# Curious Throttle Issue



## East Broad Top (Dec 29, 2007)

Okay, maybe "curious" isn't quite the right word, because I've every belief I know what's happening. The question: is there an elegant solution to mitigate it?

Here's the thing. I've been installing R/C in my EBT mikado. For space/aesthetic considerations, I'm using HiTec micro servos, as I'd rather not clutter the cab with full-sized servos. (More room for a proper crew.) 

Anyway, everythng works great when the loco's cold on the workbench. Heat things up and put 60 pounds of pressure against the throttle, however, and the valve becomes very stiff--stiff enough to where the servo just sits there and says "the loco may think _it_ can, but I ain't gonna bother." 

I can't change the gear ratio, because I need 180-degrees of travel on the throttle, and the servo only rotates about 90 degrees. A larger (standard size) servo would probably give me enough torque (I've got one pumping water into the boiler) but I'd prefer not to use the real estate lest my poor crew no longer fit--and it NEEDS a proper crew. My other thought would be to double up with a second micro servo, since it's a chain drive to the servo. Not quite as much real estate as a standard servo, but how much advantage would that actually give me? 

But what about the throttle itself? Is there something that can be done (easily, not involving replacement) Nothing's coming to the top of my mind, but if anyone has any ideas, I'm definitely open...

Later,

K


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## Michael Glavin (Jan 2, 2009)

Kevin, 

First off, pretty much all servos I'm aware of rotate 60 degrees in either direction for a total travel arc of 120 degrees... 

Your gear ratio maybe a problem as well as mechanical clearances with the throttle needle assembly. As you’re likely aware as things warm clearances tend to shrink, dissimilar metals sometimes exasperate the phenomena. 

What are the diameters or lengths of your servos output arm/sprocket and the driven end too. 

Hitec has micro servos that use digital amplifiers and coreless motors; these are more precise and offer more power in the same physical size. Which model servo are you using? 

Michael


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## steamlogger (Jan 2, 2008)

Have you tried putting a small bit of steam oil on the throttle O ring? 
I get plenty of speed with only about 120 degrees of travel. I put an extended handle on the throttle and it rotates from just touching the pipe to the right burner to the cab roof. The throttle is not tightly closed at off but the engine will not move even with 60 pounds of pressure. With a 12 car train mine will run quite nice by opening the throttle pointing at the edge of the foot plate, and runs very fast with it fully open.


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## David Leech (Dec 9, 2008)

If I understand you, you are saying when cold it works fine - the servo moves the throttle open and closed. 
When 'hot', it won't open it, from the closed position. 
If you 'help' it manually, does it then work okay, or are you saying that it is stiff ALL the time. 
Due to expansion of metals, I guess that I can see how something may be causing it to be stuck from the closed position, but not sure about just stiff. 
Maybe the thread needs a clean? 
All the best, 
David Leech, Delta, Canada


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## Charles M (Jan 2, 2008)

Kevin, 
After watching you run on Wednesday with the throttle problem , have you run the Mike on rollers to see how much throttle it really needs to run ? I have seen that the K-36 only needs the 90 degrees of traviel to run at a very realiistic speed. I did servo mounts for both Joe's K-28 and Ta's K-36 with only 90 degrees of roatation on the throttle and that was plenty. 

Charles M SA # 74


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## Charles M (Jan 2, 2008)

Kevin, I have been using the Hitec HS-82MG servos with good success. The next one up in torque appears to be the HS-225MG servo, with about a third more torque. It is just sliightly bigger in size than the 82 series , it might be possible to shoe horn it into the cab . 

Charles M SA # 74


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## Cougar Rock Rail (Jan 2, 2008)

Kevin, have a look at this line of linear actuators....they may work for you.... 

http://www.firgelli.com/ 

Keith


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## Taperpin (Jan 6, 2008)

Kevin, 
Try removing the throttle screw, clean and apply MOS anti scuffing paste to the threads and O ring ,reinstall, wont "wash out and should fix it.. 

Gordon.


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## East Broad Top (Dec 29, 2007)

It's not sticking, it just gets very stiff to rotate, needing lots of "friendly persuasion" to get the servo to move the throttle. I thought about changing the ratio, because on the flat I seldom run at more than 60 degrees throttle from closed. But that's on the flat. My home railroad has steeper grades and tighter curves, and I know from running my other locos that I've got to give the locos a good hit of steam to get moving on the grades, then back off. I want to make sure I have the ability to give it the steam when it needs it. (Charles, the good news is that pinning the sprocket on the throttle worked great!) 

Upon coming home, I found a surplus standard-sized servo, and determined I could fit it inside the cab without violating the sight lines in the cab windows. (Thank goodness for high roof arches). I think I'm going to go that route and see what that gets me. I've just got to figure out how to build the mount. If that still gives me fits, I'll replace the sprocket on the throttle for a 1:1 ratio, and hopefully between that and the beefier servo, I'll finally have control. 

Oddly, my Johnson bar servo gets to sticking every now and then, too, when moving out of neutral. If it's in forward, I can drop it to reverse and vice versa, but if I move to neutral, it sometimes hangs up. Then once I move it up or down and back into neutral, then I can move it back out of neutral again. Everything's lubed and moving freely so far as I can tell. Hopefully if I get this throttle issue resolved, I won't have to use the Johsnson bar to control my speed and stop, so it will spend most of its time either in forward or reverse. (Besides, slopping the water over the bulkhead into the R/C section is probably not the best thing to do...) 

Later, 

K


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## Tom Burns (May 11, 2008)

Kevin,

One very easy trick to try. Assuming you are using the typical 4.8V reciever batttery pack, try switching with a 6V reciever battery pack. You can check with your local hobby store or online to confirm but most if not all modern RC systems are OK with 6V. You will need a 6V charger unless you are using disposable or have a high end charger the charges anything.

Simply with the additional voltage, you have increased torque by 20%.

If this does not work, go to servocity.com and look for a servo with the highest torque rating for the size you need. Even in the micro size, there is a full range of available torque ratings available for a few more bucks. Unlike airplanes, with trains you do not need to worry about the compromise of torque versus servo speed. You can easily double or tripple the rated torque over a standard micro servo rating that should probably do the trick.

Tom Burns
RGS in Live Steam


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## Dwight Ennis (Jan 2, 2008)

While probably not of much help here, I had a similar problem once caused by side-to-side play in the throttle. When the servo tried to rotate it, it also pulled it sideways, jamming it up. My solution was machining an extension collar which affixed to to the original with a set screw and had an extended close-tolerance hole for the shaft to provide support and keep it centered.


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## lotsasteam (Jan 3, 2008)

Pull the throttle completly out and degrease the whole thing ,make shure the inside part is clean and free of burrs,then relube and it should work !( The assembly lube,if used at all is mostly anything but oil (coming from china) 
Hope it helps! 

Manfred


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## Pete Thornton (Jan 2, 2008)

the valve becomes very stiff 
Kevin, 

Mine doesn't. Let's ask Larry G and Richard J what theirs is like. I think you have a stiff throttle. I had to remove mine a few times while installing the sprocket, so it got some use. Try loosening the threads as suggested above somewhere - lapping them in, so to speak. The threads aren't the sealing area anyway, so there's nothing to lose by making them looser. 
Dwight may be on to something. If you have a big sprocket on the servo trying to move a little one on the shaft, it may be causing binding of the shaft. Does it get stiff if you are turning it manually, without the servo drive?



go to servocity.com and look for a servo with the highest torque rating for the size you need 
I'm using Hitec HS65HB servos and they have no problem turning my Mikado's throttle on my 20:18 sprocket ratio. I found a Hitec HS55 wouldn't turn the throttle on my FWRR/Ruby with a 30:16 sprocket pair - I was trying to make the throttle turn more than 90 degrees. It now has an HS65 and a 20:18 sprocket pair and works fine. 

I'll be surprised if you need more than 90 degrees of travel. On Rog's hills (3,4%) it can start 11 hoppers and a combine with only the rig described above. Lack of steam is the biggest problem - you'll note it wheezes to a halt on the 4% corner grade!! 
_Oh heck - I like my video, so here it is. The hill is the middle section:_


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## Shay Gear Head (Jan 3, 2008)

I've had the experience that Accucraft must use worn-out taps and by running a good one through the threads everything fit and worked fine.


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## East Broad Top (Dec 29, 2007)

I'll definitely pull the valve and lube it. The throttle does have some side-to-side play once opened, so that may also be part of it. None-the-less, the poor micro servo seems to have given its all in its effort to turn the throttle, and will be off to an early retirement. (It now turns twice as slowly as the identical servo that's running the J-bar, and sounds awful doing so.) So it's a new servo regardless, and since I can get the full sized one to fit, I'll just run with that one to start. I like the idea of a bearing on the back wall of the cab, too. Shouldn't be difficult at all to fabricate one. I've got some collars that I can turn to fit. 

Thanks, all, for the suggestions. I got the lights working this morning, my quick-connect for the water line is ready to ship, and my crew is winging its way from the Pacific as I type. (alas, it will not be animated.) I need to get some 1/32" plywood to re-deck the running boards, and then #12 will be about as "finished" as I think I'm going to get her. 

Later, 

K


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## Pete Thornton (Jan 2, 2008)

I can't change the gear ratio, because I need 180-degrees of travel on the throttle, and the servo only rotates about 90 degrees.
If you dig around the Servocity website, you'll find a 'servo doubler', which sets up a servo to operate 180 degrees instead of 90 deg. I also noted the 'digital' servos can be programmed for greater travel if you want them to. 

The mikado is my 4th Accucraft r/c conversion, and all have operated satisfactorily, up hill and down, with just 90 degrees of travel on the throttle and servo.


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## Larry Green (Jan 2, 2008)

Kevin, your micro quick-connect started west yesterday. 

Tom B, if you are reading this, I will have a couple of them with me at CF and DH if you are interested. 

Larry


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## Charles M (Jan 2, 2008)

Kevin, 

One more thought you might look at. If you need more than 90 degrees of travel on the throttle , look at the valve travel with the loco in forward gear. Does the valve rod move the same amount on both the right and left sides of the engine ? Had a K-36 delivered last year that was not adjusted right . The right side had almost no valve movement when in forward gear. Had to reset the eccentric arm and that got it running right. 

Charles M SA # 74


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## East Broad Top (Dec 29, 2007)

The movement past 90-degrees hasn't really been needed except to goose the loco up through tight spots where it just needs that extra shot of steam. (There are a few places on the track at the Museum where this is needed, especially when switching--and I love to do switching.) I've been running the loco on blocks working out the throttle issues, and it's definitely not a timing issue. The loco's very smooth in both forward and reverse. Again--on the flat--I'm rarely more than 60-degrees from closed even with a heavy train behind. Getting started with such a heavy train on 5' radius curves on a 2% grade on my home railroad, I know from running my other locos that getting a big volume of steam behind you in those circumstances is a good thing. So, no, I don't need the full 180 degrees rotation, but I do want more than 90 (or about 105, which is the maximum I can get from the servo with maximum travel programmed into the transmitter and a 1:1 gear ratio.) 

The nice thing about the Dx6i transmitter I'm using is that you can customize the travel of your throttle stick. I've got mine set to where about 80% of stick travel gives me control over the first 90 degrees of throttle travel, which is where I spend most of my operation. That extra last few degrees of stick travel really opens the throttle (in this installation roughly an additional 50 degrees), to give me a good shot of steam when needed. (If you put the transmitter in Helicopter mode, you can really customize your throttle movement relative to the position of the stick, but you lose a bit of other functionality relative to controlling channels 5 and 6 which I use for lights.) 

But back to the throttle and its issues. I installed the "standard" sized servo and bench tested the installation. The first test was positive--the larger servo had sufficient oomph to move the throttle, even though it was "sticky." I also looked at the degree of "sticky" relative to pressure, and found it directly proportional to the pressure. Up to around 40 pounds, it wasn't that big of an issue. Getting up to 50 and 60 pounds, even the larger servo would struggle to move it, at least smoothly. Once the pressure dropped, the throttle got a bit easier to move again. 

So, after that test, I pulled the valve out of the throttle for a proper inspection. The threads on the throttle looked like they had been gripped a bit too tightly by a pair of pliers or something--flattish spots on opposite sides. Not having a proper die at my disposal to attempt to reshape them properly, I had at them with a small jeweler's file, fine sandpaper, and other bits and baubles. I was able to mitigate much of the damage to where you can't really tell by looking at it. On the microscopic level, I'm sure there's still something there, but I polished and smoothed it to the best of my abilities. 

After reassembling with copious amounts of steam oil, it was time for another test. This time the motion at higher pressures was noticeably smoother. It was still harder to turn at higher pressures, but the servo had no troubles with it. At this point, I'm satisfied to call things good, certainly good enough pending a proper shake-down run once the white stuff stops flying. I'm not 100% on the mount for the servo, as there's still a little more flexibility than I'd like to see which isn't necessarily what you want with chain-and-sprocket connections, but that's an easy mechanical issue. (On the other hand, I'd rather have a little flexibility than risk breaking the chain...) 

Later, 

K


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## steamlogger (Jan 2, 2008)

Some thing is missing. But I can't put my EYE on it.  

I ran my EBT #12 at a train show today. I stopped adding cars at 24, which is halfway around the track I had at the EBT in October, due to driver slip.


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