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
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
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
Regards,
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
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
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!
rrinker 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
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 increase the complexity and cost.
Engineer Jeff NS Nut Visit my layout at: http://www.thebinks.com/trains/
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.
cacole 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?
Roger Hensley= ECI Railroad - http://madisonrails.railfan.net/eci/eci_new.html == Railroads of Madison County - http://madisonrails.railfan.net/ =
jbinkley60 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 problem by using the other hald of the dual op amp and having it drive the direction relay.
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 problem by using the other hald of the dual op amp and having it drive the direction relay.
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.
rogerhensley Was it this one?
Notice they recommend getting the potentiometer from Jameco. Wonder why.
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!
jbinkley60 rogerhensley Was it this one? 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.
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.
Autobus Prime jbinkley60 rogerhensley Was it this one? 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. 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 would have no resistance thus no power dissipation but would have to pass up to .12A, which is limited by R1. The problem I was pointing out with the beta of the the 2N3055 is the beta is so low that except at maximum throttle you will be limited at how much current it can provide.
Take the example of the throttle at midpoint and assume a linear taper pot (1k ohm in value). The maximum current the the base of the transistor is 12V / 600 ohm = 25ma. With a beta of 20-70 the output current would be .5-1.75A . From my experience the 2N3055 rarely sees a beta of 70 except at certain operating points. So back when this was designed .5-1.75A would drive 1-2 older locomotives. Replace the 2N3055 with a TIP120, which has a beta of at least 1000, the limit would become the collector current, heat sink and source power supply. Now having the small aluminum box be the heat sink, it could get wrm very quickly since at 2A and a 6V output the transistor would be dissapating 12W.
So the 2N3055 will work fine. My only suggestion was a TIP120, which would be a better choice and would allow the use of more readily available smaller wattage pots.
jbinkley60 Autobus Prime jbinkley60 rogerhensley Was it this one? 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. 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 would have no resistance thus no power dissipation but would have to pass up to .12A, which is limited by R1. The problem I was pointing out with the beta of the the 2N3055 is the beta is so low that except at maximum throttle you will be limited at how much current it can provide. Take the example of the throttle at midpoint and assume a linear taper pot (1k ohm in value). The maximum current the the base of the transistor is 12V / 600 ohm = 25ma. With a beta of 20-70 the output current would be .5-1.75A . From my experience the 2N3055 rarely sees a beta of 70 except at certain operating points. So back when this was designed .5-1.75A would drive 1-2 older locomotives. Replace the 2N3055 with a TIP120, which has a beta of at least 1000, the limit would become the collector current, heat sink and source power supply. Now having the small aluminum box be the heat sink, it could get wrm very quickly since at 2A and a 6V output the transistor would be dissapating 12W. So the 2N3055 will work fine. My only suggestion was a TIP120, which would be a better choice and would allow the use of more readily available smaller wattage pots.
jb60:
Whoops! Looks like I screwed up and disregarded the pot's resistance. Posting before thinking again.
You're right. The highest dissipation in the pot is when it's at just over 11V. At this point, about .06A can flow through the 175 ohm resistance (100 ohm + 75 from the pot), dissipating about .30W, and the rest of the pot is dissipating .13W for a total of about .43W...so I was off by about 5x, but it's still more than the 1/4W rating of the Rat Shack parts, so I don't feel like a total chump.
Definitely agreed on the TIP120. Hard to argue when mine works fine; it just needs a bigger heatsink. In fact, my store-bought Railpower 1300 appears to be little more than a Darlington hooked up as a voltage follower, and it gives good control too.
.5A at half throttle does seem about right for 1-2 older locos at 6v, assuming each motor draws about .5A-1A at 12v full slip. It does seem like this throttle limits current more than it should, given the capacity of the transistor used.
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
Kind Regards, Brodie
rrinker Notice they recommend getting the potentiometer from Jameco. Wonder why. --Randy
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...
betamax rrinkerNotice they recommend getting the potentiometer from Jameco. Wonder why. --Randy 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...
rrinkerNotice they recommend getting the potentiometer from Jameco. Wonder why. --Randy
OH no, I'm pretty sure it's for the reason I said. That other circuit needs a 2W pot, which RS did not sell (although WAY back, I think they did - in the 70's!), but the one using a 1/4 ordinary one - back then RS sold both linear and audio taper pots, in a wide range of values (not so many audio tapers). Even though they listed RS part numbers, in many of Keith Gutierrez's circuit articles he mentioned to if possible get the same value from a different source because of the huge dead zone in the RS part. In a LINEAR taper pot. Heck, I slapped together a quick throttle circuit to use as a jump throttle on my Zephyr and just grabbed some bits at RS because I wanted to build it like..NOW, and had the same issue. For at least 1/4 turn there is NO change in the pot, or so little that the output doesn't change. Junk parts, very simply.
I built a similar one back in 1984 from MR, Dec 1977, The Pacematic Throttle. The big difference is a NPN Darlington plastic transistor between the pot wiper and base of the 2N3055. Much smaller current through the control pot. Eventually added a IC for pulse power and modified it for switching with another switch and a resistor or two. Never did draw up the modifications.
I installed two miniature pots to trim the bottom end of the throttle for swithcing and road conditions so there is not so much wasted space on the control pot. I like to tinker. Everything in a 4 X 2 X 2.5 box.
This throttle served very well for a number of years until I went to DCC. A club I belonged to used four of these for many years.
brod13 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 Kind Regards, Brodie
The first thing I'll ask, Brodie, is about taking the voltage reading on the track: was there a locomotive on the track and running at the time you took the reading? To get an acurate voltage reading for the power pack at full throttle, it has to be under load (in this case, running a locomotive). If the current output of the power pack is insufficient to run your locomotive, the voltage will drop greatly when the power pack is at full throttle as compared to reading the output without a load.
If the potentiometer was smoking, it probably is shot. There's an old joke that electronic components are made of smoke. As long as the smoke stays inside, they're OK. If you let the smoke out, they're no good anymore.
Listing the components without any reference to how they're interconnected doesn't tell us much. What are you using for a power source for your throttle?
i just thought that if i listed them they might provide some insight into power going through the circuit or something.
We tried a clipper transformer (a relic), which was 12v, a 12v power pack and a bachmann spectrum controller which has an output of 15v DC.
It was tested with a multimeter, with and without a loco on the track.
Regards, Brodie
Cool. I built two of these throttles in the eighties too, from the same article, and even forgot the source while trying to find at least similar plans. Dug out of a box of junk from a long disassembled layout, they still work great for my revived interest in N scale modeling, and want to build a couple more. How cool that here it is years later. Thanks to all.
rrinker rogerhensley Was it this one? Notice they recommend getting the potentiometer from Jameco. Wonder why. --Randy Hi Everybody, My name is Ian and I just joined this forum specifically to ask if anyone can tell me what year and month of MR the above throttle appeared in. I know this thread is very old but maybe someone will remember it... I'd like to get a copy of the magazine with the original article (although finding the picture answered most of my questions.) I have two of these little throttles that I built years ago. One of them just stopped working and I've spent quite a while trying to track down the actual schematic for it. Unfortunately, all my magazines were given away years ago so all I could do was hunt online. Fortunately, I found this thread without too much trouble. Thanks a lot for your help! Ian
IanMcGoo22 Hi Everybody, My name is Ian and I just joined this forum specifically to ask if anyone can tell me what year and month of MR the above throttle appeared in. I know this thread is very old but maybe someone will remember it... I'd like to get a copy of the magazine with the original article (although finding the picture answered most of my questions.) I have two of these little throttles that I built years ago. One of them just stopped working and I've spent quite a while trying to track down the actual schematic for it. Unfortunately, all my magazines were given away years ago so all I could do was hunt online. Fortunately, I found this thread without too much trouble. Thanks a lot for your help! Ian
Hi Everybody,
Contact Kalmbach (call / email) might be your best bet. I've done it a couple of times in the past for articles from the 50s and 60s, price is pretty reasonable too.
-Dan
Builder of Bowser steam! Railimages Site
December 1986, page 116, article by Al Turner.
Just need to get creative with the search in the 75 year DVD. I searched for Jameco Electronics.
Randy, thank you very much for your help. Now I can get in touch with Kalmbach and buy a back-issue of the magazine. I always intended to contact the company but I figured it would help if I knew the month and year I was looking for.
Best wishes,
Ian
[quote user="mitcher"]
I am writing this post, October 20, 2016. I have found the article that you and others before me have described. It is in the December, 1986 Model Railroader at page 116-117. I have received this article courtesy of a friend. He built one of these some years ago, it worked fine when he sent it to me with a 1.5 amp DC source, but when I tried to put on a 3 amp DC power pack something blew up. I have put the handheld throttle back together and with new components, but when I try to use it although there is a measured 10.4 volts entering the potentiometer, there is no voltage coming from the hand held out to the track! //////////////Can anyone help me get this thing running trains! Mikw Ross, reach me at mike3ross@yahoo.com