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Well, after the 5th successful run of my new Accucraft Mogul I decided to install the RC system. I already have a Spektrum DX6i that I have used for a couple of other models, so I decided to add the Mogul to my list. Using a Sub-Micro servo that fit almost perfectly in the rear cab window after a slight visit with my file and drill for mounting. The Mogul fired up nicely and as soon as I had raised enough steam, I switched on the receiver, moved the throttle forward on the radio and off she went. Well, I was okay for about the first 30 minutes and then the servo just stopped responding. First I thought that maybe the battery was dead, but after resetting everything and the servo still not responding, I knew that something was up. So I very sadly, ran the Mogul through the rest of the water and fuel. Once the engine was shut down, I removed the servo took it apart and sure enough the heat in the cab had proven too much for the nylon gears. The nylon gear that contacts the metal gear off of the motor had melted and the whole thing was useless. The servo was fried. A twenty dollar lesson in think before you install.

So now I am looking at the best options for my second try at this. Does anyone have any experience with these? What is my best servo to use that will not be effected by the heat in the cab? Is it better to use metal gear servos? Any advise is most appreciated.
 

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Isn't there a lesson learned here? Perhaps you should have considered the "Sparky" version of the Accucraft Mogul. I thought the whole reason for running live steam models were for their "hands on operation"? I've seen too many club R/C systems go awry from anything from batteries going dead to radio interference, and to not anticipate the effects of heat sufficient to boil water? A second try?
 

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Try the Hitec HS-81MG servos they have metal gears through out the system. Have used these in my Accucraft C-16 for over a year with no problems . Both servos are mounted in the cab, and one is fastened to the throttle tube/shaft of the engine itself. It is mounted on a standoff 3/4's of an inch from the throttle . It regularly gets to over 140 degrees with no ill efffects.

I have fitted 4 Accucraft locomotives with these and am sold on how they work.

Charles M SA#74
 

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Dwight is an expert on melting servos in the cab. /DesktopModules/NTForums/themes/mls/emoticons/crazy.gif /DesktopModules/NTForums/themes/mls/emoticons/w00t.gif I'm sure he will add details of his experience. I think in the end his solution was to insulate the servo from the heat of the boiler.
 

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I mounted the direction control servo on my Aster Mikes under the smoke box. I thought that heat might be a problem so I glued a small square of the ceramic matererial on the servo to insulate it from the smokebox. Unfortunately, it got soaked with oil and water and after about 2 years it became a heat transfer medium. This damaged the servo, but it did not melt the gears, it affected the electronics somehow and the servo at first just went nuts and was totally uncontrolable and then eventually stopped working altogether.

When I replaced the servo I installed the ceramic material again, but this time I wrapped it in aluminium foil in an attempt to keep the insulator dry. So far (about 6 years) I have not had a problem that I associate with heat damage.

I did have a problem with the so-called "metal" gears. The R/C system I have is one that toy cars (monster trucks) use. While I was preping one of my engines one day I made the mistake of turning on the receiver before I turned on the transmitter and the servo started swinging from one end to the other. My system has the ability for the transmitter to limit the distance the servo is driven when the transmitter control is moved all the way to one or the other end point. I had limited my system to about 1/2 half... i.e.: full movement of the "Steering wheel" (my Forward/Reverse control) moved the servo about 1/2 of its capable distance.

Unfortunately, the kid that was driving his new "Monster truck" down the street, steering it from one curb to the other did not have his transmitter limited like mine. This overdrove my servo to the point that the servo gears stripped. It all happened so fast that I was not able to shut off the receiver before the damage was done.

The infurating thing about this is that it was a "metal gear" servo... BUT, it contains ONE plastic gear in the gear-train! Obviously, THAT gear is the one that stripped. To replace the ONE plastic gear, I had to buy a gear "set", which because it is the "metal" type, cost almost as much as a new servo... and it contains that same plastic gear.

I assume the plastic gear is kind of like a fuse to save the motor if the servo gets stuck... it strips the teeth off and saves the motor from a high stall current. But I don't know why I had to purchase a bunch of metal gears in a whole set just to get the plastic one to repair the servo.

Metal gears might help in a high heat situation, but you might want to check to be sure that ALL the gears are metal or you may have a melted one anyway.
 

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If its hot enough to melt the plastic gears its way too hot for the electronics (most of which are plastic). You either have to insulate the servo or move it. Have you measured what the actual temperature is where the servo is located?
Regards,
Gerald
 

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Charles, The "plastic" gear is there to reduce/eliminate radio interference created by the metal to metal contact in the rest of the gear set. This metal to metal parts contact in why it is not good to use a low frequency (non 2.4 GH) radio in live steam applications.
 

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Posted By Charles M on 05/31/2008 11:34 PM
Try the Hitec HS-81MG servos they have metal gears through out the system. Have used these in my Accucraft C-16 for over a year with no problems . Both servos are mounted in the cab, and one is fastened to the throttle tube/shaft of the engine itself. It is mounted on a standoff 3/4's of an inch from the throttle . It regularly gets to over 140 degrees with no ill efffects.
I have fitted 4 Accucraft locomotives with these and am sold on how they work.
Charles M SA#74




I second this recomendation. I use the Hitec servos with metal gears. When I go to buy a new one I always tell the shop owner what I am using it for, and it has to withstand heat and stress. Have never had one melt or malfunction in any way.
 

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Sounds to me like you have the servo mounted too close to the boiler. Try moving is to a different location away from the heat.

I think in the end his solution was to insulate the servo from the heat of the boiler.

Actually, that was never the problem (though I thought it might be). It turned out the pushrod connecting the servo to the J-bar was too thick with not enough flex. This put a lateral load on the servo, causing it to constantly buzz, and eventually overheat and burn out.

I thought the whole reason for running live steam models were for their "hands on operation"?

I don't think everyone should be required to enjoy the hobby exactly the same way you do. If you only run on level track or mild grades with good access, manual control works fine. If, however, you run on people's ground-level layouts that have stiff grades and limited access, R/C becomes almost a must. There's still plenty of "hands on" in prepping the loco for its run. Whatever floats your boat. :)
 

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Discussion Starter #10
Thanks everyone for the tips. I think that the two problems that I had with the installation was first the size of the sub-micro servo. [The smaller it is the less heat it will take) and the amount of torque necessary to rotate the throttle. It was just too much for the servo. I think that I have decided to get a servo with all metal gears (if I can find one) and use the chain drive method. I like the look of the setup as well as the ease of installation. My only problem now is to figure out the best way to install the control to the johnson bar. Accucraft really didnt leave us much room to work with when they placed the lubricator where they did. Does anyone have any suggestions that would not involve drilling the Johnson Bar? I dont have a drill press, so there is no way for me to do this safely. Any suggestions are appreciated.
 

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I started out with a 16-tooth on the throttle and a 30-tooth on the servo, but it didn't work well since I did not know I could correct the situation in my DX6 programming. I did not have enough travel.

Since the gears are inexpensive, I bought additional 32, 36 and 40-tooth gears for the servo and a 12-tooth gear for the throttle. I experimented and found that the best combination for my K-27 is 36/16. This combination gives me enough torque to close the throttle completely and initially open it. Travel after that is easy for the servo.

Once I did this, I found that I only got 180° throttle travel on the servo movement. So I learned that I could program my DX6 to give me 150% movement on the servo and now I get 270° on the throttle.

One word of caution: The large gears fit perfectly on the Hitec servos, but the small gears do not fit on the throttle shaft. So you will have to make a bushing out of brass tubing into which you can drill a hole and use a set screw through the gear hub and brass tube to set against the throttle shaft.

So the moral of my story is to purchase several inexpensive gears and experiment. Also buy a couple of feet of chain and have one for each combination of gears, plus some spare length.

Since fabricating my system, I've seen people with fewer teeth on the throttle allowing for a smaller gear on the servo. Perhaps someone can chime in with their solution.
 

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I don't know the Acc Mogul, but maybe you could "think outside the box"... or in this case... "outside the cab". Is there room somewhere else to mount the servo? You don't really have to connect to the Reverser Lever in the cab, you could attach to some other place along the chain of connections between the Reverser Lever and its ultimate destination. On my Aster Mikes, I put the servo under the smokebox and ran a reach rod back to the bell crank to the lifting link. I completely disconnected the Reverser Lever in the cab.
 

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I have radio controlled my Aster Pannier. I had trouble failing servos. The servo sits right up next to the back of the boiler.

I went with a Hitec HS-85MG from Servo City. I attempted to insulate the servo from the heat by using a foil strip and some leftover Aster ceramic sheet.

So far it has been working well.
 
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