Implementation of Cooler Crawler Throttle for model railroading

boardless component layout

Component layout for soldering. Component not to scale. Modified to suit available parts.

Schematic of rotary knob hand unit and pushbutton hand unit
Table 1. CoolerCrawler Throttle Base Unit Parts List
Part Value Part number
Relay 12V 4PDT Radio Shack 275-214
Transistors Q1, Q2 2N3904 Radio Shack 276 2016
Transistor Q3 TIP120 Radio Shack 275-2068
Transistor Q4 2N3055 Radio Shack 276-2041
Heat Sink for Q4 TO-3 Heat Sink Digi-Key HS103-1.25-ND or HS110-3-ND, or Mouser567-HP1-TO3-CB
Diode Bridge DB1 4A 50V Bridge Rectifier Radio Shack 276-1146
Diodes D1, D2, D3 1N4001 1A Rectifier Diode Radio Shack 276-1653
Diode D4 4.3 Volt 1W Zener Diode Radio Shack 276-565
Capacitors C1, C2 1,000 uF 35V Axial Electrolytic Radio Shack 272-1047
Resistor R1 56 KOhm 1/4W Radio Shack 271-1342
Resistor R2 220 Ohm 1/4W Radio Shack 271-015
Resistor R3 1 Ohm 10W Radio Shack 271-131
Resistor R4 1 KOhm 1/2W Radio Shack 271-023
Resistor R5 330 Ohm 1/2W Radio Shack 271-017
Table 2. CoolerCrawler Throttle Base Unit Pinouts
Pad # Designation Description
1 SPD Speed Control Lead to Hand Unit
2 XFMR1 Transformer Lead
3 XFMR2 Transformer Lead
4 Dir Direction Lead to Hand Unit
5 GND Ground Lead to Hand Unit/Reverse Loop Ground Rail
6 Common Rail Common Rail Lead to Track
7 Hot Rail Hot Rail Lead to Block Controls
8 POS Power Lead to Hand Unit
9 Meter1 Ammeter Minus Lead / Reverse Loop Hot Rail
10 Meter2 Ammeter Plus Lead
Rotary Knob Hand Unit Parts List
Part Value Radio Shack
Resistor R1 1000 KOhm Trim pot 271-284
Resistor R2 5 KOhm Pot 271-1714
Resistor R3 47 KOhm Trim Pot 271-283
Resistor R4, R5 10 Ohm 1/2W 271-001
Resistor R6 1 KOhm 1/4W 271-1321
Push-buttons Momentary NO 271-609, 275-618, or 275-1566
Pushbutton Hand Unit Parts List
Part Value Radio Shack
Resistor R1 15 KOhm 271-1337
Resistor R2 2.2 KOhm 271-1325
Resistor R3 10 Ohm 1/2W 271-001
Push-buttons Momentary NO 275-609, 275-618, or 275-1566

Original design plans, schematic, and component list by Rich Weyand. The original image has been crudely butchered into the above image and four tables.


The magic is the way this circuit puts 'bumps' into the power supplied to the track. The idea is to jolt the motor at low rpm so it can crawl on the track.

getting ready for assembly

Must've spent like a week working out the layout on paper before I put the things together.

Dud switches

Those nice looking, nice feeling momentary push switches I got at Mike Quinn's just didn't work.

Bad switch installed

Didn't know until they were installed and had to remove hem and replace with Radio Shack ones.


The next thing that sucked was the realy that does the reversing, they tended to stick ,return spring was not strong enough compared to the coil.

Bad component choices

A bunch of bad component choices, like, not getting the right camp can be solved by ganging up a bunch of them together, right? That's what the text book said, but in real life its a nightmare. The heat sink is just a tea candle cup. Couple that with the bad switches and nothing works.

Bad choices

A few more bucks of investment later... a power supply that works.

finished product
orange blue green blue green orange cyan green

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