95 lines
4.8 KiB
HTML
95 lines
4.8 KiB
HTML
<h1>How to build a Y3MD</h1>
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The Y3MD is <a href=http://www.yaaarc.org>Ypsilanti Ann Arbor Area
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Robotics Club</a>'s design for a 3 channel Motor Driver. It acts as an
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H-bridge amplifier, so a small processor like a Basic Stamp or a LEGO Mindstorms
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RCX can drive much larger motors, such as those found in Barbie Ride-On Jeeps.<p>
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Each channel of the motor driver can easily drive a 30 amp, 12 volt motor.
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There are 3 channels, to match the 3 motor outputs on a LEGO Mindstorms RCX.
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The outputs can be run in parallel to drive higher current motors.<p>
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The boards can be cut into 3 sections for individual H bridges.
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<p>
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It is a simple circuit. With no input, the N channel MOSfets are kept
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turned off by the 15k pull up resistors, likewise for the P channel
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MOSfets, except their resistors are wired to pull down. Each LED in
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the optoisolator is coupled to a phototransistor. Each phototransistor
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drives a MOSfet. The LEDs are wired so that 1 pair will be turned on by a
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positive voltage, the other pair will be turned on by a negative voltage.
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It is impossible to turn on both pairs of LEDs at the same time. Which means
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that it is impossible to turn on both pairs of MOSfets at the same time.<p>
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Each P channel MOSfet shares a heatsink with an N channel MOSfet. If
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the circuit is built correctly, it is
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impossible for both MOSfets on a heatsink to be on at the same time.
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I had a bad solder joint on a pullup resistor on the first prototype, which
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was on a circuit board with wimpy little traces.
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Without that pullup resistor, it was possible for both MOSfets to be on
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at the same time. The MOSfets failed and the wimpy traces blew up.
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These circuit boards have very wide traces, so the MOSfets explode without
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damaging the circuit board.
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<p>
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<ol>
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<li> Identify the parts<br>
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<a href=images/allparts.jpg><img src=images/allparts_t.jpg alt=allparts.jpg></a><br>
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<ol>
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<li> 6 <a href=http://www.digikey.com/scripts/dksearch/dksus.dll?PName?Name=HS104-2-ND&site=us>TO-220 PWR CLR 1.45"10W heat sinks</a>
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<li> 9 Connectors 3 power, 3 motor, 3 input.
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<li> 1 Y3MD circuit board
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<li> 6 4-40 nuts
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<li> 6 4-40 .25 inch screws
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<li> 3 <a href=http://www.digikey.com/scripts/dksearch/dksus.dll?PName?Name=PS2501-4-ND&site=us>PS2501-4 4 channel Opto isolators</a>
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<li> 3 1k resistors LED current resistor.
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<li> 12 15k resistors pullup resistors.
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<li> 6 <a
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href=http://www.digikey.com/scripts/dksearch/dksus.dll?PName?Name=IRF4905-ND&site=us>IRF4905,
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55V, 74Amp P channel MOSfet</a> install next to the P on the circuit board.
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<li> 6 <a href=http://www.digikey.com/scripts/dksearch/dksus.dll?PName?Name=IRF1010N-ND&site=us>IRF1010N 55V, 85Amp N channel MOSfet</a> install next to the N on the circuit board.
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</ol>
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<li> mount resistors,<br> component side is the side with words.
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<ol>
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<li> Install the 3, 1K Ohm resistors (current limit for LEDs for optoiso).<br>
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<a href=images/threeresistors.jpg><img src=images/threeresistors_t.jpg alt=threeresistors.jpg></a><br>
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<li> Install the 12, 15K Ohm resistors (pull up or down resistors for MOSfets).
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<br>CAUTION. If you have a bad joint on any one of these resistors,
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the smoke will come out of a P channel MOSfet!
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<b>check those solder joints</b>
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<a href=images/allresistors.jpg><img src=images/allresistors_t.jpg alt=allresistors.jpg></a><br>
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</ol>
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<li> mount the optoisolators
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<br> Pin 1 is the square pad. Upper left corner.<br>
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<a href=images/opto.jpg><img src=images/opto_t.jpg alt=opto.jpg></a><br>
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<a href=images/optocloseup.jpg><img src=images/optocloseup_t.jpg alt=optocloseup.jpg></a><br>
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<br> Insert each chip
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<br> Bend pins on opposite corners of the chips, to hold the chip on when you
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flip the board over to solder.<br>
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<a href=images/optopinsbent.jpg><img src=images/optopinsbent_t.jpg alt=optopinsbent.jpg></a><br>
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<br> Solder them.
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<li> mount connectors. Make sure the openings point out.
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<li> identify and install the MOSfets. <br>
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Note that pairs of MOSfets share a
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<ol>
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<li> IRF4905, P channels go next to the P.
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<li> IRF1010N, N channels go next to the N.
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<br> Screw goes into the hole in the N channel MOSfet.
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<br> Put the N channel and screw onto the heatsink so the threads stick out the bottom of the "U".
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<br> P channel onto the threads.
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<br> Then the nut.<br>
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<a href=images/twomosfets.jpg><img src=images/twomosfets_t.jpg alt=twomosfets.jpg></a><br>
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<br> Repeat for all 6 pairs of MOSfets.
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</ol>
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<li> Solder in the MOSfets.<br>
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<a href=images/connectorsmosfet.jpg><img src=images/connectorsmosfet_t.jpg alt=connectorsmosfet.jpg></a><br>
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<li> Test it with a 1KOhm resistor in series with the power supply. This will provide enough
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current to light an LED, but not enough to blow up a MOSfet.
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</ol>
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Here are George and Erik sorting the parts to make the first 10 kits.<br>
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<a href=images/sortingparts.jpg><img src=images/sortingparts_t.jpg alt=sortingparts.jpg></a><br>
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</html>
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