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Old Jan 30, 2013, 10:55 PM
Detail Freak
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Harbor City, CA
Joined Oct 2003
21,862 Posts
I'll be happy to buy some of the DS11 from you if you want to wait until I work some OT in the next few months(weeks I hope).
NO bodybuilder servos though! (you know the ones that you made lift weights, 10 reps of 60oz...)
Let me now what you want for them.

R,
Target
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Old Jul 29, 2013, 07:38 PM
RIP MC
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United States, CA, Midway City
Joined Dec 2003
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I finally was able to get to test a batch of these servos and I have to admit that they are pretty decent.

Of course I had a hunch when I got to briefly test Joe's 181's which are the Japan version of these 398s.

I did not test the HV series.
The resolution and deadband numbers are:

Operating pulse width = 780us - 2180us = 1480us center.

Deadband = 1 microsecond = 1400 possible steps.

1 degree = 10us = each trim step of 1us gives .1 degree resolution.

The theoretical max travel for the servo is 140 degrees, but this will depend on your tx/rx combo. Some tx/rx operate at pw between 880-2160 with most of them falling in between 900-2100.
Even with the lower numbers one should be able to get a total travel of 120 degrees with this servo.

For the current numbers:
At idle, the servo is pulling .01A.
Buzzing we are at .11-.19A
Quick back and forth = .56A ( the dive then into zoom part of a TD/F3J launch)
Springing of the TX stick (stalling) 1.18A

Unloaded speed is very consistent at .11sec for 60 degrees of throw (again at 6.6v).
I have not tested the torque rating yet.

The accuracy is very good with this servo. I tested 2 of them and both are consistent. I do noticed that there is a very slight over shoot of the servo to a commanded position, but will settle right on that position a split second in.
This is actually not such a bad thing as it helps keep the electronics, especially the motor a bit cooler by keeping the arcing of the brushes lower vs trying to stop "on a dime" and allowing the servo to get to a commanded position faster.

The only thing to watch out for is using the 398 non hv's on 6.6v LiFe's. However, from my personal experiences with JR's 6v rating, this shouldn't be an issue... YMMV though.

Conclusion: My Next F3J ship will have these in the flaps.
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Old Jul 30, 2013, 06:41 AM
Malta & Newport
United States, RI, Newport
Joined May 2010
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I ve had the 398 hv for a year in 2 Supras and really cannot fault them for accuracy. But I also have them for ailerons which is possibly overkill, what do you have in mind using in your tips? Al.
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Old Jul 30, 2013, 06:29 PM
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United States, CA, Midway City
Joined Dec 2003
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Quote:
Originally Posted by alexhallmalta View Post
I ve had the 398 hv for a year in 2 Supras and really cannot fault them for accuracy. But I also have them for ailerons which is possibly overkill, what do you have in mind using in your tips? Al.
I'll probably go with either the Atx 809 or another set of 398's.
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Old Aug 01, 2013, 10:48 PM
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United States, TX, Houston
Joined Aug 2006
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I have 398HV all around on a Perfection and MKS all around on another. Because I run Hyperion LIFE the MKS are on individual regulators.
No problems with either set up but the JR are not nearly as tight. This is not because of gear slop but because the output shafts of the JR do rock. I do not know if it is a function of the quality or location of the bearings or the plastic case.
I thought about installing servo mounts with a shaft bearing but it makes the install much harder.
Stefano
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Old Aug 02, 2013, 02:04 AM
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United States, CA, San Luis Obispo
Joined Aug 2006
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Such a bummer that the MKS servos require a regulator. They would be a real marvel if they ran off of unregulated LiPos like JR and Futaba HV servos.

Stefano, there are output shaft bearings that you can add after the fact. I think Soaring USA sells them. It is just a little G10 plate that has a bearing in it. People who run these seem to be really happy with them.
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Old Aug 02, 2013, 02:21 AM
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United States, CA, Midway City
Joined Dec 2003
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Quote:
Originally Posted by stefanoc2 View Post
I have 398HV all around on a Perfection and MKS all around on another. Because I run Hyperion LIFE the MKS are on individual regulators.
No problems with either set up but the JR are not nearly as tight. This is not because of gear slop but because the output shafts of the JR do rock. I do not know if it is a function of the quality or location of the bearings or the plastic case.
I thought about installing servo mounts with a shaft bearing but it makes the install much harder.
Stefano
Hi Stefano, it was not that the output shafts rocked but because the output spline seems to be a tiny bit smaller than the nylon arm hubs. I tested 4 and 2 had a loose fitting horn. Those same horns were tight on the other 2 and tight on all my 3517s.

I used a piece of potato chip bag placed over the top of the spline and tighten the horn over it. Now there is a tiny, tiny bit of gear slop but livable for ail.
The potato chip bag is a "crunchy" type of plastic with foil like appearance on the inside. It doesn't stretch much so I would think it would be a decent long term solution to the loose hub/spline connection.
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Old Aug 02, 2013, 02:03 PM
launch low, fly high
New Zealand, Hawke's Bay, Havelock North
Joined Dec 2004
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I have used a small circle of the plastic that the horns are in, or tinfoil, on the servo spline prior to pushing on the servo horn. I noticed this rocking some time ago. Of interest is that even without the doily, the slop disappears when the servo horn screw is tightened. I installed the doily for preventative measures "just in case".
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Old Aug 02, 2013, 03:05 PM
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United States, CA, Midway City
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Quote:
Originally Posted by Joe W View Post
I have used a small circle of the plastic that the horns are in, or tinfoil, on the servo spline prior to pushing on the servo horn. I noticed this rocking some time ago. Of interest is that even without the doily, the slop disappears when the servo horn screw is tightened. I installed the doily for preventative measures "just in case".
Yea, the spline issue were also on the 378's. I also did try aluminum foil, but it would tear and I couldn't get enough of the foil around the spline. I also tried the mylar balloons as having 2 young kids I have plenty of these around, but they were too thin. The potato chip bag was perfect! And I mean perfect ! They formed a perfect "cup" around the spline resulting in a very tight fit and a small tear.

I know, I know.. I've got that disease of over thinking everything .
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Old Aug 02, 2013, 03:51 PM
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United States, TX, Houston
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Thank you for the advise. I will try the foil but I am pretty sure that the shaft does rock a little bit because when I put my thumb on top of the shaft of the elevator servo I can see it move forward and aft.
The aftermarket end bearings are great (I purchased a set of 4 from Bob) but of little use if the 398s are set in the plastic servo frames because if the bearings are glued to the top and bottom skin, the servo has to be inserted sliding sideways. That maneuver is not possible given the servo tabs and servo frame configuration. The only chance is to drop in the servo and then try to install the end bearing shaft. The servo well configuration on a Perfection makes this practically impossible.
I want to be clear that I do not have a beef against the 390HV/398HV servos. I have a lot of confidence in them and being able to run them without regulators is a huge plus. I also do not have data on centering ability or energy consumption to compare against the MKS on regulators. I just know that the airplane with the MKS set up has noticeably less slop.
Stefano
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Old Aug 02, 2013, 04:50 PM
War is over (if you want it)
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Thousand Oaks, CA
Joined Mar 2004
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One of the nice things about the JR is that the mounting lugs are only on the sides so you can easily use a 3rd bearing setup and slide right in/out with ease. Stefano, if your frame has material around the "back" of the servo just dremel it out. There's absolutely no reason to have anything back there.
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