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This page describes the Orb Motor Controller (ORBMC). It is a customized version of the Open-Source Motor Controller, and as such we are releasing the design, schematic and PCB layout for anyone to use or modify.


You will need:

  • fine-pitch solder, preferably lead-free
  • A soldering iron (heat controlled with a fine cone tip is best)
  • an exacto or utility knife (to cut SMD parts out of carriers)
  • Tweezers or fine needle-nose pliers
  • Diagonal or similar wire cutters (to trim leads)
  • Old toothbrush and denatured alcohol (to remove solder flux)

How to Solder SMD Components

SMD stands for "surface mount device" -- they are small components that instead of wire leads have solder pads. They sit on top of the printed circuit board, and the trick is to solder them to two small rectangular pads where they sit. It's an easy 4-step process:

1. Put a small dot of solder on one of the two pads. Melt it so it is a smooth bump. 2. Using a tweezer or similar tool, place the SMD device between the two pads. Melt the solder bump while holding it in place (otherwise surface tension will drag it away. 3. When the solder cools the device will be fixed in place. Solder the other pad. 4. Go back to the first pad and add a little more solder if necessary.

Assembling the ORBMC Printed Circuit Board

Component names and orientations are printed on the "silkscreen" -- the white markings on the top side of the printed circuit board.

1. Install 8 150 ohm gate resistors R3-R9 + R14. These are small surface mount resistors marked "151" (15 x 10^1 = 150).

2. Install R10 and R11. These are 220K ohm small surface mount resistors marked "224" (22 x 10^4 = 220,000).

3. Install R1 (it's near D1), a 14K resistor marked 1402 (0r a 15K).

4. Install 3 1K input protection resistors R12, R13, R15. These are marked 103. In the rev0 board, be careful not to get a solder bridge to the via (hole) near R13.

X5. Install a 680 ohm dropping resistor R2. It's near the LEDs on the other end of the board.

6. Install 5 1.0 uF bypass capacitors C1, C2, C6, C7 and C8. These are unmarked surface-mount brown rectangles.

7. Install 8 Schottky diodes SD1-SD8. They are marked "S1." The polarity is important: make sure the white bar (not the "1") is in the same direction as the white rectangle on the PCB silkscreen.

X8. Install the red and green indicator LEDs. LED1 is green, LED2 is red. Polarity is important: make sure the green bar goes in the direction of the white dots on the PCB silkscreen.

9. Install the 33uF bypass capacitor C18. This is the orange largish surface-mount block. The polarity is important: make sure the bar on then end is installed in the + direction.

OK, it may not seem like it, but you are more than 1/2 done. D3-D5 and D12-D16 are optional on this board and we are skipping them. At this point, it's a good idea to remove the solder flux (brown resin) from the top of the board. Using a toothbrush saturated in denatured alcohol (99% rubbing alcohol works great), scrub the board and repeat until no longer sticky or dull.

10. Install the protection diodes D1 and D12.Polarity is important: make sure the white bar goes the same direction as the silkscreen image.If you have a lead bender, bend for .6 lead spacing.

11. Install the FET driver IC2. Polarity is important: make sure the notch or dimple on the IC matches the silkscreen.

12. Install the resistor pack RN1. Polarity is important: make sure the dot on the resistor pack is at the same end as the "1" on the silkscreen.

Now is a good time to turn up the heat on your soldering iron if it is controllable. We will be soldering to the ground plane which can soak up a lot of heat.

13. Install the 3 transient voltage suppressors D6, D7 and D15. Polarity does not matter; ignore the white bar on the silkscreen. If you have a lead bender, bend for .6 lead spacing. D6 and D15 are very close: insert them both before sodlering so they can snuggle together. In the rev0 board, D6's cathode is too close to an area of exposed ground plane. Make sure this has been masked before soldering.

14. Install the 10-pin header SV2.

15. Install 8 power MOSFETs. Ensure the metal tab matches the silkscreen. Make sure they don't slide out when you tunr the board upside down to solder it. I solder the gate (pin closest to the dot) then check that they are still seated, then solder the other two pins. Run extra solder along the exposed traces on the TOP side of the board.

16. Install three bypass capacitors C3, C4 and C9 (you can skip C5). Polarity is important: make sure the negative side (with the stripe on the case) does not go into the hole labeled "+".

17. Once everything has been soldered, run extra solder along the exposed traces on the top and bottom. Be liberal but neat: this is to increase the ability of the board to conduct current. Take care not to bridge any solder onto other connections or over the wire holes. After this you will need to clean the board again to remove flux.

Congratulations! You are done. Roll on!

Installing the ORBMC in the Enclosure

H-bridge wiring

There is a 12-pin header labeled SV3 arranged as rows of 6 pins each.

it looks like

2 4 6 8 10 12

1 3 5 7 9 11

Only pins 1 and 12 are numbered. It will look upside-down to you with the board end closest to you.

Adjacent pins are connected so there are only 6 connections. Wire as follows:

Pin 12: RED

Pin 10: BROWN


Pin 6: GREEN