Lighter alternatives to DS95i (tail servo)

[Harbormaster]

I put the results of my comparison of the MKS and Hyperion in a separate thread here: https://www.helifreak.com/showthread...34#post5968034.

Unfortunately, the Hyperion servo tested way worse than the legendary MKS DS95i. I'm going to give it a try on my heli just because it's so much lighter, but I'm not optimistic.

[Harbormaster]

Originally Posted by Yfbb

I have no specs, but there were two gears in the 95i replacement gearset that were obviously different from the ds95 or kst115 gears. The ratio is decreased, speeding up the servo. Assuming the motor in the 95i and the 95 are the same, the spec change between the gear change should be proportional to the difference between the 95i and 95 specs. I can say it makes my 250's tail feel just about as good as my 450 pro stretch with a 8910a+.

I'm glad it's working for you! Unfortunately, it's hard to make comparisons without speed/torque/cost/size info, you know? Not to be a science Nazi about it, but feel is awfully subjective. But hey, if you've got a 250 with a tail that's not wagging, you're most of the way home.

[Harbormaster]

I replaced the DS95i on my 250 with a Hyperion HP-DS20GMD and took it into the backyard at sunset for a few test hovers.

The center of gravity has definitely moved forward! (The heli is now noticeably out of balance with 14 fewer grams hanging out on the boom.)

The recommended starting tail gain with a Vbar on a 250 is 40. With the DS95i and 3.5 mm ball spacing, I have been able to run the tail gain at 100(!) As soon as the heli got light on the skids at 3500 RPM with the Hyperion, it went into 60 degree 2 Hz oscillations.Obviously, the 100 gain setting wasn't working with the Hyperion at 4 mm ball spacing.

I reduced the tail gain to the recommended setting of 40. At that setting, the heli had the classic 250 wag at 3500 RPM. The wag was better but still noticeable at 4000 RPM.

I worked my way down to a tail gain setting of 15 before it got dark. That flies OK (not great) at 4000 RPM and is almost acceptable at 3500--just a little waggieness. In actual forward sport flight, I think it would be OK. I'm not sure how it will be flipping it around.

So far, I'm not happy with the tail with the Hyperion, and based on years of experience with this heli (back to when it had a flybar, and through four different servos), I'm not hopeful that it's going to get much better. I've been down the road of trying to tweak acceptable performance out of an unacceptable servo before, and I know that "Gee, I sure wish the tail was tighter" feeling too well. But I'll keep trying. It's interesting. And tweaking the Vbar's I gain and P gain settings may help. But...

The good news is that the heli's flying weight is down to only 320 grams now! When I trim some wiring, it will be in the bottom 17%!

[SysCrusher]

I've been real happy with the HSG-5084MG that I'm unwilling to try anything else after going through that much trouble finding something that works. It's still a porker like the DS95i but it's little slower as well. Even then, I haven't had a problem with it running the new weighted tail grips, home made weights and kdbb tail blades.

[Harbormaster]

After a half a dozen test "flights" within the confines of the neighborhood tennis court, I seem to have a Vbar configuration that flies stably with the Hyperion HP-DS20GMD tail servo (much to my surprise) at both 3500 and 4000 RPM. (Good tail performance at 3500 was definitely the more difficult part of the equation.)

From a good DS95i configuration, I:

• Lowered the tail gain from 100(which worked fine with DS95i!) to 20 (40 is the recommended Vbar 250setting)
• Increased tail P gain from the default 80 to 120
• Lowered the tail I gain from the default 60 to 40 <--This appears to be the critical difference
• Moved the ball out from 3.5 mm to 7 mm (favoring speed over torque and resolution) Vbar software says that this gives too big a slider swing, but it works, so...

Lowering the I gain in the Vbar advanced tail settings made the difference. A sustained tail oscillation with an I gain of 60 would simply stop when I switched I gain = 40. (I love being able to switch between four different settings on the Vbar; it's a troubleshooter's/tweaker's dream. )

Later today I'm going to try some more settings at the big field, where there's room to actually fly the thing (which may reveal hidden gremlins, for all I know...)

<edit>My 250 flew great at the field today with its new Hyperion tail servo. The gremlin that revealed itself was a rapid, self-extinguishing oscillation in FFF. I'm confident that reducing the P gain from 120 to 110 will fix that problem. The only problem I see for universal adoption of the Hyperion with the 250 is that I had to fine tune P and I gains, and not every stabilization system allows you to do that, and not everyone knows how (though it's not hard). </edit>

Setup:
Four-year-old (but well maintained) belt-driven 250 with a DFC head conversion, Scorpion HKII-2206-3900KV motor, caseless Vbar mounted on the base plate between the frames, Align carbon main blades, KBDD 40 mm tail blades, Castle Talon 25 ESC

[T3chDad]

Thanks for the report. Good stuff. Now I'm curious now about a DS95i...might have to try one.

[Harbormaster]

Originally Posted by T3chDad

Thanks for the report. Good stuff. Now I'm curious now about a DS95i...might have to try one.

The DS95i is simply awesome: high torque, high speed, and high frame rate. Its only downside is price and weight.

[T3chDad]

Originally Posted by Harbormaster

The DS95i is simply awesome: high torque, high speed, and high frame rate. Its only downside is price and weight.

Well, I pulled the trigger and got one. It will arrive next week. Thanks again for the write-ups and testing.

[Harbormaster]

Originally Posted by T3chDad

Well, I pulled the trigger and got one. It will arrive next week. Thanks again for the write-ups and testing.

Cool. You''ll love it, but if you're putting it on a 250, be ready to rebalance! It's a heavy little sucker. I'd be curious to hear about how it works for you.

(Also remember to reset to 760 uS / 560 Hz.)

Have fun with your hot new servo!

[cpmboy]

any...other..more lightweight MKS's servos for 250 helis?....

[Harbormaster]

Originally Posted by cpmboy

any...other..more lightweight MKS's servos for 250 helis?....

MKS makes great stuff (like the DS95-no-i) but not lightweight. It looks like the only realistic alternatives at this point are the Eflite 76t and the Hyperion.

[mdecker79]

Well I’m far from an expert pilot and have limited flying skills (FFF, lops, roles, flips, Tick tock nose and tail down)

I picked up the DS95i when I felt the tail on my 250 was just too loose with the 3gx. Hard stops were far from crisp and very loose with the heli as a whole just flying very very loose.

When the light weight thread came along I picked up a Talon 15, DS76 cyclic servos along with a DS76t for the tail. As you all know the DS76t is far from a DS95i but it was better than stock. After some flights I still wasn’t in love with the DS76t so I went back to the DS95i.

Reading through this thread mba83 brought up the Chinese weights and the DS76t as an option. I picked up a set from Heim Joint and tried them with the DS95i and frankly I couldn’t tell the difference in flight performance because of the high torque.

So last night I figured I would swap out the DS95i for the DS76t with the Chinese weights and drop a good 12g’s for an AUW of 308 on my 250.

Well today I took the DS76t out in a very windy day with winds at about 5mph or 10mph with gusts to 15mph every now and then. As you all know the wind makes the heli fly even more loosely then it does when it’s not windy. BUT I have to say… I can’t tell the difference between the DS95i and the DS76t with the Chinese weights in the wind. The heli still felt extremely locked in and it did not feel lose what so ever. Fast tail stops were very precise with no wag and I couldn’t be happier. Also the tail did not drift or loosen up during slow flips like it used to and I’m all around VERY happy with the result.

So much so I might even think of selling the DS95i but I'm still going to test further.

[Harbormaster]

Originally Posted by mdecker79

Reading through this thread mba83 brought up the Chinese weights and the DS76t as an option. I picked up a set from Heim Joint and tried them with the DS95i and frankly I couldn’t tell the difference in flight performance because of the high torque.

I think you're right and that you make a great point there: the DS95i is so powerful that it can mask the effect of the weights--they never really get a chance to show their stuff!

I can’t tell the difference between the DS95i and the DS76t with the Chinese weights in the wind. The heli still felt extremely locked in and it did not feel lose what so ever. Fast tail stops were very precise with no wag and I couldn’t be happier. Also the tail did not drift or loosen up during slow roles like it used to and I’m all around VERY happy with the result.

So much so I might even think of selling the DS95i but I'm still going to test further.

Very interesting report. Thanks.

[myxiplx]

Great update, good to hear that worked in practice as well as in theory :-)

[mba83]

Thanks for the info! Where can I purchase the chinese weights to try? Thanks

[Harbormaster]

Originally Posted by mba83

Thanks for the info! Where can I purchase the chinese weights to try? Thanks

Send a private message to HEIM JOINT asking him for info. He does not seem to have a website or anything like that.

[T3chDad]

I received my DS95i yesterday. It looks very pretty all silver and red!

Unfortunately, it will be several days before I will be able to play with it. I also have a brand new DX9 that's still in the box since I brought it home from the store a week ago. Hopefully, real life will settle down by next week and I can play with my new toys.

[mba83]

Originally Posted by Harbormaster

Send a private message to HEIM JOINT asking him for info. He does not seem to have a website or anything like that.

Thanks. Looks like it will be over $20 shipped. Perhaps it would be wiser to add a few bucks and buy a Hyperion servo instead? Decisions decisions...

[Harbormaster]

Originally Posted by mba83

Thanks. Looks like it will be over $20 shipped. Perhaps it would be wiser to add a few bucks and buy a Hyperion servo instead? Decisions decisions...

Easy decision. Buy both! It's working for me.

Seriously, the weights help to compensate for the lack of torque in the servo. It's a great combination.

[Harbormaster]

Originally Posted by T3chDad

I received my DS95i yesterday. It looks very pretty all silver and red!

They are beautiful little devices.