Servo City Gear Box problems

[David Santistevan]

As some of you may have seen, I installed a Servo City SPG7950A038A90 gearbox in my new gas tunnel. During the final setup a couple of weeks ago we discovered that the gearbox no longer worked. On inspection it appeared that the servo had burned up. I sent it back to Servo City and they confirmed the unit had burned up. I discussed with the the various possibilites as to why it burned up and they seem to think it was too much load for too long. I could not fathom that since the unit puts out 1500 inc/oz of torque and it had never been mounted in the boat. We had only hooked it for a short time to test the rotational speed with no load and only for a few minutes.

The replaced the servo and sent it back to me last week and I put it back in the boat. I went through the setup and everything appeared to work normally with no problems. However When I got it to the lake the servo was burned out again.

Here is what I think is happening and I wanted to see if anyone else is having this problem. A generator and a motor are basically from a mechanical standpoint the same thing. I think what is happening is that when the engine under it's own weight swings to the side it therfore manually turns the gearbox. At the gear ratio used to generate the 1500 in/oz I think it is spinning the servo fasted enough to generate an electric charge to burn out the servo.

Thie may seem crazy but here is some real world experience to back it up. I work in the computer industry. I have seen it over and over again where computer mother boards have been burned out when some take ther machines to blow the dust out using compressed air. They spin the fan motors in the computer with the compressed air fast enough to generate an electric charge great enough to burn out components.

Has anyone seen anything like this ?
D

 

[David Santistevan]

It is a digital servo and I am using Futaba FAAST, nope I am sure I was in PPM mode.

D

 

[Brandon Atwell]

We've used the gearboxes ever since we first put our original gas tunnel together. So 8 years? The only time we've lost one was when we flipped the hull. What gear ratio are you running? And what size battery?

 

[RonShaw]

David,

The gearbox is waaaaaay overkill for that boat. Rip that extra weight out and use two 805MG's with #6 rods and the Dubro Monster #6 ball links with 7.2v 4600mah nmhi pack. Dick Loeb helped design that boat to "set" in the turns without requiring you to "muscle" it through the turns. Thats what I ran in mine for two years and it would drive the pins and it won just about every heat it finished. Good luck.

 

[VenomCC]

I installed the robotic servo from Servocity when I built my tunnel and have had zero issues with it.

 

[David Santistevan]

I used a 2C LiFe battery rated @ 6.6V but it was actually putting out around 8V. I checked with Servo City and they said that was fine after the first one. I am not sure what the gear ratio is. This is a very odd scenario, We are refitting now to use two Savox servos @ 450 in/oz inline. Greg the servo was plugged into the receiver but it doesn't make a lot of sense to me either.

 

[moparbarn]

david, i wouldn't think that the ob swinging on the servo would turn fast enough or far enough to generate enough power to hurt anything. have to believe that a lot more rpm & full revolutions would be needed. really don't know enough about the circuitry used in the servo & rx, but have to think that there are diodes in there somewhere to prevent it from happening? like i say, don't know just thinking out loud.......

 

[James E Beasley]

You need to provide the power to the servo direct, not through the RX. Use a Hitec heavy duty Y harness to do this and do not use a standard RC on off switch. Either go buy a switch rated above the expected amp draw of the servo at stall (about 5 amps) or use deans ultra plugs outside the radio box as your switch. The total weight of the servo city setup is no more than two 1/4 scale servos, and provides the benefit of a very strong bearing supported load bearing bell crank to protect the servos. Check for binding at all points, hinge pin, push rods against exit holes in the radio box, etc. These servos are monsters and will easily hide a misaligned setup on the bench. I persoanly use Sanyo Sub-C High discharge rated NI-Cads 5 cell pack with heavy duty leads made by NOBS Batteries. I would be wary of using the 3S lipos without a regulator and that adds weight and complexity. If all of that fails I suspect a defect in the external pot wiring. Does not happen often but can have a short with soldering and all, humans asembled it for you right. Like others have said, we have been running these for years with much success. I have won two Gas Tunnel Championships with my setup. Hope you find your gremlin. James

 

[James E Beasley]

Also, I assume you know how to set the system up but in case not, during installation of the robot unit, do not tighten the sinch collar on the steel shaft. Power the setup on and use a screwdriver to turn the center shaft R & L to find the Potentiometer's center. Then adjust your end points for only about 15 degrees of rotation each way, that is all you need. Once the servo is centered and the throws are equal, you can tighten the sinch collar and install the servo arm. You may have to make center point adjustments using your radio to center up the arm. Oml now is it safe to install pushrods. If you don;t do all of this prior and hook everything up prior you can swing to a lockup situation which will overload your servo and break stuff! James

 

[Tony Jacuzzi]

Is it a digital servo and what radio system are you using.

If its a futaba radio and you have hrs mode on ( high speed) you can burn up a servo in seconds

Hitec analog servos last about a minute on hrs mode before the smoke comes out. Futaba servos last a bit longer but they dont like it either.

Can someone explain HRS mode. I thought that was specifically for Digital servos and PPM was to use digital and non digital mixed?

 

[David Santistevan]

Jim,

thanks for the info, some good stuff there. I will be talking with Servo City techs this morning to see what they have to say.

D

 

[RonShaw]

David,

Looking forward to getting your feedback on the lower unit!!

 

[David Santistevan]

I talked with Kyle at Servo City and he has confirmed this can and has happened. He says it is pretty rare but apparently something in my setup makes it much more likely. He confirmed a diode between the servo motor and the board should solve the problem.

Ron, I am will certainly post my experience with the geared lower. I have had it in the water for a couple of runs but nothing real high speed yet.
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[moparbarn]

david, i'm surprised that a diode isn't included inside the servo already. the problem may be related to the gear box & the increase in both revolutions & speed at the servo when the engine turns the servo. electrons flowing upstream apparently are a bad thing .

 

[Matt Minassian]

I doubt our situations are the same but I had an instance at our last race where I actually left the servo's turned on with my Megaservo in my tunnel but had the transmitter turned off. I didn't realize it until it was too late and it actually smoked every last piece of my electronics. Doesn't sound like you left your battery on though.

Matt

 

[RonShaw]

I talked with Kyle at Servo City and he has confirmed this can and has happened. He says it is pretty rare but apparently something in my setup makes it much more likely. He confirmed a diode between the servo motor and the board should solve the problem.

Ron, I am will certainly post my experience with the geared lower. I have had it in the water for a couple of runs but nothing real high speed yet.

D

David,

Are you using the clutch or removing like I will do? Was the clutch bell hard to remove? Thanks.

 

[David Santistevan]

I did not use the clutch. Mine was not installed when I got the unit so I really don't know how hard it is to remove. I suspect it isn't too hard. Be sure to break to lower case open and fill with 90W, mine had very little in it from the factory.

D

 

[RonShaw]

Great. Thanks for the tip David. I will check to make sure mine has plenty of oil. I am looking forward to seeing how this beauty performs.