HSR-8498 lock up

[serithseraki]

In regards to my last post stating that I replaced the gears and wires on my robonova, I will say that it went seemingly well. I say that as it went smoothly and when finished the nova booted up and moved nicely to its standard pose. Although when I was re-creating its walking gait, I had it move slowly to see if any imperfections were present in the motion. During this I noticed that once it moved several degrees from the standard pose its movements weren't symmetrical. So I powered him down and moved his servos manually and noticed some resistance in the movement that wasn't present before powering him on. So I have now taken him apart and tested each servo individually. The electronics do not seem to be a factor but when moving the servo degree by degree with both the top case on and also off the servos seemed to bind up every other degree at random points. Furthermore, when the servo moved fully in one direction it would bind somewhat before moving in the other direction. Now I am perplexed by this because the gears are all new, the gear pegs do not appear warped, and I even bought a spare middle and top casing and still no difference. I hope the lubricant is correct as I used White lithium which I assume is correct. I am running out of possible fixes to attempt, so do any of you have possible ideas for me?

[ostro_goto]

I have two solutions!
1) Try a 15A UBEC, and lipo batteries! if not work, solution two !
2) buy another brand of servo

[serithseraki]

If I had the funds to afford such things I would, but sadly I can only afford minor fixes. I think it could be two things. One, the case needs replacing or two, the potentiometer needs cleaning. On most of the servos the problem ranges seem to mostly be between 54-56, 94-104, and 160-168 degrees. Has anyone else in the forum had servo lock up and found a fix for it? My current plan is to buy more lubricant and clean the gears to see if there is any grit present, then rearrange the gears and hope it works.

[ostro_goto]

When you have this problem, how many servo are connect to MR-C3024 ?
Try only one Servo at a time!

[serithseraki]

I have tested a single servo on the board and again with its symmetrical counterpart working in unison. The problem is not consistent between multiple servos, but random and leads me to believe the new gears may be imperfect.

[serithseraki]

Time for a slight update. After disassembling a servo and cleaning as much of the grease that was possible, I ran the servo and there was an improvement in its motion. This led me to believe the grease congealed and gummed up the servo. So after doing research I found that automotive stores have a more viscous spray version of the grease and my question to the forum is does anyone have experience with this type of grease? Furthermore, is there a specific cleaning solution that can dissolve the grease fully without damaging the gear?

[i-Bot]

If you replaced the gears due to a broken gear it is essential to remove all the existing grease in case it has broken teeth in it. I have replaced gears in the past and then had instant failure of new gears by failing to do this.

I don't know what is good solvent because the material of all the servo components is unknown. I use a lint free cotton cloth and a small paintbrush without solvent. Inspect with a magnifying glass for debris.

I then regrease with Futaba servo gear grease.

[serithseraki]

I had cleaned the case to the best of my efforts. I use a paper towel, antimicrobial cloth and a dental tree "the small pipe cleaner kind". I believe the white lithium grease I placed on the new gears was poor quality as it congealed and led to problems.

[serithseraki]

Would this be due to wear on the potentiometer from having it hold particular positions? I read elsewhere that the potentiometer could be cleaned, does someone know the means to do this and can explain it to me?

[PaulL]

Krud tends to build up in potentiometers over time / usage. If they're not fully sealed, you can clean them with electronics-safe sprays (they're referred to as "contact cleaner", "potentiometer clearn", and such). You basically saturate the pot using a small tube on your can of spray, getting the spray into the case of the potentiometer, and letting the spray run out. It's best to manually rotate the potentiometer while spraying. DO NOT do this with power applied. In the case of these Hitec servos, you'll need to get to the pot, meaning the board has to come out.

[serithseraki]

Is there a particular brand of "contact cleaner" that you recommend, or will any with a tube nozzle work fine? Also, do I have to let the unit dry for a set period after spraying?

[PaulL]

I can't say there's one I'd recommend, but I haven't had issues with any I've had around up over the years. I usually just go with whatever I can find at Radio Shack.

The sprays dissipate pretty quickly - shake out the excess, and wait 5 or 10 minutes (use a fan to dry it faster). On a surface, they dissipate VERY quickly.

I can't stress enough, you MUST use a spray intended for electronics repair. Don't use acetone or WD-40 or anything like those.

[serithseraki]

I ended up getting the CRC brand contact cleaner from a local hardware store. Although I still need to test it to make sure it doesn't dissolve plastic. But from my research I have seen people take the potentiometer apart and clean the contacts directly. Is there a way to disassemble the plastic case without destroying it or will spraying into the gap suffice? Furthermore, as a unrelated question, is white lithium the preferred grease for the brass gear on the servo motor? I ask as the motor seems to be tight and I read brushing oil on the motor shaft could fix this, but how would I do this?

[PaulL]

It's always good to test a spray on the plastic. Some soft plastics can be problematic. I can check the potentiometer in the burned out servo I have and see if there's an easy and non-destructive way to pull the shell off.

Regarding the lithium grease - I'd say NO to that stuff for ANYTHING in a servo! What I've seen is thick and very sticky, and not good for things that have to spin fast. I use some on my metal working machines, but only for slow moving purposes (manually rotated bits, etc).

I use the Hitec-branded servo grease in my servos (it's thin, but won't run away like oil). Be sure to use only as much grease as is needed - too much is as bad or worse than not enough. When you say the motor is tight, do you mean when you rotate the brass gear? You should feel the magnets when you turn the shaft, but the motor shouldn't be "tight" (but then, as I recall, there is no easy way to turn the shaft).

These motors are sealed, meaning they can't be easily lubricated properly. They're not even intended to be lubricated! But, as something to try, you would:

* Remove any grease on the gear end of the motor.
* Apply a drop to the bushing /axle area.
* Power it on without the adjacent gear and listen for the RPM to increase, meaning the oil is working in (no more than a matter of seconds should be necessary).
* Power down, clean excess, repeat a few times.

One thing to note about these motors - they have a fixed lifetime because they are sealed brushed motors. Once the brushes wear out, the motor is done. It would be nice if servos used motors with replaceable brushes, or better yet brushless motors, but it seems the majority use sealed brushed motors. In the case of Hitec, it's more frustrating because of how the motor is mounted to the casing - if you could find a replacement motor, getting the old one out is still a problem.

[serithseraki]

Thank you, that was far more information than expected, and this has helped me in considering the Dynamixel line for future projects. After testing the contact cleaner the CRC brand is good quality and it didn't damage my working potentiometer but made no difference on the possibly damaged one so I will rule that out as my problem. I believe the first gear is not meshing properly with the brass gear and I found some grease in the hole for where the axle sits "no idea how it got there" but after some thorough cleaning I may work. Regardless, it seems as though I am saving up for a mass servo purchase.