Hello! I am trying to locate an article that appeared sometime in the eighties about building a handheld throttle using items from Radio Shack. It was a simple tethered throttle with a transistor, speed control, reversing switch, and, I think, a resistor or two. The article was either in MR or RMC. I’ve searched the article database but can’t tell just from the title which one I’m looking for.
I was hoping someone might know the article title from my description.
Thanks!
Bob Mitchell
Here are some possibilities.
http://index.mrmag.com/tm.exe?opt=S&cmdtext=THROTTLE+MR&sort=A&output=3&view=25
http://index.mrmag.com/tm.exe?opt=S&cmdtext=THROTTLE&MAG=RMC&output=3&sort=A
I might have the magazine but I need a more accurate month/year/
Rich
Rich
This was an era for a lot of DIY electronics articles. I built several memory walk around throttles for our train club about that time from a Model Railroader Article. This one featured the actual throttle unit under the layout and hand held controllers that could be unplugged and moved to another outlet without stopping the train. Some of them were removed to put in DCC and they promptly came home with me and are under my layout.
Hi Rich - After looking over the links you supplied, I may have narrowed down the article. I know now it must have been in MR as they always would list Radio Shack parts where possible. The throttle was constructed using a small metal box and had a transistor mounter on the outside of the box with a heat sink. It may have been in one of these three articles:
Easy to Build Electronic Throttle, December 1986
Electronic Symposium: Easy to Build Throttle, May, 1987
Build an Inexpensive Walkaround Throttle, January 1986
Thanks!
Regards,
Bob Mitchell
Only problem - good luck finding the required parts at Radio Shack these days. They’re now little more than a cell phone store. If you figure out which of those articles is the one you are tryign to build, I can find equivalent parts at a place like Mouser. Radio Shack’s potentiometers were always kind of junky anyway - huge dead zone off the lower end. I made a quicky jump port throttle for my Digitrax Zephyr usign Radio Scrap parts and even that had the issue - had to turn the knob 1/4 of the way before I got any movement.
–Randy
The article was in December, 1986. I still have the article for future reference. I have built two of them, one from scratch the other from parts from a flea market. They both work great and are virtually indestructible. Smooth control and very inexpensive. And yes, radio shack does not sell these parts any more. I took the atricle to an electronics specialty shop and they fixed me up with all of the parts needed. I am not an electronic geek (still using Atlas selectors, but hey, they work for me at this time), so this is a very doable project. Mine have been in service now for over three years without any problems what so ever. Good Luck!
I designed a simple one back in the late 70’s when I was in high school and I just checked and Radio Shack still sells the parts. The concept was simply a high impeadance JFET linear op amp configured as a voltage follower driving a TIP 120 NPN darlington transistor as the main power circuit. On the input of the op amp was a capacitor. This is where the remote hand held throttle plugged in. The throttle had 4 wires. 2 were +15V and ground. The other two were the center tap of a pot which was the speed control and the other was a switch contact for a toggle switch that controlled a relay for directional control. When the hand held throttle was unplugged from input to be moved to the next walk around plug-in point, the capacitor would hold the charge voltage which kept the train moving at a constant speed until you plugged back in. I also had an emergency stop button which simply shorted the pot center tap to ground to stop the train. It was a pretty simple and straightforward design. No momentum controls or pulse circuits. They could be added but that would i
In February 1995 Mainline Modeler magazine had an article with included schematics for the “Cooler Crawler High-Performance Throttle” designed by Rich Weyand, Bill Pistello and Bill Reid.
You can still acquire this product from TracTronics, Incorporated at http://www.tractronics.com
We use it on our HO scale club layout and it has been very reliable, though few members run DC block control any more.
I looked at the scheamtic and it is very similar to the one I designed. The author used back to back darlington transistor to achieve the high gain necessary to allow the throttle to be unplugged and not discharge the capacitor C1. I used a JFET linear op amp instead of Q1/Q2. The one question I Is the directional latching in the reverse direction. It seems like with R5 feeding the relay that if you have the direction on the handheld throttle set in reverse and then unplug the throttle, R5 will latch it back to the forward direction. At least that is how I am reading the circuit. I solved this by using the other half of the dual op amp and having it drive the direction relay.
Was it this one?
There is no problem with the relay holding its position and the speed remaining constant when the hand held throttle is disconnected. Trains will remain at the last setting of speed and direction until changed by the user.
Notice they recommend getting the potentiometer from Jameco. Wonder why. [:D] [:D] [:D] [:D] [:D]
–Randy
Ths is just a simple designed variable voltage circuit to hang off an existing power supply. There is nothing to hold the voltage constant when you unplug it so the trains would stop. of course you could use a long cord. Also with just a 2N3055 transistor, it will be severly limited by the gain of the transistor and the limited amount of current through the bse of the transistor. I have one of these on my bench I use for DC testing but I would substitute the transistor with a TIP 120 darlington from Radio Shack.
I have built two of these throttles. Both worked well until being replaced by a DCC system just over a year ago. They were easy to build and rugged enough to be used by my two kids when they were little. A drop to the floor didn’t seem to bother them.
John
Yes, Roger, that’s it! Thanks a lot for posting that and thanks to all the others who posted. I would like to (finally!) plan a layout. I have so many locomotives that going DCC would be way too expensive now. From reading MR, one would think that DCC is the only method used.
I had built two of these a long time ago and they worked very well.
Thanks, guys!
RH:
That’s actually why they used the CMU1021 pot, which is rated at 2W. At 12v, the base resistor passes .12 amps. That transistor has a gain of around 20-70, so that’s enough to control at least 2.4 amps. However, those .12A will also have to pass through the pot, which at 12v gives 1.44 W, which is well above the 1/4 watt rating of the Rat Shack pots.
The TIP120 will work, and if the base resistor is upped to 1K, for example, the power dissipated in the pot will be about 144 mW, so a 1/4W pot will be okay. I built a TIP120 into an old Ampack, and it works really well, but it runs pretty close to smoking out from heat dissipation. I discovered this when I decided to smoke-test it with 6 locomotives at once, two of them old Mantuas and one of them an old Athearn.
I need a bigger heat sink or perhaps a few more synapses.
I didn’t actually got look-up the wattage rating of the pot but 2W is sufficient. The maximum power power point for the pot is towards the maximum wiper position but not when the wiper is on full. At that point it has to dissipate the power across the end terminals or .14W (for a 1k pot assuming 12V). The center wiper
[quote user=“jbinkley60”]
I didn’t actually got look-up the wattage rating of the pot but 2W is sufficient. The maximum power power point for the pot is towards the maximum wiper position but not when the wiper is on full. At that point it has to dissipate the power across the end terminals or .14W (for a 1k pot assuming 12V
Hi there,
first time posting on here.
Lately, i’ve been attepmting this throttle as a friend was building me one but that was 6 months ago and i’m still waiting!!@!$^%$^@!
Anyways, i’ve had two attempts, the first one was wrong by a long way, but on the second one, another mate of mine and myself got it working!
The only problem is that the loco would only crawl on the tracks, checked it with the multimeter and it was putting out 11-13 volts, just not much movement on the tracks.
Anyways, i decided to bite the bullet, and i cut the resistor out. and boom! lots of power 
but soon enough the potentiometer was smoking, so i’m guessing thats no good anymore.
I’m using a 1K potentiometer, 1N4007 diode and 100k? resistor.
The only thing my friend has come up with is the transistor (2N3055) or maybe the DPDT switch.
ps. i’m not an expert at electronics at the best of time so english please [:D]
Kind Regards, Brodie
It is not what you think. There are two kinds of potentiometers available. There is the linear taper, and the other is an audio taper. The audio taper is also known as a logarithmic taper.
If you use an audio taper in an application meant for a linear one, the results will be interesting to say the least. The only way to tell the difference (outside of part numbers) is to measure the resistance as the wiper travels along the resistor.
Another reason not to recommend RS as a source is that they may not carry one in that range…