Servo Gearbox servo replacement

[LawlessMan]

This question is for anyone running a ServoCity gearbox in a gas outboard tunnel. Although the latest gearboxes have programmable digital servos that will operate on 7.2v
Li-Po packs, the original servo gearboxes used analog servos that operated on 6 volts. Many people had no trouble with them. but over time, some of the analog servos developed dead spots from holding the servo in one place for relatively long periods of time, like the length of time it took to go down the straightaway from buoy 3 to 4. I also know some people have replaced their analog servos with digital servos, like SAVOX and other brands. This change basically eliminated the internally mounted potentiometer which had been taken out of the servo case and replaced with an external one mounted on the bottom of the output shaft and hard-wired back to the servo. My question is: What effect, if any, did this have on the steering of the boat? Did it cause over-steering or any other problem associated with the "loss" of the direct feedback of the external pot? Are transmitter "end point" settings being used to adjust the servo travel, or, prehaps, are external programming methods being used to reduce the travel? I am sure that there are still several of the older style gearboxes in use that may develop, or may have already developed the dead spot problem, causing erratic steering. Anyone care to offer some feedback on this issue?
Thank you,
Fred, the Lawless guy.

 

[chriscarbon]

I was helping a friend that had a similar set up. To start with everything worked ok, however a lot of steering had to be taking out. After time and several dunks, he had dead spot problems. I though the external potentiometer needed changing. This has been sometime ago. If I were having the external potentiometer changed I would make sure it was the 60 degree one hoping it would last longer and have less problems. I am thinking the newest gearbox setups are digital. Someone running a gas tunnel that the steering is working well now should be able to help.

Chris

 

[Wasted wages]

I'm surprised at this point, someone hasn't built or invented a hydraulic type of steering for the outboard's. With all of the miniaturization of robotics etc, there might be food for thought on this.
Especially on the gas boats with larger boats and more room to work with. Maybe something as simple as a servo moving a push - pull cylinder.... 1/8" nylon tubing routed to the back of the boat driving a slave cylinder side to side...filled with some thin oil..

seems doable ? thoughts ??

 

[Daniel's Racing]

Many now can just go to a servo with plenty of guts. Plenty of servo's out there now that will directly steer a gas outboard.

Setup the linkages mechanically correct so servo is using full travel these provide plenty for gas outboard.

SW2290SG-BE - Waterproof Monster Torque High Voltage, Brushless, Digit – Savox USA

 

[Shannon Muth]

The SW 2290SG-BE is an awesome rudder servo in my 35% Yak 54, but in my opinion not enough for a gas outboard. 2 ganged together would be perfect. It will require a radio that will allow you to slave a 3rd channel to the steering channel. I prefer the pictured Servo City assembly. Pay attention to gear lash and linkage geometry so that slop or binding is minimized.

 

[chriscarbon]

Shannon, Is gearbox that you have the equivalent of the SG20 series. Also, what is the diameter of the large gear and does yours have a potentiometer or is it digital.
Thank You
Chris

 

[LawlessMan]

To address Daniel's and Shannon's comments , the difficulty I have seen with really huge, or doubled servos is the speed at which they rotate. A big sail servo might be a candidate, but they are super slow, proper for a sailboat, and do they have the torque to pass muster? On the other hand, you cannot have the boat whipping around turns because it will easily go into a 360 spin, or flip, Sure, you can slow down the servo speed with the transmitter, but it seems to me that solution will only work if you check the speed setting every time you run. The 5:1 gearbox reliably reduces the turning speed to 1/5th of the servo's natural speed, which I have found to be much more convenient than a transmitter setting. Frank's suggestion about using hydraulics sounds interesting, but to my (machinist's) mind that would over-complicate the setup. You would need more moving parts to make it work. The gearbox with the new digital servo is solid and reliable. The original analog servos were just not up to the challenge presented by the gas boat, but we didn't know that until they were tried and tested. Now that the gearboxes come with reliable digital servos and the actual price has dropped considerably I think you would be hard pressed to find a better setup. Can you find two servos to slave together that will put out 1750-2000 oz/in of torque and turn slow enough, for under $125? Please let me know if you can.

 

[Shannon Muth]

I don't believe the the large gear changes from one ratio to the another, just the pinion gear. Choose the ratio that will get you to 1500 oz/in minimum. I completely agree with Fred's comments, I usually will reduce the servo speed on all of my tunnels. It would be nice if Savox made a continuous rotation servo with the specs of the SW 2290SG. I don't believe the 2290SG can be modified for continuous rotation as the potentiometer is mounted to the PC board. A Hitec 7950 TG with the gearbox pictured is 1500 oz/in plus.

 

[Daniel's Racing]

To address Daniel's and Shannon's comments , the difficulty I have seen with really huge, or doubled servos is the speed at which they rotate. A big sail servo might be a candidate, but they are super slow, proper for a sailboat, and do they have the torque to pass muster? On the other hand, you cannot have the boat whipping around turns because it will easily go into a 360 spin, or flip, Sure, you can slow down the servo speed with the transmitter, but it seems to me that solution will only work if you check the speed setting every time you run. The 5:1 gearbox reliably reduces the turning speed to 1/5th of the servo's natural speed, which I have found to be much more convenient than a transmitter setting. Frank's suggestion about using hydraulics sounds interesting, but to my (machinist's) mind that would over-complicate the setup. You would need more moving parts to make it work. The gearbox with the new digital servo is solid and reliable. The original analog servos were just not up to the challenge presented by the gas boat, but we didn't know that until they were tried and tested. Now that the gearboxes come with reliable digital servos and the actual price has dropped considerably I think you would be hard pressed to find a better setup. Can you find two servos to slave together that will put out 1750-2000 oz/in of torque and turn slow enough, for under $125? Please let me know if you can.

The radio set on 1% servo turn and return speed it is really slow. Literally several seconds to rotate from center to the locks. Set it up with about a 50% Ratio with servo horn half the width of the engines mount points and it will be plenty slow. Set the speed low and the exponential so it is slower around neutral and plays catch up the further you turn. Easy to electronically fix the speed issue. All water proof and precise movements with up to the full servos torque centering power. Turn the wheel slow the servo will move slow. Turned down it would not be touchy at all.

Remember this video is turning wheel instantly to the locks quickly.

 

[LawlessMan]

The radio set on 1% servo turn and return speed it is really slow. Literally several seconds to rotate from center to the locks. Set it up with about a 50% Ratio with servo horn half the width of the engines mount points and it will be plenty slow. Set the speed low and the exponential so it is slower around neutral and plays catch up the further you turn. Easy to electronically fix the speed issue. All water proof and precise movements with up to the full servos torque centering power. Turn the wheel slow the servo will move slow. Turned down it would not be touchy at all.

Remember this video is turning wheel instantly to the locks quickly.

I can appreciate the amount of testing and experimenting that went into that setup. I'm a lazy ass when it comes to setting things up, so I don't want to fiddle and adjust. The ServoCity gearbox SG12-50-CR that I sell (slightly modified to work with my steering rod set) cranks out 1750 oz-in at 6 volts, about 2000 at 7.2v. It rotates at 12 RPM, so, at 5:1 reduction, that is 2.4 full rotations of the output shaft per minute.. That would take about 1.4 seconds to go from -10 degrees to +10 degrees (assuming 1-1 ratio between the servo arm and drive), or .7 second to go from center to as far as you would probably want to turn. For my boat, a Woodstuff with my gas drive, that was plenty fast enough for good turning, but not enough to get into trouble. If that is too fast, then I would adjust other parameters.
Fred

 

[Mike Mullarkey]

I don't believe the the large gear changes from one ratio to the another, just the pinion gear. Choose the ratio that will get you to 1500 oz/in minimum. I completely agree with Fred's comments, I usually will reduce the servo speed on all of my tunnels. It would be nice if Savox made a continuous rotation servo with the specs of the SW 2290SG. I don't believe the 2290SG can be modified for continuous rotation as the potentiometer is mounted to the PC board. A Hitec 7950 TG with the gearbox pictured is 1500 oz/in plus.

I have 2 of the Savox 2290 servos in parallel and will let you all know how it works. Yes it was costly but think it can be slowed down enough to do as good of a job as the gear solution.

 

[LawlessMan]

Any solution that works consistently and well is a great solution. The gearbox was AN idea, but not the ONLY idea.