A Servo Issue - perhaps?

Rcsailing.net Technology Discussions
1

As I have said before, my electronics knowledge is short, and very limited. I read, take the average suggestions and buy accordingly. Normally this works well for me, but to disect problems with the radio stuff is something I seldom try - or need to do.

This weekend, I had a Hi-Tech 815BB sail arm servo (1/4 scale) attack me with some some strange and never before observed behaviour. Just wondering if any one can provide a suggestion of something I might have missed - short of replacement time…

As noted - it is the big HiTech servo with single arm sail control. I also am using a small rudder servo - both mounted to a narrow, in line radio board. Upon firing up the Tx with Rx plugged in, the rudder stick worked fine, left and right worked. The sail servo would work to pull in the sails, but reversing the stick direction failed to generate any movement in the sail arm. Turn off the Tx and physically move arm back to full-out sheet position, move stick to mid-point, turn on Tx and servo arm moves to half-in position and stops. Would not return, but would move to complete in-haul.

So - I pulled entire radio board, and proceeded to test. Reversing plugs at the receiver confirmed both Tx and Rx worked, as now the reversed sticks controlled the opposite receiver function. (i.e. - former rudder stick now controlled one direction only winch arm, while the former winch stick now controlled the rudder servo in both left/right direction).

After several different checks to verify the “Y” Harness and all plugs were clean, I have narrowed it down to the fact that the 815BB servo has now only one direction, and will not respond to opposite control stick movement.

Here comes the question - “Is it worth sending the servo in for exam and repair, or for the $60 (US) am I just better off to place in a dumpster and add a new servo to my order from the hobby shop?” I am just guessing the guys will have a minimum “bench charge” of $45 - so any costs to repair bring me closer to the cost of a new servo. Perhaps it is only a bad pot - or whatever … but then again, I may be overlooking something with my limited radio knowledge. Building boats I can do - troubleshooting beyond electronic basics (switching plugs and verifying batteries are installed correctly is about my limit).

Any help or suggestions appreciated. I have about two weeks before my next sailing date - but I do have a back-up 815 I will probably install. I just don’t know if it makes sense to fool with the bad one.

Thanks

2

I would go the route of installing the backup 815. Then play with the old one to see if it can be restored to life. If ‘yes’ then you have a new backup.

As to the problem, you have isolated it to the servo by swapping the plugs with the steering servo. So what could it be? Has it got wet? If ‘yes’ spray with electric-safe water repelling spray.

Is the problem electrical or mechanical? When you tell it to go ‘out’ can you hear any motor noise?

If ‘yes’ then it could be a stripped gear or gear loose on shaft or loose potentiometer drive.

If ‘no’ then electric problem.

As it pulls ‘in’, I would suspect a problem on the circuit board. Probably not worth spending the money to troubleshoot/fix.

3

Hi Dick, sounds like you knocked out one of the power transistors, I would send it back to Hitec, they have a vary good 2 year warranty
john

4

Quote: I would go the route of installing the backup 815. Then play with the old one to see if it can be restored to life. If ‘yes’ then you have a new backup.

As to the problem, you have isolated it to the servo by swapping the plugs with the steering servo. So what could it be? Has it got wet? [nope - very dry boat] If ‘yes’ spray with electric-safe water repelling spray.

Is the problem electrical or mechanical? When you tell it to go ‘out’ can you hear any motor noise? [silence - only hear servo when doing the in-haul]

If ‘yes’ then it could be a stripped gear or gear loose on shaft or loose potentiometer drive.

If ‘no’ then electric problem.

As it pulls ‘in’, I would suspect a problem on the circuit board. Probably not worth spending the money to troubleshoot/fix End of Quote

Quote: Hi Dick, sounds like you knocked out one of the power transistors, I would send it back to Hitec, they have a vary good 2 year warranty [Unfortunately it is out of warranty - I did email HiTec and ask for estimates to look at, but also found the cost of a new one has dropped from the $60 originally spent. It is now down to $45 which will pretty much equal bench time to troubleshoot. A friend who is into ham radio as technician has volunteered to take a look later this fall.] End of Quote

The back-up servo is in and functions - which confirms any issues are not with Tx or Rx.

Thanks for the suggestions, guys.

5

For what its worth, I bought a Hitec HS-5955TG on eBay and it lasted a day. A sheet got stuck and before I realized what was happening it ceased to work. I suppose it was my mistake yet I mailed it to them with a note… I don’t know if it was under warranty or not. Thought I’d get a “we regret” letter but instead they sent a new servo. A nice gesture and a solid customer relations move. Thanks HITEC.

yar

6

Hi - haven’t seen/heard from you lately. What have you been working on?

Thanks for the HiTec suggestion. Even Servo City confirmed that HiTec does this “exchange” sometimes. Will give it a try.

7

I appreciate your greeting, Dick. Yes, away for the summer on work… my sailing plans shot. Refitted MacDaddy ketch with canting keel and adjustable backstays, now w/4ch radio (all possible with advice gleened from you all) for recreation on Black River, PH-Mac Boat Week (Michigan) in mid July but family issue shelved that fun. Oh well, there’s always next year.

I’ll need to catch up on my reading to see your projects. Big boats, si? Glad to be back, seeing familiar avatars.

yar

8

Well Dick, being an electrical engineer that this servo is not matching your boat. For small sized boat, medium size servo is adequate but you have to check also whether any unwanted noise is generating from it?Best option available though is to check your Servo with the company.Try to alter the plugs connected. Hope this helps you little bit at least.

9

Hi Dan -
yes, I have exchanged servo plugs and problem remains the same.

I did get a response back from HiTec and am looking for a proper size box to send it in. They suggest a maximum of $30 to fix/repair, so I will be giving it a try since a new servo is about $45 - $50.

In the meantime, I do have my back-up 815BB so can continue to sail. I will be interested in hearing what the problem was. Will post when I find out.

10

To close out the thread …

Servo sent to Hitec
Great (and fast response) advising a transistor had “expired”
Since servo was more than 2 years old (like maybe 8-9 ?) they weren’t going to repair.
Replaced old servo for new one at “Repair Cost” of just under $30 (US)
Cost is well under new servo retail by at least 1/3
Replacement servo on it’s way back as I write.

Great experience! Highly recommended company for product support and response.

:zbeer: