TonyS Posted October 8, 2009 Share Posted October 8, 2009 Hi, I've taken delivery of the Hoffman Magnetics Wild Beast motor Specifications Kv - 4880 R (ohms) - 0.007 Weight - 130 grams Application -70mmEDF Battery - 3s-4s lipo 1700 WATTS. and an Overlander, 3700 mAh, 4S 35C battery and now I need to find a good 125A ESC to round off the package.Anyone any recommendations? Quote Link to comment Share on other sites More sharing options...
Bruce Richards Posted October 8, 2009 Share Posted October 8, 2009 Tony,what fan are you planning to use with that? It looks like a mighty powerful set up and you will be working that battery very hard. What model is it going in? Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted October 8, 2009 Share Posted October 8, 2009 Thats what I thought too.... Thats a big Kv for a 70mm fan, and if you are going to get high Wattage out of it, then the current ( especially on a 3s ) would be enormous.Wtihout knowing your expected current draw, its hard to suggest an ESC - I have a 100A one here going spare if thats any good ? Quote Link to comment Share on other sites More sharing options...
TonyS Posted October 8, 2009 Author Share Posted October 8, 2009 Hi Chaps, It's going with the recommended Wemotec 480 mini fan Pro in my Yak 23 . From what I've read on the Hoffman site the fan should be fine but they recommend a 25 % margin of safety on the 100A ESC so 125A. Can't imagine they'll be long flight times on WOT. My main concern was a very reliable hand launch and the ability to handle any slight over-runs on weight (one of my past problems with building however this model is bang on the money so far). Quote Link to comment Share on other sites More sharing options...
Bruce Richards Posted October 8, 2009 Share Posted October 8, 2009 This looks like good value NOT. I can only find one 125A ESC buy Castle creations. I have no experience at these high currents so I can't be much help. Sorry. Quote Link to comment Share on other sites More sharing options...
Bruce Richards Posted October 8, 2009 Share Posted October 8, 2009 What about this 150A burst. I have found the smaller Emax ESCs to be very good. Quote Link to comment Share on other sites More sharing options...
TonyS Posted October 8, 2009 Author Share Posted October 8, 2009 Thanks Timbo for the offer of the ESC and Bruce for the links. his is harder than I thought. I'll worry about this later I think - for now it will be good to see the plane finished which is now taking longer due to creeping self doubt and dithering..Shame as I was really motoring. Still. One of the immediate probs is that without a receiver connected I can't be sure of the 'at rest positions' for the servo arms on my aileron servos which will be built in and therefore not adjustable after the wing is finished. The problem is that without the ESC I can't think of how to connect up the Rx and servos. Can I simply plug the servos into any old spare port on another model to find the 'at rest positions? Quote Link to comment Share on other sites More sharing options...
Bruce Richards Posted October 8, 2009 Share Posted October 8, 2009 Sort of.You need to plug the servos into a channel that is controlled by the TX probably 1,2,4 would be good. the power up the Tx and power up the RX. Make sure the trims on the Tx are cantered and the servo should also be centred. The other method is to use a servo tester which I understand is a very useful piece of kit. I could never justify the cost. Quote Link to comment Share on other sites More sharing options...
Tom Foreman Posted October 8, 2009 Share Posted October 8, 2009 I just plug everything into a spare receiver and then power it up using a rx battery which came with the radio set. 1700W sounds a lot of power for this model, plus your only going to get a minute or two flight time. My 4s1p 3700 powered EDF's run at about 60A WOT and with throttle management I only get four and a half minutes flight time with enough reserve power for waiting to land if the strip is busy (tip don't launch last when everyone else is flying). Ton will know better but I would think with all the wing area your not going to need more than 800W for an easy hand launch, or you could always cross over to the dark side and bungee like me, however I do have a broken Sniper to fix after I tried bungee launching using a dolley on long grass and no head wind Tom Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted October 8, 2009 Share Posted October 8, 2009 Why not simply plug in a receiver battery to power up for setting up? Quote Link to comment Share on other sites More sharing options...
TonyS Posted October 9, 2009 Author Share Posted October 9, 2009 Thanks Tom, useful stuff. It'll be interesting to see what the run times are like. Timbo, you're quite right sometimes the simple solutions just pass me by......... Now, where did I put that Rx battery..? Quote Link to comment Share on other sites More sharing options...
TonyS Posted October 9, 2009 Author Share Posted October 9, 2009 Bruce, Tom, Timbo et al, Interestingly, the LiPo I'm using is just a shade under the weight of the NiCads this model was designed for. The max AUW for the model per the design spec is 1200g or 2.6lb and given that I intend to give it a coat of glass I'm guessing I'll be at the max weight.The Motor supposedly gives a max 4lb of thrust on a 4S which is quite a solid ratio of just over 1.5 : 1 thrust to weight.Do you think an 800W motor would deliver the necessary thrust? To get anything like useful hand-launch performance I'd have figured on a min of 1:1.How could I calculate the thrust from the Wemotec 480 Minifan from an 800W motor?(I appreciate this is possibly drifting slightly off-topic but what the heck it's part of the same conversation ....) Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted October 9, 2009 Share Posted October 9, 2009 Wel I use a home built thrust stand to measure static thrust...you may have seen it in times / threads gone by. Of course, in the air things change, but it was designed to compare things in like for like scenarios and worked very well - certainly proved the efficiency of the midi-fan rotor over pretty much everything esle. Whether your model will happily fly 9 and hand launch ) on 800 Watts depends on many factors, and I fear your only way of really finding out is to try it. I have a lightweight EDF Sabre which happily and very easily hand launches on a PWR of just 112 Watts P/lb, and weighs in at 1.1lbs, so I guess thats around 1:1 ratio.There are various software calculators around the WWW which may give an estimate of your set up. Havent looked at it lately, but maybe motorcalc caters for fans ? Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted October 9, 2009 Share Posted October 9, 2009 THIS used to be the thread, but for some reason it doesnt always link correctly - I will get the tech guys to have a look at the problem...if it doesnt work, use the search box on the main poage, and enter "fan testing" Quote Link to comment Share on other sites More sharing options...
John Cole Posted October 9, 2009 Share Posted October 9, 2009 How does your planned motor / esc/ LiPo setup match with the plan or kit recommendations? Quote Link to comment Share on other sites More sharing options...
TonyS Posted October 9, 2009 Author Share Posted October 9, 2009 Hi John, It doesn't as the kit was designed in the days of NiCads so I'm pretty much flying by the seat of my pants (no pun intended) T Quote Link to comment Share on other sites More sharing options...
John Cole Posted October 9, 2009 Share Posted October 9, 2009 Based on looking at a couple of websites and the comments from others I would be quite surprised if you need 1700 W for a 2.6 lb model (650 watts per pound), or that your motor will draw the current you are thinking of when driving a small fan: back-EMF will push the current down. Indeed, I fancy that 1700 W on a 68 mm will burst it! Here's a quote from the rcgroups.com forum: "Kontronic 480-37 in Minifan on 12 FAUP 1950 cells takes 580 watts HOC to give measured 37 ounces of thrust, rpm around 40,000. After 20 seconds 490 watts to give 32 ounces. This is probably about the maximum the fan will take reliably" The hot motor recommended for the kit draws 35 A max continuous, and the recommended ESC has a max. surge current of 50A (see Kontronics USA) I would be inclined to test the set up with the largest ESC you currently have, and measure the current draw. Unloading in the air will increase revs and hence back-EMF, and therefore the current draw will fall in flight, so t's a conservative test. Then look for an ESC with 150% capacity of your measurement. If in this test you get close to the burst-limit of the existing ESC as you open the throttle, you STOP! Quote Link to comment Share on other sites More sharing options...
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