Help repairing servo

Hitec robotics including ROBONOVA humanoid, HSR-8498HB servos, MR C-3024 Controllers and RoboBasic
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Help repairing servo

Post by serithseraki » Sun Jan 22, 2012 9:41 pm

Post by serithseraki
Sun Jan 22, 2012 9:41 pm

My Robonova's servos were due for repair and I ordered replacement cable connectors and gears for all the servos. Now the problem at hand is installing the new parts. When I removed the bottom case from the first servo to expose the board and wire mounts I found some problems. First there seems to be glue on and around the board. Second to get to the wire mounts I must pull the board away from the case but gentle force did not make this possible. Now from my observation it looks as though the motor is mounted directly to the board and the motor is glued inside the servo case. So my question is how on earth do I take this apart without breaking anything?
My Robonova's servos were due for repair and I ordered replacement cable connectors and gears for all the servos. Now the problem at hand is installing the new parts. When I removed the bottom case from the first servo to expose the board and wire mounts I found some problems. First there seems to be glue on and around the board. Second to get to the wire mounts I must pull the board away from the case but gentle force did not make this possible. Now from my observation it looks as though the motor is mounted directly to the board and the motor is glued inside the servo case. So my question is how on earth do I take this apart without breaking anything?
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Post by PaulL » Wed Jan 25, 2012 4:25 am

Post by PaulL
Wed Jan 25, 2012 4:25 am

First off, it won't be easy - it would have been nice if Hitec just used screws for the motor, then you could slide it all out easily - but that's not what they did.

The motor needs to be unsoldered at all 3 points to remove the board (solder wick, solder sucker, etc). You can do the "heat, apply pressure, heat" approach, but it's easier to mess things up this way (torn traces, delamination, broken SMD connections, etc). I haven't seen glue holding the board in before, but who knows how sloppy they can get at the factory. I did notice the servo wires are glued from underneath (strain relief, I guess).

If you have ABSOLUTE CERTAINTY when flowing the solder at the servo wire connections on the top of the board that the wire has flowed through to the other side, you COULD pull each wire out one at a time breaking the glue and resoldering on top of the board, but such an approach is not without risk (torn traces, flicked solder from the wire to a component, etc).

I have a burned servo (2nd hand ebay RN-1), but haven't had any luck getting the motor out in a non-destructive manner.

I really don't like how Hitec did these servos - if you heat the motor connections, you're applying heat to the brushes through the motor connections, not a good thing. There is almost no "harmless" way to work on these things!!!

Good luck!

PS - See pictures, hope these help. I just heated and applied pressure bit by bit, the board here is obviously toasted anyway so nothing to lose. If I had to do a working board, I'd open up some fresh solder wick. Another option, you could cut the old servo wires (ensuring the ends contact NOTHING) and tack on new to the top of the board, just thinking out loud here.

Image
Image
First off, it won't be easy - it would have been nice if Hitec just used screws for the motor, then you could slide it all out easily - but that's not what they did.

The motor needs to be unsoldered at all 3 points to remove the board (solder wick, solder sucker, etc). You can do the "heat, apply pressure, heat" approach, but it's easier to mess things up this way (torn traces, delamination, broken SMD connections, etc). I haven't seen glue holding the board in before, but who knows how sloppy they can get at the factory. I did notice the servo wires are glued from underneath (strain relief, I guess).

If you have ABSOLUTE CERTAINTY when flowing the solder at the servo wire connections on the top of the board that the wire has flowed through to the other side, you COULD pull each wire out one at a time breaking the glue and resoldering on top of the board, but such an approach is not without risk (torn traces, flicked solder from the wire to a component, etc).

I have a burned servo (2nd hand ebay RN-1), but haven't had any luck getting the motor out in a non-destructive manner.

I really don't like how Hitec did these servos - if you heat the motor connections, you're applying heat to the brushes through the motor connections, not a good thing. There is almost no "harmless" way to work on these things!!!

Good luck!

PS - See pictures, hope these help. I just heated and applied pressure bit by bit, the board here is obviously toasted anyway so nothing to lose. If I had to do a working board, I'd open up some fresh solder wick. Another option, you could cut the old servo wires (ensuring the ends contact NOTHING) and tack on new to the top of the board, just thinking out loud here.

Image
Image
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Post by serithseraki » Wed Jan 25, 2012 5:06 am

Post by serithseraki
Wed Jan 25, 2012 5:06 am

Dang, I figured that would be the problem, well there goes my plans. Anyway, what if I did something like Omnizero's setup here?
[img][img]http://i44.tinypic.com/333ikv4.jpg[/img][/img]
Seeing as the breaks in my wires are not close to the case I could use the unbroken wires and connect a buddy board with mounted pins.
Dang, I figured that would be the problem, well there goes my plans. Anyway, what if I did something like Omnizero's setup here?
[img][img]http://i44.tinypic.com/333ikv4.jpg[/img][/img]
Seeing as the breaks in my wires are not close to the case I could use the unbroken wires and connect a buddy board with mounted pins.
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Post by PaulL » Wed Jan 25, 2012 5:22 am

Post by PaulL
Wed Jan 25, 2012 5:22 am

If the breaks are further away from the servos, I'd say yes, DO THAT, it's a better final result that gives you a better long term solution.

I've considered doing up some "termination" boards (nothing I have time for at the moment), mounting them on the cable sides of the arms and legs, allowing me to run thicker silicone-jacketed wire for servo power, and thinner wire for servo signals with fewer wires overall (common power running down the side of the leg with taps for each servo with separate wires for servos signals). There's a lot of insulation among all those power wires! Fewer wires would be better for a few reasons. :)

There was also an article here some time ago regarding a tube-like wire wrap mesh to protect the wires, but you'd only spend the time on that if you had to rewire everything (not possible with everything in place).

I'm curious, why are you replacing gears? Just worn, broken, or is this preventative? Make sure you use the right grease (I have the Hitec stuff that comes in the small metal tubes).
If the breaks are further away from the servos, I'd say yes, DO THAT, it's a better final result that gives you a better long term solution.

I've considered doing up some "termination" boards (nothing I have time for at the moment), mounting them on the cable sides of the arms and legs, allowing me to run thicker silicone-jacketed wire for servo power, and thinner wire for servo signals with fewer wires overall (common power running down the side of the leg with taps for each servo with separate wires for servos signals). There's a lot of insulation among all those power wires! Fewer wires would be better for a few reasons. :)

There was also an article here some time ago regarding a tube-like wire wrap mesh to protect the wires, but you'd only spend the time on that if you had to rewire everything (not possible with everything in place).

I'm curious, why are you replacing gears? Just worn, broken, or is this preventative? Make sure you use the right grease (I have the Hitec stuff that comes in the small metal tubes).
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Post by serithseraki » Wed Jan 25, 2012 5:44 am

Post by serithseraki
Wed Jan 25, 2012 5:44 am

Yeah I read the articles for the heat-shrink tubing and wire protectors, I just learned about it a tad too late :oops: . Also, as for the gears, the ankle, thigh, and shoulder servos after two and a half years have finally started to show their age. So seeing as the bot was already disassembled, I decided to save the effort of doing it later and replace them all.
Yeah I read the articles for the heat-shrink tubing and wire protectors, I just learned about it a tad too late :oops: . Also, as for the gears, the ankle, thigh, and shoulder servos after two and a half years have finally started to show their age. So seeing as the bot was already disassembled, I decided to save the effort of doing it later and replace them all.
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Post by serithseraki » Mon Mar 05, 2012 7:40 pm

Post by serithseraki
Mon Mar 05, 2012 7:40 pm

Time for an update, I got the replacement gears and wires in the mail and have installed the gears. Although I had encountered the problem of a few bearings coming apart "those were a pain to piece back together". Now I am on the difficult part, the wires. Thanks to RN1AsOf091407's pictures I got a better idea of what to do. What I plan on doing, seeing as I can't directly access the wires for desoldering or remove the rubber that surrounds them from the opening in the case is to use my dremel and drill a hole into the case above the wires. Then I will use a file to create an opening large enough for a servo connector sleeve to snuggly fit. Next I will cut away the case above the rubber till I can free the wires essentially creating a large rectangle hole above a smaller rectangle hole. Then I will cut the wires and attach male terminals with the housing and sleeve, push the housing into the servo casing, then glue the housing in place. After that I can take any length of servo wire attach a female connector and plug and play. Now the problem is the sleeve and connectors together create a great deal of length and would protrude from the servo which could be ugly and cause problems with motions. Furthermore, I worry when drilling that I may hit the colored wires and ruin a servo. Plus I would have to figure out a method to get the plastic dust out of the servo once I finish drilling. So my questions to the forum are is this even practical or am I insane for thinking this? Is it to risky, and is there a more compact alternative to using the servo connectors that can accomplish this?
Time for an update, I got the replacement gears and wires in the mail and have installed the gears. Although I had encountered the problem of a few bearings coming apart "those were a pain to piece back together". Now I am on the difficult part, the wires. Thanks to RN1AsOf091407's pictures I got a better idea of what to do. What I plan on doing, seeing as I can't directly access the wires for desoldering or remove the rubber that surrounds them from the opening in the case is to use my dremel and drill a hole into the case above the wires. Then I will use a file to create an opening large enough for a servo connector sleeve to snuggly fit. Next I will cut away the case above the rubber till I can free the wires essentially creating a large rectangle hole above a smaller rectangle hole. Then I will cut the wires and attach male terminals with the housing and sleeve, push the housing into the servo casing, then glue the housing in place. After that I can take any length of servo wire attach a female connector and plug and play. Now the problem is the sleeve and connectors together create a great deal of length and would protrude from the servo which could be ugly and cause problems with motions. Furthermore, I worry when drilling that I may hit the colored wires and ruin a servo. Plus I would have to figure out a method to get the plastic dust out of the servo once I finish drilling. So my questions to the forum are is this even practical or am I insane for thinking this? Is it to risky, and is there a more compact alternative to using the servo connectors that can accomplish this?
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Post by serithseraki » Mon Mar 19, 2012 7:02 pm

Post by serithseraki
Mon Mar 19, 2012 7:02 pm

Yet another update, I found a pair of Molex connectors that I believe are compatible with the servo wires and are flat enough to allow the brackets to move over them without hindering motion. The link is here.
http://shop.vetcosurplus.com/catalog/product_info.php?cPath=72_226&products_id=6847
Anyway, I plan on mounting these connectors to the side of the servo next to where the wires protrude, instead of my original idea, but my question to the forum is are these connectors usable? Furthermore, what would be the best method for mounting the connector housing to the servo casing? I was thinking of using a plastic epoxy but that may be too sloppy.
Yet another update, I found a pair of Molex connectors that I believe are compatible with the servo wires and are flat enough to allow the brackets to move over them without hindering motion. The link is here.
http://shop.vetcosurplus.com/catalog/product_info.php?cPath=72_226&products_id=6847
Anyway, I plan on mounting these connectors to the side of the servo next to where the wires protrude, instead of my original idea, but my question to the forum is are these connectors usable? Furthermore, what would be the best method for mounting the connector housing to the servo casing? I was thinking of using a plastic epoxy but that may be too sloppy.
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RN-! Servos

Post by engineer » Sun Mar 25, 2012 5:24 pm

Post by engineer
Sun Mar 25, 2012 5:24 pm

This may be to late but the motors are pressed firmly into the case. I just pushed down on the pinion shaft and got the motor and board out in one piece. RN-1's servo leads were to long so I soldered new connectors on. I got them from Hobby USA, they are made by Custom Electronics 834 East Houston Ave. Gilbert, AZ 85234 (480)558-1996 USA Part# CEL1171
They are called male even though they are hollow to go on the pins on the controller. The robonova method of stuffing the excess under the board leads to failure since so many points are under there.
The servo bottoms have breakaway tabs to allow the leads to exit fron the other side,filling the unused hole with silicone.
I replaced 10 of RN-!'s servos with HSR 5498SG's to give it more strength.
This may be to late but the motors are pressed firmly into the case. I just pushed down on the pinion shaft and got the motor and board out in one piece. RN-1's servo leads were to long so I soldered new connectors on. I got them from Hobby USA, they are made by Custom Electronics 834 East Houston Ave. Gilbert, AZ 85234 (480)558-1996 USA Part# CEL1171
They are called male even though they are hollow to go on the pins on the controller. The robonova method of stuffing the excess under the board leads to failure since so many points are under there.
The servo bottoms have breakaway tabs to allow the leads to exit fron the other side,filling the unused hole with silicone.
I replaced 10 of RN-!'s servos with HSR 5498SG's to give it more strength.
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Post by serithseraki » Sun Mar 25, 2012 6:31 pm

Post by serithseraki
Sun Mar 25, 2012 6:31 pm

How much force was needed to get the motor to budge? That was actually an idea I tried before but to no avail. Also, isn't it kinda bad to do that to the motor? Furthermore, did you remove the wires from the board or cut past the glued portion? Lastly, from my previous link, will the Molex connectors I got work? I should receive the connectors in the mail by Tuesday and was planning to merely surface mount the female connector to the servo casing and plug the wires in, but now I may rethink this.
How much force was needed to get the motor to budge? That was actually an idea I tried before but to no avail. Also, isn't it kinda bad to do that to the motor? Furthermore, did you remove the wires from the board or cut past the glued portion? Lastly, from my previous link, will the Molex connectors I got work? I should receive the connectors in the mail by Tuesday and was planning to merely surface mount the female connector to the servo casing and plug the wires in, but now I may rethink this.
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Post by serithseraki » Sun Apr 01, 2012 7:22 am

Post by serithseraki
Sun Apr 01, 2012 7:22 am

Time for another update. I got the connectors and although they will work for later plans I chose against using them now as soldering the wire to the servo's PCB would be cleaner looking. I have currently replaced all the wires for the arm servos and the new wire length is more manageable. Although when attempting to disassemble the hip servo I was unable to remove the motor and the connected PCB from the servo casing as the glue seal around the motor was too large and the piece wouldn't budge. I have tried using a low powered heat gun to re activate the glue to slide the motor out but to no avail, and currently I have only managed to make a slight indent in the motors exterior by pressing my screwdriver into it. I read in another forum that freezing the servo will constrict the metal enough to break the glue seal but I am skeptical. Will this damage the PCB and ruin the servo? Can someone give me any tips that could help?
Time for another update. I got the connectors and although they will work for later plans I chose against using them now as soldering the wire to the servo's PCB would be cleaner looking. I have currently replaced all the wires for the arm servos and the new wire length is more manageable. Although when attempting to disassemble the hip servo I was unable to remove the motor and the connected PCB from the servo casing as the glue seal around the motor was too large and the piece wouldn't budge. I have tried using a low powered heat gun to re activate the glue to slide the motor out but to no avail, and currently I have only managed to make a slight indent in the motors exterior by pressing my screwdriver into it. I read in another forum that freezing the servo will constrict the metal enough to break the glue seal but I am skeptical. Will this damage the PCB and ruin the servo? Can someone give me any tips that could help?
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