Model Boat Mayhem

Technical, Techniques, Hints, and Tips => Other Technical Questions... => Topic started by: lakeside on April 23, 2009, 01:28:05 am

Title: Servo reduced performance
Post by: lakeside on April 23, 2009, 01:28:05 am

My Hitec HS-765HB servo is showing reduced output. It's rated torgue is 98.07 Nmm (11 kgf cm) at 4.4 volts. but actual torgue is down about 50%. There is no slop in the gearing and I suspect the motor is on the way out. Is there any way to service these servo motors to restore rated performance.

Would apporeciate any member, having had similar experiences, sharing their solutions. TIA

Title: Re: Servo reduced performance
Post by: Subculture on April 23, 2009, 10:26:07 am

The motors used in hobby servos are cheap units not designed for servicing. It may not be the motor anyway, could be the drive transistors going bad.

Whichever it is, it's simpler, cheaper and easier to just order a new one.

Title: Re: Servo reduced performance
Post by: lakeside on April 23, 2009, 11:38:01 am

Thanks for the response Subc.
Do you know if an electical circuit is available to check out the transistors?
Ragards

Title: Re: Servo reduced performance
Post by: andrewh on April 23, 2009, 12:20:36 pm

Lakeside
While I am modest in my elecrtrical understanding, I do know William of Ockham well.

He requires that the simplest solution that fits the facts is the most likely, and this is the motor getting weary.  If you want to take the servo apart and try and scoosh contact cleaner into the motor case.  sadly servo motors are always sealed cases so you need to use the fixing screw holes on the front face (assuming it has any)
You could replace the motor - this is perfectly straight forward as long as the new motor has the right gear fitted, but I don't think they are available as spares.
The output transistors (on my dead one) are (or appear to be) FETs, but I would not expect any transistor to "partly" work.
 I know this is possible but normally if the smoke is still inside they work perfectly.
andrew

Title: Re: Servo reduced performance
Post by: lakeside on May 07, 2009, 12:45:42 pm

Thanks for the reply Andrewh. Searched for a new motor but, as you surmised, they are not available as a replacement part. Decided to buy a new servo, HS815BB, with a greater torgue and avoid the hastle of reconditioning the failing HS765.
Regards

Title: Re: Servo reduced performance
Post by: malcolmfrary on May 07, 2009, 09:35:35 pm

In the past I have recovered the bearing from a dead BB servo and transplanted it into a non-BB one (same make).  It was a drop in replacement for the plain bearing fitted.  Just a thought, must be worth a look.