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Peter Wood

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  1. Big argument, sorry, debate, at the field this afternoon. When the motor and battery have to be some distance apart, should the ESC be closer to the battery or to the motor? Anyone have the definitive answer and reasoning?
  2. Timbo - After recovering the plane we ran the motors at full power on the ground again with the same batteries with no signs of distress. At that time I had not figured out the likely cause so we did not check then out at 2/3 throttle. So the esc's were not burnt out and it was not the BEC's cutting in. We did extensive checks on the radio which was OK. The spec for the ESC's states that there is a thermal cutout at 105deg which reduces power to 30%. As it was very hot on Saturday and the ESC's were behind the motor ie in its warmed air, the overheating explanation seems the most probable.   Chris raises a good point about twin batteries. It had been suggested to me before I flew the model that I should couple the batteries and motors together. I put it off because of the hassle of making two X leads. I don't think it contributed to the crash but will be making them for the future to ensure that both ESC's are seeing the same voltage and thus reducing the chances of one BEC kicking in before the other.   I thought electric twins were supposed to be easy!!   Peter
  3. Steve and Chris   Thanks for the replies. I have been doing more research since last night  and came across an article on the Giantcod site.   http://www.giantcod.co.uk/forum/viewtopic.php?f=15&t=689   Now this is pretty heavy stuff and I don't claim to understand it all but what I have taken from the paper is that the switching cycles vary with the throttle setting and as Chris says the heat is generated when the FET's are switching.   However the most relevant info in the article was the following ---   The worst case scenario for an ESC is to run at around 2/3 throttle setting. In this case, the transistors are carrying a heavy load and switching on and off several times per cycle, with no time to rest between cycles. It is during operation in this range that the ESC will get the hottest.   This was exactly the condition when the plane flicked to one side and into a spin.   Remarkably the plane is repairable and I will be fitting it with 60amp esc's.   Peter
  4. Is there a linear relationship between the amount of heat generated by an ESC and the throttle setting? That is does the esc generate more heat at 10% throttle than 90% say because it is chopping the current more often? Last week I purchased second hand a brand new unflown CMP C160 complete with motors and esc's. A check on current showed both motors pulling 40+amps - ample power I thought. Take off was uneventful and after gaining height I cut power to about 70%. Very quickly thereafter the plane flicked violently to the right into a spin. I recovered and climbed again. A power off stall test showed no untoward behaviour but on opening up to part throttle it flicked again. Eventually the inevitable happened and I could not recover the spin. On investigating the remains I discovered the esc were only rated at 30 amps. HOWEVER they ran quite happily at full throttle for several minutes pulling 40amps with no signs of distress. I suspect therefore that they were cutting out at 70% throttle because of the extra heat generated. Is this a feasible explanation?
  5. Dave    I bought a Warco WM180 about three years ago which is of a similar spec to the C3. I had no engineering experience and it was a very steep learning curve but here are some things I have found out the hard way.   The first thing to recognise is that these mini lathes and 7x10 type lathes have their limitations. Because they are not as robust as bigger lathes they have their limitations in terms of accuracy. It still amazes me that a 20mm steel bar can bend under turning forces. Nonetheless as you gain experience you can take steps to minimize the problem.    Also the smaller the machine, the smaller the task it can undertake. I burnt out the motor on mine when trying to turn down a piece of ali from 110 mm to 70mm. I got impatient with the time it was taking and started taking bigger cuts at higher speed until the inevitable happened. As I say, recognise their limitations.   Secondly I would not get hung up on what screw threads can be cut. I have still not used this facility (a) because it is difficult and (b) because most threads you will want to cut are easier with taps and dies.   A four jaw chuck should come as standard. It is essential for working on anything other than bar or circular items.   A set of cutting tools including a parting tool is essential and I would add a quick change tool post with two or three holders. It is a pain changing tools when you have to adjust the height with shims. With a QCT the tool remains in its own holder which is set at the corect height so accuracy is maintained.   Finally I would buy a Dial Guage or Dial Test Indicator ( see Chronos). Almost essential for accurately setting up work. The former is cheaper and more versatile but the DTI is more sensitive.   A final thought. Making things on the lathe is quite addictive. I now spend as much time making gadgets and stationary steam engines as I do building planes. As a result I soon bought a milling machine and cannot resist buying all sorts of extras. Beware!!   Peter        
  6. 66   IC Sport/scale Elec Sport Slope   Ignoring an abortive attempt at a rubber kit in my early teens started seriously at 30 with a Veron glider (forgotten name)
  7. Nobby - I don't know about the motors but CD drives contain some tiny powerful magnets around the laser head which are quite useful for securing hatches etc. Also the rods carrying the laser head are precision ground and can be used as replacement motor shafts. Bit of a fag to dismantle the drive but worth salvaging. Peter
  8. I have read David's books and articles avidly over the years. I learnt to fly on a DB Tyro. So when he came over to ask about my model at a Flair open day a few years ago I felt like I was being approached by royalty. In fact he was a super down to earth guy who was so easy to talk to he could have been a member of my own club. Super chap. Get well soon.
  9. 1. Mode2 2. Cambridgeshire 3. SE Berkshire 4. Self taught
  10. OK - Thanks David   Andy - wish I had thought of that on 1 Dec - I might have had 10 accounts!!
  11. Some time ago I had difficulty logging on to my account, probably around the time I changed ISP and changed e-mail address. In frustration I registered again but of course my original id was taken. Consequently I ended up with a new account and a second identity. I have now found my original identity details and can access the first account. Is it possible to merge the accounts or do I have to delete one?
  12. I was recently building a Precedent Stampe wing. The plan only gave the port wing and the instructions suggested that for the starboard wing the plan should be taped  to a window and  the outline traced on the back of the plan or alternatively spray it with WD40 to make it semi transparent. I took the plan along to a local printing company and for £1.50 had a mirror image printed. Much simpler.
  13. Not bought kits from them but have had Li-pos motors and ESC's and they are great. Delivery is remarkable. On one occasion I placed order on Tues night and it was delivered Fri morning!  Just remember that the exchange rate has dropped markedly in recent months and they are not as cheap as they were.
  14. Professor I have added another photo to illustrate a couple of points. Sorry about the confusing background - I will try to take a better shot when I have a bit more time.. The flaps and slats are both fully deployed - you can see them better in this shot. The main undercarriage is as per plan ie one piece held on by a couple of saddle clamps under the fuselage. In practice there seems to be very little flexing of the wire, the main movement up and down movement in this arrangement being a rocking motion on the 'dampers'. I have thought of building a new u/c in two halves, each half fixed to the fuselage by longitudinal pivots. However in this case all the vertical movement would be handled by the 'damper' springs and I doubt if they are strong enough. It will be next week before I can fly again when I will experiment with a more forward c/g and possibily mixing down ele into throttle. In the meantime I have to find a better way of fixing the cockpit roof. I made the centre section removable and held on by a couple of magnets. However the propwash through the firewall fuel pipe holes blows it off as soon as I throttle up. A few more magnets I think. Peter
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