Steve Hargreaves - Moderator Posted November 2, 2011 Share Posted November 2, 2011 Just thinking aloud really.....you see very little in the way of reviews & comment regarding the muscle power in our models namely servos.... There are literally hundreds of different types & makes out there some of which seem to be utter rubbish whilst others offer amazing performance & quality at incredible pricing but sorting the wheat from the chaff takes some doing.... I have many different servos.....some good some not so good but until they actually land on your bench how do you know whats good & what isn't? I recently bought 4 servos for a new project & they are very good for the price (about £5 each)....smooth, very powerful & good centring but they have a little bit of backlash in the gear train which translates as a bit of slop in the control surface. Is the old adage of you get what you pay for true here?? I had a couple of Hitec HS81MGs that failed & cost me a model...I think I paid about £17 each for them. And then I have some HS81MG "equivalents" from HK which cost about £6 each & they have been faultless..... I guess a database or review of all the servos out there would be a mammoth task, not least because the intended use of a servo is so important. A particular servo might be perfect for controlling the rudder of your Super 60 but might not perform so well on the tail rotor of a 90 powered 3D helicopter.... I'd be interested in the thoughts of others.... Quote Link to comment Share on other sites More sharing options...
Ben B Posted November 2, 2011 Share Posted November 2, 2011 I totally agree. One of the other mags has been running a month by month "servo selection" guide but really it's just a description- we need proper tests and feedback. Just listing all the servos from a particular manafacturer isn't that enlightening. A databse would be an excellent idea. Perhaps we could even vote via the poll option on which servo we'd recommend for a particular type / size of plane. The results could then be tabulated into a "recommended servo guide" broken down into size of model, model type and price range. e.g. Small 3D model:Budget:Mid-range:Expensive: Small fast / delta model: Budget: etc etc etc There's an online calculator that lets you work out your kg/cm requirements based on airspeed, control surface size / throws etc but even when you know that there's a mind-boggling number to chose from. Analog vs digital, coreless vs brushless etc etc Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted November 2, 2011 Share Posted November 2, 2011 My experience has been slightly different. Normally I invest in "name brand" servos - usually Futaba or Hi-Tec. Once I was lured into buying a more "economy" brand on the promise that they really were good. I was dissapointed, with two of them stripping gears and nearly costing me a model, despite the fact that the flight loads etc. were well within the servo in question's spec. Indeed I replaced them with HS82MG's which had the same spec as those that failed and they have been in there for over two yeasrs with many flights under their belt and have shown no sign of failing. In fact I struggle to remember a Futaba or a HiTec servo failure that wasn't ultimately my fault. So I retreated back to my well tried behaviour! Now don't get me wrong, I'm sure that there are good cheaper servos out there to be had - but like you I don't know which ones. And even if somone recommends them, which was the case with the "economy servos" I tried, it seems it doesn't really mean much BEB Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted November 2, 2011 Author Share Posted November 2, 2011 Posted by Biggles' Elder Brother - Moderator on 02/11/2011 12:11:02: Now don't get me wrong, I'm sure that there are good cheaper servos out there to be had - but like you I don't know which ones. And even if somone recommends them, which was the case with the "economy servos" I tried, it seems it doesn't really mean much BEB This is exactly the problem David...I have bought "highly recommended" servos & found them disappointing & have bought servos that got poor reviews & found them excellent.... I have to say that I have always found Futaba servos to be excellent...I have some that are nearly 20 years old & are still going great but they aren't cheap...especially if you start looking at digitals or higher powered units.....as I said maybe you do get what you pay for.... Quote Link to comment Share on other sites More sharing options...
Lee Smalley Posted November 2, 2011 Share Posted November 2, 2011 same here BEB, i needed 6 servos for big glider used well known budget servos that i had had before, that were very good, i ordered 8 of them and when connected up 5 were shocking juddering about the center totally different end points and centers i fitted the others that were relatively good and used one i had in stock, there performance over the next 6 months was such that i had to rip them out and fit HS85BB s they have been faultless since, if you buy budget servos the quality control is generally pants, some good some bad some terrible, personally, its the last time i will ever buy budget servos, just not worth the hassle Quote Link to comment Share on other sites More sharing options...
Erfolg Posted November 2, 2011 Share Posted November 2, 2011 The problem with budget servos in my usage is that they are in the smaller sizes. Generally 9g. If they have plastic gears, they are liable to strip, if the linkage is exposed and could be snagged for example on grass. As all modellers, I have had expensive servos fail. Again in my case it has been stripped gears. The most memorable was a glider which suddenly became what I thought was uncontrollable in pitch. I did manage to land, in one piece. On examination I found that about 3 teeth had stripped. No rational explanation. With cheaper servos, on occasion I have found that after landing, that a shock load has damaged the gear train. In my opinion it is ailerons which are most vulnerable, with no UC, onto grass. I now try to have the linkage on the upper surface, removing the linkage from the grass tufts. In general I have no problems, as such. Although I totally accept, that digital servos are a must for high performance gliders, where precision is most beneficial on flying surfaces, to extract model performance and predictability. Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted November 2, 2011 Share Posted November 2, 2011 Almost exclusively use HiTec, and the occasional Fuby unit.Only exception is for the odd non-flight-critical thing like light switching, bomb drop etc. Quote Link to comment Share on other sites More sharing options...
Reno Racer Posted November 2, 2011 Share Posted November 2, 2011 I agree with the chart, but fear it would be enornmous, once you start including all the HK type servos that no-one has heard of before. I normally stick with HITEC, in fact I use HS311 standard servos in all my sports models and warbirds upto 60 size. Small electric 30 3D I use HS225s. I have got 6 of these badboys in my Revolver 61, which needs more servo power than HS311s can provide. They are noisier than the HITECs, but very powerful and have been reliable so far, once you get past the fact that they are orange! For small stuff and foamies, I generaly use those 9g blue Turnigy HXT900 Servos. Quote Link to comment Share on other sites More sharing options...
Lee Smalley Posted November 2, 2011 Share Posted November 2, 2011 you buy an aircraft worth over 200 pounds and you shove servos in costing about 4 quid each ...please!!!!!! if they give up the ghost and cost you a beautiful aircraft, dont dare moan. Quote Link to comment Share on other sites More sharing options...
Reno Racer Posted November 2, 2011 Share Posted November 2, 2011 Just becuase there cheap doesn't make them crap. I've had more brand servos fail over the years, recently had a Futaba servo fail in an aileron on my 91 size Decathlon. I've had absolutely no issues with these servos, they centre well and accurate and powerful. I must admitt, I was hesitant, and tried them in a sport hack first to see how they'd perform, but the've been good. P.S £120 aircraft for me in the US. Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted November 2, 2011 Share Posted November 2, 2011 Posted by Christian Ackroyd on 02/11/2011 13:18:22:Just becuase there cheap doesn't make them crap. I've had more brand servos fail over the years, recently had a Futaba servo fail in an aileron on my 91 size Decathlon. I've had absolutely no issues with these servos, they centre well and accurate and powerful. I must admitt, I was hesitant, and tried them in a sport hack first to see how they'd perform, but the've been good. P.S £120 aircraft for me in the US. Touche Quote Link to comment Share on other sites More sharing options...
Erfolg Posted November 2, 2011 Share Posted November 2, 2011 The problem with quoting specific brands and reference numbers is that ignores duty required for model type. Some have touched on the issue, that in my opinion both servo and model need considering and discussing as a combination. So may be the discussion should revolve around groups, such as small electric, medium IC, Very Large Models, as well as recognising that some competition type gliders, need high forces at times to control the model.. It may be worth noting that IC models give the carbon track a hammering, when compared to electric models. Quote Link to comment Share on other sites More sharing options...
Andy Green Posted November 2, 2011 Share Posted November 2, 2011 I bought 4 servos from a reputable on line servo supplier, they were noisy with very high quiecent current drain. This review sums them up. There are also some useful tips for what to look for when reviewing a servo. I now only use brand name servos. Andy Edited By Andy Green on 02/11/2011 13:51:49 Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted November 2, 2011 Author Share Posted November 2, 2011 Posted by Christian Ackroyd on 02/11/2011 12:55:44: I have got 6 of these badboys in my Revolver 61, which needs more servo power than HS311s can provide. They are noisier than the HITECs, but very powerful and have been reliable so far, once you get past the fact that they are orange! For small stuff and foamies, I generaly use those 9g blue Turnigy HXT900 Servos. Interesting Christian....I spotted these but discounted them as too cheap....I mean a 9kg dual BB servo with metal gears for 4 pounds....I thought they must be rubbish!!! A big for the HXT900s from me too....great servo & only $2 a throw...amazing value!! Its probably worth noting that it isn't just the UK & USA who utilise low cost Chinese manufacturing either....my very old Futaba servos say "Made in Japan"......middle aged servos say "Made in Taiwan" & my newest say "Made in China" & lets face it...if you were a production controller for Futaba looking to cut costs you might talk to a Chinese factory who was....ooh I don't know....perhaps already making servos........ I don't mean to say that all servos come out of the same factory but I bet there is a lot of cross over & rebadging goes on..... Quote Link to comment Share on other sites More sharing options...
Lee Smalley Posted November 2, 2011 Share Posted November 2, 2011 ok 120 quid for you in us and yet you use 4$ servos well thats your choice and your aircraft, as i said don't moan if the worst happens, i thought you would agree tim you like cheap as well !! i have been flying for over 20 years iand i can count on one hand the branded servos i have had fail (two actually and they were failures out of the box) so what your doing with them i am not quite sure to have loads of failures, maybe time will tell on the longevity of these servos in your model, but would you have the guts to come back if they do fail and hold your hands up ??? everyone is different but i would not risk such a nice model and what must be about 300$ worth of aircraft in the air on 4$ servos, but thats my choice, yours is different, i find it odd you swear by hitec stuff but then put something that is even cheaper than a 311 in something you prize, ahh well as for a chart well i am not sure it will work, the quality control from china can be flaky to say the least and one batch of servos may well perform quite well, so the reviewer writes positively about these cheap servos, the next batch may well be quite poor and fail on all those people that bought them on the back of said review ... can you imagine the stick the reviewer and or mag would get in that instance !!! Quote Link to comment Share on other sites More sharing options...
GONZO Posted November 2, 2011 Share Posted November 2, 2011 You may find THIS SERVO DATA BASE of interest. THIS SERVO TORQUE CALCULATOR or THIS OTHER SERVO TORQUE CALCULATOR may be of use. Also, these PEAK SERVO CURRENT TESTS show just how hard the BEC in the ESC can end up being pushed when using some micro servos. HTH Quote Link to comment Share on other sites More sharing options...
Vecchio Austriaco Posted November 2, 2011 Share Posted November 2, 2011 I have bad experience with small cheap servos - mainly the accuracy and sometimes the gears are the problem. Best experience with Hitec HS55, HS81 and HS82MG, I use the 81s in several models (but I have always a spare gear set as the gear brakes easily) I use also several Spektrum DS 821 - precise, reasonable strong but also plastic gear. Means perfect for an electric plane up to a larger Sebart (Angel 50) but I am not sure for glow or petrol. On my glow Extra I use only metal gear servos (HS82MG for everything but the rudder which is using a Graupner low cost digital standard size servo). The reason are the strong vibrations coming from the engine. Going petrol (my next Extra) I will use only standard size metal gear servos. (Will be Graupner DES 806) Who has seen the vibrations from a reasonable size petrol engine will know why. Cheers VA Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted November 2, 2011 Author Share Posted November 2, 2011 Excellent info there Gonzo.......it seems what I seek is already available.....now...if we can all rush off & add our reviews for each servo the database will be complete... Quote Link to comment Share on other sites More sharing options...
Vecchio Austriaco Posted November 2, 2011 Share Posted November 2, 2011 Gonzales, nice database, I miss the brand Graupner but may be they are not in the narket at your place. I like also the work about the peak current, would be interresting also for bigger servos. Cheers VA Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted November 2, 2011 Share Posted November 2, 2011 This subject has of course, been discussed, and links to most of the charts, and calculators etc, as well as real world testing been done before. Such as this old thread. And this. Another..... In fact a quick search entry produced 6 PAGES of links to servo related enquiries on this forum alone. I may be biased of course but I think the testing I did with an eagle tree logger ONBOARD an actual model, in flight, gives a better real world picture of servo current consumption than bench testing with a scope. Personally, I think most people way overestimate the power used by the average club model. Quote Link to comment Share on other sites More sharing options...
Reno Racer Posted November 2, 2011 Share Posted November 2, 2011 Lee, I'm open to suggestions, I'd be interested on what you would recommend, without been too expensive. Analogue is fine for me and I have also converted the model from one servo on the elevator to 2. I recently looked into some HobbyPeople branded servos that were retailing at $8. I am lucky to have some good renouned US flyers and model designers at my club; RCKen from RCUniverse is our club president, he did a review on these servos, turns out inside they are rebranded Futaba S3001s - exactly the same inside and out, just a different label, so suspect made in the same chinese factory, but 1/2 the price. Quote Link to comment Share on other sites More sharing options...
Lee Smalley Posted November 2, 2011 Share Posted November 2, 2011 I have no recommendations christian but here is what I do and I will give some examples when reviewing the zlin I trust hitec so I searched the hitec range for servos with a bit more grunt and hs 485hb were just the ticket at 13 quid each for my db spit I will use hs 645 for the critical surfaces but at 25quid each I did not want to fit them to everything so I have tried some alturn servos 750 mg I have purchased a few and they live on the rudder for both my big petrol aerobats they will stay there for many months being shook to bits and I will evaluate them after that, if still good they will be used on the flaps and rudder on my spit at 16 pounds each they are a worth while saving if they are reliable, for my moulded typhoon glider I asked around and chose savox 255 at 15 quid each still not mega cheap but cheaper than Hyperion servos at 40 quid, my own wAy of doing it would be to buy a few and put them on rudder and throttle and give them 12 months, it will be the vibration that will kill them if anything.As an aside I have ordered a few of the hobby king servos and I will be testing them and then dismanteling them to check build quality, but I must stress my main concern with servos of these type is the quality control they get afforded, 1 good 1 not so Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted November 2, 2011 Share Posted November 2, 2011 Posted by Tim Mackey on 02/11/2011 16:37:40: Personally, I think most people way overestimate the power used by the average club model. I would totally agree with that. Most of the time servos are working against the "blow back" force. If you calculate that - using a few simple assumptions - you'll find out its extremely small, equivalent to maybe less than 1/30th of the maximum torque the servo can exert. But there is a reason for this. We want our control surfaces - and the associated linkage - to be very stiff indeed to resist any dynamic loading such as flutter inducing forces etc. For that reason we need a large margin between what the servo needs to exert in normal control usage and what it could exert in extremis. All this means that 99.9% of the time our servos are only drawing a fraction of the maximum current they would need if they were called on to exert their maximum force. And because they are so stiff, instabilities such as flutter are hardly ever allowed to grow to the extent that the servo would be called upon to deliver its ultimate power. So, its a bit of a strange situation really - effectively servos are hardly ever required to "give of their best" because they have the capability to "give of their best" if you see what I mean! They nip any excursions in the bud because they are so stiff and they are stiff because they have a reserve of torque. BEB Quote Link to comment Share on other sites More sharing options...
Erfolg Posted November 3, 2011 Share Posted November 3, 2011 BEB How about posting the link to the calculation and assumptions you made in a previous thread. At a practical level, I do remind myself, that in the 70's most servos had a similar performance to most 9g type servos, and many people flew successfully 0.60 glow models, with them. I am not suggesting that common servos used today are massively over specified, I am suggesting that it is not necessary to be obsessive about selecting adequate/appropriate servos. Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted November 3, 2011 Share Posted November 3, 2011 Hi Erfolg, All will be revealed hopefully! Firstly, I'm sure David wont mind me telling you that I cover a similar topic in answer to a reader's letter that should be published in the next mag. That gives some details but still a bit sketchy. But secondly, we are putting together plans for another aerodynamics series for the mag at present and this topic is high up the list of features! So I'll be able to give it the space it deserves there I think. Hope that helps BEB Quote Link to comment Share on other sites More sharing options...
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