Basil Posted September 25 Share Posted September 25 (edited) I wonder if you knowledgeable builders could pass comment about the situation I have encountered while setting up servos by means of a tester( The cheap blue one commonly advertised.) I have more than one.Using 4x AA cell, freshly charged. Some servos react as normal whilst others show all three LEDs on, servo arm random movement, and uncontrollable.. Swap the dry cells for an ESC and Lipo and servo reacts correctly. I have tried various brands but the phenomenon seems to occurs with a particular type supplied by a well known source, that I will not name as other than that I cant fault them. Other types from the same source act correctly . If I have experienced this surely others have. I am currently awaiting the arrival of a more expensive tester. I will do some more tests using it. Bas Edited September 25 by Basil Quote Link to comment Share on other sites More sharing options...
RottenRow Posted September 25 Share Posted September 25 Have you tried another 4 cell battery pack? It sounds as if there a low voltage issue, caused either by the batteries themselves or the connections to them. The battery will probably measure ok off load, but their internal resistance might have risen, causing the voltage to drop under load. It could be worse with some servo types compared to others, depending on the current drawn by them at power up. Brian. Quote Link to comment Share on other sites More sharing options...
Paul De Tourtoulon Posted September 25 Share Posted September 25 I have one of those blue servo testers, and a pile of servos,( only analogic )and I only use nihm 4.8/6v packs and never had that problem Quote Link to comment Share on other sites More sharing options...
kc Posted September 25 Share Posted September 25 1 hour ago, Basil said: Swap the dry cells for an ESC You mean rechargeable I suppose? It's easy to mistake non rechargeable for chargeable in some brands! Quote Link to comment Share on other sites More sharing options...
Gavin Mack Posted September 25 Share Posted September 25 I found some of these cheap servo testers do not have a voltage regulator in them, causing a different servo position with 4.8 or 6V applied. I don't use a servo tester for setting up planes, I always use the receiver going in the plane, on the bench with all servos plugged in to make sue they function together Quote Link to comment Share on other sites More sharing options...
Basil Posted September 25 Author Share Posted September 25 (edited) They are rechargeable types, used in several different battery holders. I like you have to set the neutral point of the arm on the servo initially. Thats all its for. A new type of tester arrives today .Looks like I am the only one effected!!!!!! Bas Edited September 25 by Basil Quote Link to comment Share on other sites More sharing options...
RottenRow Posted September 25 Share Posted September 25 9 minutes ago, Basil said: They are rechargeable types, used in several different battery holders It sounds as though you are using ordinary single domestic AA rechargeable cells, clipped into those (usually) black plastic cell holders. There is every likelihood that your problem lies in this set-up; somewhere there will be a poor connection or a dud cell. The cheapo servo testers are fine for quick tests and centralising servo arms etc. and mine haven't given me any troubles (I always use a 4 cell pack, not 5). They are helpful in diagnosing possible servo issues and also for testing used servos at swap meets etc. Brian. 1 Quote Link to comment Share on other sites More sharing options...
Andy Stephenson Posted September 25 Share Posted September 25 My cheapo servo tester won't work with dry cells in a spring holder and doesn't give a proper centre when used with NiMH pack. When I checked it against my radio, it was about 30% out. I think I might make my own with a pulse length read-out. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted September 25 Share Posted September 25 I only use my servo with a ESC/BEC so I only use a "old" 2s LiPo with a "spare" ESC/BEC with my blue servo tester. It also means I have enough oomph in the LiPo that I can use the servo tester to bench test my motors at low power. Never had any problems with the tester. Quote Link to comment Share on other sites More sharing options...
John Lee Posted September 25 Share Posted September 25 On my blue servo tester I've been using a 4 pack of Enerloops that I date stamped June 2010 when I bought them. Never a problem & the centre is exactly the same as neutral on my Jeti radio. Quote Link to comment Share on other sites More sharing options...
Basil Posted September 26 Author Share Posted September 26 (edited) I have just tested my new tester ' Servo consistency test' black in colour.The problem servo reacts as it should. I can only think that there is something about the construction / electronic design when used with the blue type tester proves to be incompatible. Whist on the subject the new Buwei tester has no instructions. It is supposed to do other tests!!!!. Can anybody advise me about that?. I cant do pictures. Many thanks for your replies, problem solved . Bas Edited September 26 by Basil Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted September 26 Share Posted September 26 I use a blue metal cased servo tester. On some expensive digital servos it jitters a tiny amount for a few seconds then seþles . Only had one occasiob when coild use it to set up servos on a jet wing I had repaired for sombody. Other than that it fine I slso have som chaep testers in a sort of plastic case. These sem fin on most stuff but rarely use them and keep as a stand-by Quote Link to comment Share on other sites More sharing options...
Cuban8 Posted September 26 Share Posted September 26 Almost certainly a bad battery pack - probably a duff cell in amongst the others. Checking on load with a meter will give the game away. Digital servos, as has been said many times are particularly in need of a decent power supply - analogue ones are a little more tollerant, but even so will only accept so much. Cheapo servo testers are fine in my experience - I've had my Hobby King black plastic one for ages and find it indispensible for rough setting up of a model before final adjustments etc with the tranny and when the RX is finally installed. My tester has three settings.........manual i.e controlled from the dial........centre - auto centres the servo...............auto - sweeps the servo from end to end. All very useful I find. Quote Link to comment Share on other sites More sharing options...
Cuban8 Posted September 26 Share Posted September 26 21 hours ago, Gavin Mack said: I found some of these cheap servo testers do not have a voltage regulator in them, causing a different servo position with 4.8 or 6V applied. I don't use a servo tester for setting up planes, I always use the receiver going in the plane, on the bench with all servos plugged in to make sue they function together A very poor design indeed if that is the case. Pulse width and therefore servo positioning should be independent of variations of applied voltage - as with RX outputs. Quote Link to comment Share on other sites More sharing options...
Basil Posted September 26 Author Share Posted September 26 Cuban8, can you explain what is meant by pulse width please. The new tester has a button for 'Pulse width' the figures vary with arm position.Thanks Bas Quote Link to comment Share on other sites More sharing options...
Cuban8 Posted September 26 Share Posted September 26 (edited) Two things to consider. A servo is commanded by the RX to move to the desired position by feeding it with a train of pulses (a heartbeat if you like) that vary in duration i.e on time and off time. The more 'on' time compared to 'off' drives the arm to a certain position and vice versa. Most servos will centre at an input pulse 'on' width of about 1.5 thousands of a second. Variations in that 'on' time will turn the arm one way or the other, usually between 1-2 mS. My servo tester has a switch to select an output pulse time to the servos of either 1.52mS or twice that rate for servos that can work at higher input pulse rates. I just use the standard 1.52mS setting. The internals of the servo will work at the 1.5mS pulse time to drive the motor if it's an analogue device, very much higher if a so called digital servo - probably several hundred times a second compared to around 50 for an analogue servo. What is the servo tester that you have - a look at the manual would be helpful to clarify things. Edited September 26 by Cuban8 Quote Link to comment Share on other sites More sharing options...
Cuban8 Posted September 26 Share Posted September 26 Laptop battery died............. The pulse output selection on your tester that you mention enables you select a number of possibilities by the sound of it. Mine just has two. If you are only using analogue servos select 1.5mS or the equivalent - mine shows 1520 micro seconds which amounts to the same thing. Other outputs will be for digital servos and will not make analogue servos happy by causing them to not work correctly/centre/drive to one end/make a buzzing noise and more than likely cause damage. Quote Link to comment Share on other sites More sharing options...
Phil Green Posted September 26 Share Posted September 26 2 2 Quote Link to comment Share on other sites More sharing options...
Basil Posted September 27 Author Share Posted September 27 Many thanks to all of you that replied. As with most of the equipment supplied that is made in China, no instructions!!!! Bas 1 Quote Link to comment Share on other sites More sharing options...
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