Failed Servo's

[PaulP]

I had two servo's fail on my KHR-1HV within 2 weeks of it arriving. I know of at least 1 other person who has mentioned having a similar failure in a short period of time..

With a lot of assistance from the guys at LynxMotion, I have identified the failure and managed to get the failed servo's working again.

After the event, I have also found this link....

http://babelfish.yahoo.com/translate_url?doit=done&tt=url&intl=1&fr=bf-home&trurl=http%3A%2F%2Fwww.t3.rim.or.jp%2F%7Etom-i%2Frobo%2Ffetrep.html&lp=ja_en&btnTrUrl=Translate

It appears this is a known fault, if not by Kondo then at least by the guy who wrote the article....

It appears that they use a FET in the Servo, HAT3004 which is prone to fail. There are a lot of R.C. cars that use the chip and there are lots of articles about how to repair / upgrade them.

If you have such a failure then, If the servo is still free to turn manually when unpowered, it is likely that you have suffered this failure and this fix should work. I have carried out the procedure and so far it seems okay.

If a servo fails but becomes tight to move when unpowered, it is more likely that, although the FET's will have blown, the cause is due to over-stressing or damage to the gears / motor. Even if the servo is still in the robot, it will feel more resistive to movement than the others.

I would like to stress that this post is not meant to point the finger at either Kondo, who may be unaware of this issue, or the People on this forum who have been very supportive in this problem. I'm hoping that this is an unusual circumstance but just in case someone else is as unfortunate, this post may point them in a cheaper direction than having to import replacements from Japan.

[tempusmaster]

Hi Paul,

Good hunting, and good post. The blog entry you found is on Ishii-san's (Green Eyes and T-Storm) old blog (KHR-1). He's also on one of the top soccer teams for the KondoCup competitions, and was featured on the recent NHK television segment here on Monday:



So he definitely knows what he's talking about.

I looked up the FET issue in the KHR-Perfect Book this evening. It turns out that there's a short write-up on page 52 that explains that if the servo gets stalled for too long then one of the FETs might fail, along with a caution to avoid anything that would block the servo movement or stall it. The KRS-784/786/788HV are specifically mentioned in the text.

[PaulP]

I think its the nature of the beast, we are asking a device originally designed for other purposes to perform near-to and sometimes beyond its performance capabilities..

Personally I would have prefered some form of comment from Kondo with the kit saying, 'We know this can happen and if it does then heres how to fix it' but thats not good company policy for anyone.

I don't think there are many people in this hobby who would be put off by being told what to watch out for. Most people are dubious when there isn't any information. But isn't that what the forums are all about?

Still I'm in this to learn and gain experience and thats what I achieved. I'd never taken a soldering iron to SMT type hardware before so that was a first.

[daxx2k]

So any news about this problem? I got my servo failed in the same way....