Lighter alternatives to DS95i (tail servo)

[mba83]

Hi all,

I have just installed a DS95i, and the tail finally holds perfectly. I had DS76t previously, and it was OK but it wasn't performing well enough, especially in the wind.

I didn't like the added weight of the DS95i, though - I can totally feel the difference. Are there any lighter alternatives around?

Thanks!

[T3chDad]

Hyperion Atlas DS09GMD. I'm using one on my custom 250 and love it.

Here are a few sources...unfortunately the price almost doubled since I purchased mine....but it's still less than 1/3 the price of the 95i.

All e RC
Skip Miller Models

[Yfbb]

The reason the 95i is so good is because it is more or less a mini servo stuffed into a micro case. it has the torque of a high torque micro servo, yet has enough speed to work on tail. IMHO, you won't find a smaller servo that will perform on its level. Smaller servos may be as fast, but they simply cannot have the same torque.

[Harbormaster]

Originally Posted by Yfbb

The reason the 95i is so good is because it is more or less a mini servo stuffed into a micro case.

I hadn't thought of it that way but I think you're right. Before the 95i was introduced, I remember seeing 250s with a big JR3500G hanging off the boom. They looked pretty comical. People must have been gluing a truck wheel weight in the nose to bring the CG back. (Actually, the plastic-cased 3500G only weighs 20% more than the 95i. It's significantly slower than the 95i too... no wonder so many people bought a 95i for close to $100 when they first came out.)

it has the torque of a high torque micro servo, yet has enough speed to work on tail. IMHO, you won't find a smaller servo that will perform on its level. Smaller servos may be as fast, but they simply cannot have the same torque.

Yeah, the DS76t has a fantastic speed spec but no torque. They must have totally overgeared it to get the speed response at the expense of torque. That's probably why it's failing in wind, when it actually needs some grunt to fight back.

I agree that the DS95i is a heavy chunk of metal hanging off the 250's backside (but I'm willing to live with it since it cast out the demons that were living there). Something with similar electrics but plastic gears and a plastic housing could be 1/3 lighter, I'll bet. Just theorizing... If there's a lighter alternative to the 95i with similar speed and torque specifications, I'd love to hear about it. (And please do quote numbers; "works fantastic for me" is kind of a soft spec. )

[T3chDad]

Originally Posted by Yfbb

The reason the 95i is so good is because it is more or less a mini servo stuffed into a micro case. it has the torque of a high torque micro servo, yet has enough speed to work on tail. IMHO, you won't find a smaller servo that will perform on its level. Smaller servos may be as fast, but they simply cannot have the same torque.

DS95i:
Stall Torque (4.8V) - 1.92 kg-cm
Stall Torque (6V) - 2.40 kg-cm
Speed (4.8V) - 0.047 sec
Speed (6v) - 0.038 sec

Hyperion 09GMD:
Stall Torque (4.8V) - 1.60 kg-cm
Stall Torque (5.5V) - 2.00 kg-cm
Speed (4.8V) - 0.06 sec
Speed (5.5v) - 0.05 sec

At 1/3 the cost and 1/3 the weight...I'd say that's pretty close.

[myxiplx]

I'm looking at a chinese weights upgrade for the 250 tail. It reduces the force needed to move the blades about tenfold, which makes me think a lighter faster servo should still work, even with less torque.

The theory sounds good, need to see what its like in practice.

[Harbormaster]

Go to the servodatabase.com advanced search page and search for:

Modulation: Digital
Speed: Less than .06 sec/60 degrees (95i is .04, 76t is .03)
Weight: Less than 22 grams (the 95i weighs 21)

Note that you can click the column headings to sort by weight, speed, torque, etc.

[Harbormaster]

Originally Posted by T3chDad

At 1/3 the cost and 1/3 the weight...I'd say that's pretty close.

It does look pretty good. Here's the Hyperion specification page for the Atlas DS09-GMD: http://hyperion-world.com/products/product/HP-DS09-GMD

Note that its max rated voltage is 5.5 V. (That's just right for the fixed 5.5 v output of the Talon 25, though.)

The DS09 doesn't fare was well in the comparison at servodatabase.com. There it only has about 1/3 the torque of the 95i. Not sure what to make of that...
http://www.servodatabase.com/compare?servos=999,2101
Looks good at this Hyperion spec page, though!
http://media.hyperion.hk/dn/at-ser/atser-mainspecs.pdf

[Harbormaster]

Originally Posted by myxiplx

I'm looking at a chinese weights upgrade for the 250 tail. It reduces the force needed to move the blades about tenfold, which makes me think a lighter faster servo should still work, even with less torque.

The theory sounds good, need to see what its like in practice.

I have run HEIM JOINT's Chinese weights on a couple of helis (including my 250) for years and am a total believer. Here's a thread: https://www.helifreak.com/showthread.php?t=227978

People argue about them (mostly because they don't understand them, I think), but I measured the current required to drive the servo with and without Chinese weights and it was much lower with the weights, so the servo really is working much less hard. Watch the videos. It's not magic, it's physics. Definitely a must-have on a 250 tail. (I have them on my 450 as well.)

(And if you have an opinion about Chinese weights that you want to share, please be ready to back it up with actual data. )

[JWeber]

The 95i is designed for a 450 size heli. I use one one my Mini Titan. You probably don't need as much torque on the tail of your 250. Unless the tail design is poor.

[Harbormaster]

Originally Posted by JWeber

The 95i is designed for a 450 size heli. I use one one my Mini Titan. You probably don't need as much torque on the tail of your 250. Unless the tail design is poor.

Ha! The tail of the 250 is legendarily problematic (prone to wagging).

If you're interested in learning some 250 lore, the never-ending tail wag thread is stickied at the top of this forum: https://www.helifreak.com/showthread.php?t=269597

The high speed and high torque of the 95i has saved the sanity of many a 250 pilot. It's a bolt-on solution for what can be an absolutely maddening problem. The 95i's only shortcomings are that it's expensive and heavy. If the Hyperion really does have similar performance at lower cost and weight, they'll sell a lot of 'em to 250 guys.

[Harbormaster]

After reading all this, I went ahead and ordered the Hyperion DS 09 GMD (from All e RC because I have always had great service and fast shipping from them) for $30 plus shipping.

After reading the ongoing Lightweight 250 thread here and listening to another pilot I know dissing the 250 for having too much disk loading, I have put my piggy 250 on a diet. If it works, this servo will pare off 13 grams-- about 4% of the heli's weight (enough so I'll have to rebalance to correct the CG).

I'm curious about the "fully programmable" aspect of the Hyperion servo. Servo software?
http://media.hyperion.hk/dn/pc/doc/ATLAS-PROGMAN-EN.pdf

[myxiplx]

Originally Posted by Harbormaster

I have run HEIM JOINT's Chinese weights on a couple of helis (including my 250) for years and am a total believer. Here's a thread: https://www.helifreak.com/showthread.php?t=227978

People argue about them (mostly because they don't understand them, I think), but I measured the current required to drive the servo with and without Chinese weights and it was much lower with the weights, so the servo really is working much less hard. Watch the videos. It's not magic, it's physics. Definitely a must-have on a 250 tail. (I have them on my 450 as well.)

(And if you have an opinion about Chinese weights that you want to share, please be ready to back it up with actual data. )

Yeah, I saw his YouTube video with a torque meter on a 250 tail and was blown away by the difference.

[Besen]

Originally Posted by T3chDad

DS95i:
Stall Torque (4.8V) - 1.92 kg-cm
Stall Torque (6V) - 2.40 kg-cm
Speed (4.8V) - 0.047 sec
Speed (6v) - 0.038 sec

Hyperion 09GMD:
Stall Torque (4.8V) - 1.60 kg-cm
Stall Torque (5.5V) - 2.00 kg-cm
Speed (4.8V) - 0.06 sec
Speed (5.5v) - 0.05 sec

At 1/3 the cost and 1/3 the weight...I'd say that's pretty close.

Just to be clear, it looks like you posted the torque numbers for the DS11-GCB, not the DS09-GMD.

[Yfbb]

Originally Posted by T3chDad

DS95i:
Stall Torque (4.8V) - 1.92 kg-cm
Stall Torque (6V) - 2.40 kg-cm
Speed (4.8V) - 0.047 sec
Speed (6v) - 0.038 sec

Hyperion 09GMD:
Stall Torque (4.8V) - 1.60 kg-cm
Stall Torque (5.5V) - 2.00 kg-cm
Speed (4.8V) - 0.06 sec
Speed (5.5v) - 0.05 sec

At 1/3 the cost and 1/3 the weight...I'd say that's pretty close.

I took a look at the spec sheet: http://media.hyperion.hk/dn/at-ser/atser-mainspecs.pdf. The specs listed for hyperion servo is the holding torque, while the MKS's is the stall torque. Stall torque is how much force it takes to stop the servo from rotating, while the holding torque is how much force it takes to move the horn when it is stationary. Not nearly the same thing. Holding torque is usually significantly stronger than stall torque. In fact, servo database lists the 09GMD's torque as only half the holding torque. Also, speeding up the servo from .05 to .038 is going to take a pretty good hit on the torque. The ds95 cyclic servo is about as fast as the 09GMD, so if the 95i was geared with a 95's gearing, assuming they use the same motor, it would have 3.05kg-cm, and would still be as fast as the 09GMD. Regardless, I feel that a correctly set-up 250 tail shouldn't "need" a 95i to hold properly, and the 09GMD should be enough, heck, I may even try one. However, the 95i is a ton more tail servo than the 09gmd overall. Put both on a 450 tail and it should be fairly evident. Oh, BTW what gyro are you using? I ditched the 3gx for a vbar and my tail never blew out again. The Gyro can make an enormous difference

[Harbormaster]

Originally Posted by Yfbb

I feel that a correctly set-up 250 tail shouldn't "need" a 95i to hold properly

I agree, absolutely, but when you've studied, cogitated, tweaked, tried every tail blade, lubricated, reassembled, measured, modified, after-marketed, etc. etc, and the *#@!% wag reappears yet AGAIN, having the big money, high weight, but damn it fixed it option of the 95i there is a blessed relief.

[Yfbb]

I think that most wag is from binding that occurs when people try to shim out the tail slop. I tried that for two years, and as a result, could never fix the wag. Once I just let the tail be its sloppy self, it finally worked for me. The Ds95i is what my math teacher back in sixth grade would have referred to as "brute forcing", which is just using a lot of effort and power to overcome a problem that could have been resolved with less effort and some better thinking. It is just so powerful that the binding doesn't even stand much of a chance.

[Harbormaster]

Originally Posted by Yfbb

The Ds95i is what my math teacher back in sixth grade would have referred to as "brute forcing", which is just using a lot of effort and power to overcome a problem that could have been resolved with less effort and some better thinking.

The 95i is powerful and also fast, which is equally important when compensating for a mechanically sloppy tail.

It's brute force indeed, but the "better thinking" part of your math teacher's equation was missing from the original design, when Align engineers seemed to have accepted 450-scale tolerances for a heli half the size. You're not brute forcing something that a better setup could fix, you're brute forcing past an inadequate design. (Or so it seems to me, anyway, after fussing with 250s for four years.)

If you read the tail wag thread (all 270+ entries!) stickied at the top of this forum, you'll see that what works for one person (e.g., "Just let it be sloppy") doesn't always work for another, and that a tail that's "fixed" one day may come unfixed after a crash, a component alteration, or a change in the phase of the moon...

[Yfbb]

Originally Posted by Harbormaster

The 95i is powerful and also fast, which is equally important when compensating for a mechanically sloppy tail.

It's brute force indeed, but the "better thinking" part of your math teacher's equation was missing from the original design, when Align engineers seemed to have accepted 450-scale tolerances for a heli half the size. You're not brute forcing something that a better setup could fix, you're brute forcing past an inadequate design. (Or so it seems to me, anyway, after fussing with 250s for four years.)

If you read the tail wag thread (all 270+ entries!) stickied at the top of this forum, you'll see that what works for one person (e.g., "Just let it be sloppy") doesn't always work for another, and that a tail that's "fixed" one day may come unfixed after a crash, a component alteration, or a change in the phase of the moon...

Totally agree. 250 tail=mechanical nightmare.

[Harbormaster]

Originally Posted by Harbormaster

Go to the servodatabase.com advanced search page and search for:

Modulation: Digital
Speed: Less than .06 sec/60 degrees (95i is .04, 76t is .03)
Weight: Less than 22 grams (the 95i weighs 21)

Note that you can click the column headings to sort by weight, speed, torque, etc.

Back on-topic, here's what I found with the search parameters above, listed in order of preference. It looks like the MKS and Hyperion are the only realistic choices unless you're really on a budget, in which case the EMAX units could be an option?

• MKS DS95i .04s 2.4kg/cm 21g $78
• Hyperion DS09-GMD .05s 1.0kg/cm (or more?) 8.4g $30
• E-flite DS76t .03s 0.8 kg/cm 7.6 g $19 Fast but no torque. (servodatabase.com doesn't list the DS76t)
• EMAX ES9257 .05s 2.5 kg/cm 20g $15 Big--35x15x30mm--has speed, torque, heavy as the 95i, but cheap!)
• EMAX ES20D .05s 2.5 kg/cm 22g $15 (Ditto)
• GWS Naro Super .05s 3.0 kg/cm 19g (Failed HK quality control?)
• Gening D905 .05s 1.2 kg/cm 9.8g (No one seems to stock?)

Or maybe a $34 DS95i clone? <edit> Oops, it's a DS95 clone, not a DS95i clone </edit>http://www.himodel.com/radios/KST_21...o_DS115MG.html

So mba83, did all that answer your question?