroller to control them. Only after everything is working well, do I try and make a permanent soldered version of the circuit. I then test this while it is still separate from the robot body. If that works, I then mount it permanently onto the robot. If it stops working, it is often the fault of noise problems.
Noise Problems
One of the biggest problems I have encountered is electrical noise that renders a circuit useless. This is often caused by the electrical or magnetic noise that can emanate from DC motors. This noise can overwhelm the sensor inputs and even the microcontroller. To solve this, you can make sure the motors and the wires to them, are not close to any input lines going to your microcontroller.
Pic 7 shows Sparky, R-12, a robot I made that uses a basic Stamp 2 as the microcontroller. I first tested it with the main circuit board away from the robot and after doing the basic programming, everything worked fine. When I mounted it right above the motors, it went crazy and was totally inconsistent. I tried adding a grounded copper clad board between the motors and circuit but that made no difference. I eventually had to physically raise the circuit 3/4" (see blue arrows) before the robot would work again.
Another common source of devastating noise in small robots can be pulsating signals. If you send PWM signals to servos or motors, the wires can act like antennas and send signals that can confuse your input lines. To avoid this, keep microcontroller input and output wires separated as much as possible. Also keep wires carrying power to motors away from input lines.
Magnet Wire
The problem of wire thickness in very small circuits can be solved by using 30-36 gauge magnet wire. I've used 36 gauge wire for some projects, but found it so wispy, it was hard to strip and use. A good compromise is 30 gauge magnet wire. Regular magnet wire can be used, but I prefer the heat strippable magnet wire. This wire has a coating that can be stripped by merely soldering it with enough heat to melt the insulation. It takes up to 10 seconds to strip the coating while soldering. For some delicate components such as soldering to LEDs or ICs, this can be a damaging heat.
The best compromise for me, is to use this heat strippable magnet wire, but strip it somewhat first. I first take a sharp knife and slide it across the magnet wire to peal off the coating and then rotate the wire around until it is stripped fairly well around its diameter. Then I solder the stripped wire end until it is well tinned. Then, you can solder it quickly to any delicate component with less chance of heat damage.
Thin Solder
When components are very close together, it can be difficult to solder them without blobbing over and shorting nearby pads and wires. The best solution is to use a small tipped adjustable heat soldering iron (1/32") and the thinnest solder you can find. Standard solder is usually .032" in diameter which works fine for most things. Using thinner .015" diameter solder allows you to easily control the amount of solder on the joint. If you use the least amount of solder necessary, it not only takes up the smallest volume, but it also allows you to solder a joint as quickly as possible. This reduces the chance of overheating and damaging delicate components like ICs and surface mount LEDs.
Surface Mount Components
Surface mount components are the ultimate in miniaturization. To use SOIC sized ICs I usually use thin solder and magnet wire. To see a fairly easy way to make SOIC breakout boards or circuits see here: http://www.inklesspress.com/robot_surface_mount.htm
Gluing on Components Instead of Soldering
Some surface mount components can also be directly glued onto circuit boards. You can make your own conductive glue and use it to glue on LEDs and ICs. See: http://www.instructables.com/id/Make-Conductive-Glue-and-Glue-a-Circuit/
While this works, it can be somewhat difficult because capillary action tends to wick the conductive glue under the surface mount LEDs and other components and short them.
Gluing On Components Using Non-Conductive Glue
I have been recently experimenting with gluing on components onto copper circuits boards and conductive fabrics using glue that does not conduct.
See Pic 8 for a picture of a 12 volt light bar (unlit and lit) using surface mount LEDs that were glued on with non-conductive glue. I discovered that if you put a thin film of clear nail polish on the copper traces and then physically clamp on the LED and let it dry for 24 hours, you will be left with a good mechanical joint that is electrically conductive. The nail polish glue effectively shrinks and clamps the led contacts to the copper traces forming a good mechanical connection. It must be clamped for the full 24 hours. After that, you can test it for conductivity. If it lights up, you can then add the second layer of glue. For the second layer I use a clear contact cement such as Welders or Goop. This thicker glue surrounds the components and also shrinks as it dries to securely insure a good solid connection to the copper traces. Wait 24 hours for it to dry before testing again.
Being dubious about how long it would last, I left the blue LED light bar in Pic 8 on for seven days and nights. The resistance of the circuit actually decreased over time. Months later, the bar still fully lights with no evidence of increased resistance. Using this method, I have successfully glued very small surface mount LEDs--0805-- size and larger onto copper clad perfboard. This technique shows some promise in making really small circuits, LED displays and robots.
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no money this month.
http://www.instructables.com/id/12-Volt-Battery-Hack!-You_ll-be-Surprised.../
You can get several 1.5s for very cheap, and they appear to be thinner than the one's you're using, so maybe you can fit seperate power sources.
The pictures don't show it too well, but these little guys are like 1/8 of an inch thick. Easy to get at Walmart.