I am currently using an MRC Tech II DC controller for my layout, but I am getting frustrated with having to reach over to the controller to start or stop things as I do switching etcetera along my shelf layout’s 15+ foot length. I want a handheld controller so I can just walk along the layout with throttle in hand. I’d prefer not to replace my current controller, as it is pretty nice (includes momentum and brake controls) and I’m a wicked cheapskate.
My idea is this: I want to build a handheld controller. So far, I assume the parts in question I’ll need will be:
Cheap Radio Shack project box
Some 4-conductor wire
DPDT switch
Potentiometer for speed control
The 4-conductor wire will run to and from the controller–one end will connect to my current DC controller’s output, the other end to my main power bus. I know how to wire the DPDT switch for directional control.
The question is the potentiometer. I want to just crank up the pot on my controller to maximum power, and use another pot on the handheld controller for speed control. What rating of potentiometer should I use for the handheld controller?
I’m not very skilled in electronics, but can generally correctly identify one end of a soldering iron from the other two times out of three–any other factors or considerations for this sort of project?
That won’t work for the simple reason that a potentiometer can’t handle the amperage and voltage that is on the track. The pot that is in the Tech II is controlling a transistorized regulator circuit that sends very minimal current through the pot. You would need a power rheostat for what you want to do, and they can be hard to find and more expensive than replacing your Mark II with a completely new walk-around throttle system. A 25 Watt rheostat, for example, is priced at around $28 or $29 without a knob and dial, plus shipping.
When radio and TV sets still used vacuum tubes, you could purchase wire-wound potentiometers that could handle a heavy load, but with everything today being integrated circuits of very low voltages Radio Shack no longer carries wire-wound pots.
After you add in all of the other parts you would need, you have the cost of a pre-made walk-around throttle from the likes of Dallee Electronics and you haven’t run the risk of burning yourself with the soldering iron.
there have been numerous articles is MR regarding building your own handheld throttle…will see if I can locate one. Then all you would have to do is install a DP/DT switch to switch your layout buss from one throttle to the other.
As Cacole said, you need a better voltage controller than just a potentiometer with today’s low current motors. There are numerous circuits available - I built one myself years ago that I run off the accessory terminals of a cheap trainset power pack.
Using the DC terminals of the power pack, leaving the rectifier out of the circuit, and the power pack voltage turned up, is an option, as you pointed out - and a trap! The primary danger of using the DC output is accidently throwing the direction switch at the power pack, thereby reversing the feed polarity to the electronics in your walk-around controller. The other (occasional) problem with using a DC feed is that some circuits need the 60 cycle AC signal to generate pulses or timing or similar.
The biggest hassle to a walk-around controller is finding a 4 wire plug system that you can enjoy using - I’ve searched in vain to find a reasonable (read inexpensive) way to use just 3 wires so I could use 1/4 inch (the big, not the miniature ones) stereo microphone jacks and plugs. I’ve yet to find a 4 wire plug/jack system that has as good a feel to it. For 4 wires or less use the spiral coiled telephone handset cords - they are a lot less cumbersome then a long, limp 4 wire cord.
I quit using hand made electronics…even those featured in popular books and magazines…everyone of them that i hand built in the past (except for linn wescott’s Twin “T”) bit the dust prematurely…there’s always that part you can’t find and some of them never worked at all after they were built when putting the power to them…I now stick with pre-made electronic circuits from reprutible companies…I use the DALLEE hand held throttle as an example …it’s easy to wire and i don’t have to do all those math calculations to find out the amp, voltage, watt ratings and so forth of the parts…chuck
Switchcraft makes a 3-7 pin series XLR type connector both in “in-line” & panel mount versions If you want a 4 pin in-line female it would be part # A4F male counterpart A4M …panel mount versions D4F & D4M If you need diff number of pins…change the number in the part number ( 5 pin male…A5M) These connectors are available in both black & brushed metal The 3 pin version is what is used on pro type microphones. The 4 pin version is widely used by headset manufactures on commication type headsets. (Clear-Com, TELEX, or Production Intercom) These should be available through Mouser Electronics …One advantage of XLR tyype connectors is that they “lock” together …you have to push a release device on the female connector to unplug