Frank Skilbeck Posted July 24, 2009 Share Posted July 24, 2009 Posted by Tony Stein on 24/07/2009 20:28:58: I have to say that piccy proves to be a very convincing argument. The graph I'll need to study before I properly understand what it's telling me. (Is the 35-42 motor the same as the 35-30?)The plane is 20 oz all-up weight so at 80watts per lb that's 100 watts required. If I get what's going on then at a draw of 20 Amps and, on an 11.V battery that's 222 watts or 120% over what I need?I think I need a smaller prop .Thanks for the help it's much appreciated. I will get to grips with this eventually I promise. In the meantime I thank my lucky stars that I found this site.... Sorry program didn't list the 35-30, 35-42 is basically same kv but rated for a higher current. Don't try restricting throttle end point ot 75% some ESC autocalibrate on the end points so you couldn't guarentee you would pull to many amps on an 8 x 6, 8 x 4 seems the way to go. Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted July 24, 2009 Share Posted July 24, 2009 Posted by Tony Stein on 24/07/2009 20:45:23:Hi Austen,Thanks for this. I don't think I'd have got this intuitively. To me, a bigger kv would mean it would turn a bigger prop easier... . I'm slowly getting to grips..So here's a question...If I set my transmitter to max out the throttle at say, 75%, will this safely limit the load on the ESC even if I leave the 8x6 prop on?T Not really no. ESCs are actually working much harder at low and middle throttle settings than when at WOT - when they are basically just like a straight through connection, feeding full power constantly to the motor.... no rapid switching involved.Any of the proprietory wattmeters will be fine - Puffin models do a nice one for reasonable money. Properly used, it could save its own cost first time out. A point not really mentioned in detail is about your battery choice. More cells = more volts =more amps. Obviously the reverse is true, but whereas this reduction in volts may well bring your current down to manageable levels, your RPM will drop a lot too. Now this may not be advisable, depending on the model.In the same vein, changing props to alter the load on the motor, and consequently also reducing current consumption will affect the way the model flies. Reducing the diameter of a prop will make a big difference to static thrust, and reducing pitch will drop the top speed .... Neither trait may be what you need Edited By Timbo - Moderator on 24/07/2009 22:43:04 Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted July 24, 2009 Share Posted July 24, 2009 Posted by austen rover on 24/07/2009 20:37:05:tony its mainly the size of prop you use that effects amps,the kv rating of your motor will effect this also a 800kv motor for example will turn bigger prop with less effort producing less amps ,a higher 2000kv would turn a smaller prop faster or say a EDF , a 1100kv motor is a good middle ground motor and so id use a smaller prop to reduce amps . amps x volts = watts for example 15amps x 10.5V (3s battery under load) =157.5 watts If you wanted more power but wanted to keep the amps the same you could use a higher voltage battery( if your motor and esc are rated to do so) 15a x 14V (4s batteryunder load)=210watts What should be stressed here though is that a prop change would be needed to meet that target. Simply changing a 3s to a 4s battery on the same prop will actually result in much higher amps and higher volts...so watts will be much higher than stated here, and the aim of keeping the same current will not be met. Prop down to arrive at the target watts ( 210 ) and only then will the amps stay at 15 ( 210W / 14V = 15 Amps ) Edited By Timbo - Moderator on 24/07/2009 23:04:42 Quote Link to comment Share on other sites More sharing options...
Myron Beaumont Posted July 24, 2009 Share Posted July 24, 2009 Timbo I was wondering when you'd come in with what you've been explaining for yonks Quote Link to comment Share on other sites More sharing options...
TonyS Posted July 25, 2009 Author Share Posted July 25, 2009 The glimmer of comprehension is turning into a full dawn! It seems a lot to take in but now I think I understand. What really did it was the comment about switching. It's not right to think of the ESC like a tap which you can close a little to restrict flow and slow the motor. A tap doesn't do any real work when half closed. An ESC, from what I'm reading, is actually working to manage the flow. Thinking of it like this it's easy to understand how it starts to heat up - a bigger ESC can handle the work better ( gets less of a sweat on!). Makes me start to wonder what almost all of the ESCs I've ever seen are plastic shrink wrapped. Surely this is one of the worst ways of allowing the working elements to keep cool? I guess it's down to price. Is there a manufacturer that makes a 'premium' product ESC with a finned metal jacket or one specifically designed to allow the internals to keep cool? Quote Link to comment Share on other sites More sharing options...
ken anderson. Posted July 25, 2009 Share Posted July 25, 2009 http://www.conceptmodels.co.uk/index.htm hello again tony---this lad is good, for reasonable price's and good stuff...and the essential Free advice..........and of course the' piece de reisistance'...he's in the north east........... ken anderson... Quote Link to comment Share on other sites More sharing options...
TonyS Posted July 25, 2009 Author Share Posted July 25, 2009 Hi Ken,Thanks for the link - which is now bookmarked. I like the step by step on how to choose the right motor ESC battery combo and, like you said, his packages seem to be well priced. Fingers crossed for a good day of flying.... Quote Link to comment Share on other sites More sharing options...
TonyS Posted July 25, 2009 Author Share Posted July 25, 2009 Another quick thought......Apart from the price issue, is there any downside to simply sticking a massive ESC on every model (given the relatively small differences in weight). I.E if there are real risks of over-working an 18, 20 or 25 amp ESC why not just buy a load of 100Amp ESC's and be done with any worry? Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted July 25, 2009 Share Posted July 25, 2009 Posted by Tony Stein on 25/07/2009 08:06:17:Another quick thought......Apart from the price issue, is there any downside to simply sticking a massive ESC on every model (given the relatively small differences in weight). I.E if there are real risks of over-working an 18, 20 or 25 amp ESC why not just buy a load of 100Amp ESC's and be done with any worry? You could do that by all means, but many of the very large units are quite costly, and they do get very heavy once your in the 100A+ category. Also, many of the very large units dont have a BEC on board, so might not suit some smaller models, but otherwise there is no reason to not "go big". Premium gear like Jeti and Hacker etc do have finned heatsinks to dissipate heat on some versions, and one or two even have built in fans.Some people simply fit their own fans ( ex PC CPU fans are ideal )... but TBH its a bit OTT for most stuff. A decent headroom on capacity is the best way, and I only have 2 x models in my entire fleet which even need the ESC in the breeeze to keep em happy - the rest are buried inside the fus somewhere Quote Link to comment Share on other sites More sharing options...
TonyS Posted July 25, 2009 Author Share Posted July 25, 2009 Thanks Timbo.You'll have gathered I've never seen a 100 amp ESC in the flesh!I'm going to dig out a 35 Amp ESC which should easily do what I want in the E-Zee - then I won't need to modify the model to stick in air scoops and outlets etcI'm a bit concerned about the F-9F I'm also off to fly which has the ESC well and truly buried but the EDF really screams when it's running - still, It all came virtually ready to fly so I guess the boys that put it together knew what they were doing (or am I being too optimistic..........?) Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted July 25, 2009 Share Posted July 25, 2009 Possibly .However, remember what I said about ESC when running flat out ( which EDFs are most of the time ) the esc will not be actually working very hard at all. Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted July 25, 2009 Share Posted July 25, 2009 Here you are, you poor deprived thing... a picture of a 100A+ ESC alongside a servo for scale. This thing weighs a 1/4lb and is good for 100A constant, and 120A bursts. Note that although a 3 wire Rx cable is attached, there is NO BEC unit, and the red +ve wire of that cable is actually not connected to anything, The black and white wires carry the battery ground (-ve ) and throttle command signals, and is still plugged into the throttle channel port. This typoe of unit requires a separate power supply to the radio gear, via any spare port on the Rx. Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted July 25, 2009 Share Posted July 25, 2009 PS... you might like to fill a little in on your profile page by now Tony, or the replies may start thinning out Doing so allows me and others to quickly check whether you are online at the time, and therefore we know whether to expect a posting for instance. Apart from that, we are a nosy lot and want to know all your grisly details LOL Quote Link to comment Share on other sites More sharing options...
TonyS Posted July 25, 2009 Author Share Posted July 25, 2009 Right Timbo,Off I go to the details page>Little update on today....The Simply E-Zee had no problems with the motor/ESC combo that weren't totally overshadowed by my hamfisted use of elevator which resulted in the wings folding and the whole thing burying itself in the ground from around 250 feet.The F-9F Panther was beautiful and flew quickly and smoothly right up to the moment when I put it into a spin that frankly I was too inexperienced to handle so now I'm looking for a new fuselage and wing.My home made flying wing was a winner - it looks like it was made in the dark by someone with no knowledge of aero engineering , wearing boxing gloves and having had a bottle of vodka. It's only problem was it was slightly underpowered but luckily, I have a motor / ESC from an old Simply E-Zee that will do just perfectly If I can work out how to put pics on the sight I'll share....Now, to the profile page....T Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted July 25, 2009 Share Posted July 25, 2009 Oh dear, sounds like a bad day Tony There is a tutorial on posting pictures on threads, HERE. Quote Link to comment Share on other sites More sharing options...
TonyS Posted July 25, 2009 Author Share Posted July 25, 2009 Actually Tim, It's a pretty normal day's flying for me....Is there a tutorial on fixing planes - could be more useful... Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted July 25, 2009 Share Posted July 25, 2009 last months mag.... two part article by our very own guru Peter miller - all about repairing crashed models. Quote Link to comment Share on other sites More sharing options...
Merlin spit Posted July 25, 2009 Share Posted July 25, 2009 tony ,i told you timbo was your man for electric ,last months mag was very helpful for me toEdited By austen rover on 25/07/2009 18:22:51 Quote Link to comment Share on other sites More sharing options...
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