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Member postings for Brian Parker

Here is a list of all the postings Brian Parker has made in our forums. Click on a thread name to jump to the thread.

Thread: Motor Kv - the truth
26/05/2010 20:23:04
Erfolg,
Have a look at the ‘part throttle efficiency’ thread for further traces.
I don’t fully understand the relationships/patterns within the traces but do find them compellingly attractive.
 It’s a pity that you are unable to post Camille’s data.
26/05/2010 14:45:11

 

 

 

 

 

These are traces From low idle through to max throttle. I posted these a while ago on a thread looking at throttle efficiency.
 

 
 

Two Traces from two windings.

Thread: Metal to metal interference
21/05/2010 14:13:33
BEB,
 Interesting link.
The maths within the link serves to emphasise the harmonics caused by non-linear produced interference.

Thread: Motor Kv - the truth
21/05/2010 12:06:12
This Month, in a rival publication, Alasdair Sutherland comments on Props and Static Stalled Props.
Funny old world.
Thread: Metal to metal interference
21/05/2010 12:00:00
The interference is the non- linear reaction between the metal push rod and metal arm creating a ‘diode’ effect and causing passive intermodulation due to the close proximity to the receiver antenna.
Oil, dirt, damp, corrosion or even possibly lightly contacting surfaces being the candidate.
 This is why the problem can ‘come and go’ or not exist at all in some installations.
 Before plastic drain pipes, corroded metal gutters and associated metal work could cause communication problems between ‘stations’. This was known as the rusty bolt effect or more properly as PIPs (Passive Intermodulation Products).
Our 2.4Ghz systems will be immune.
Thread: Motor Kv - the truth
18/05/2010 20:13:56
Erfolg,
We are probably 'guilty victims' of using relatively simple explanations for complex subjects.
 Off thread, but referring to your weight on a spring. If you hang the spring onto a spring balance, give the weight a pull and then let go you have an experiment in inertia as the weight accelerates and decelerates as it comes to rest at the top and bottom of its stroke (much the same as the reciprocating parts of an engine).
 (Kinetic energy snippet. A rocket loses most of its mass in the burnt fuel and will receive in return more kinetic energy as a proportion the chemical energy than will the ejected burning gasses.)
18/05/2010 08:56:44
John is correct.
 An accelerating flywheel (prop) is storing kinetic energy. A decelerating flywheel is releasing energy. At a constant speed a flywheel is neither storing nor releasing kinetic energy.
 If we accept that the brushless motor, at a constant speed will maintain (unlike an IC engine) a constant velocity throughout each revolution the prop will behave as a flywheel at a constant speed.
 Just how much kinetic energy can be stored in a prop given its small mean radius, low mass and the fact that mass is not concentrated at the prop tips (flywheel rim?)?
Not a lot I expect (but am not quite geeky enough to work it out for myself).

Thread: Puffed Up Lipos
17/05/2010 20:36:52

You guys must have plenty of disposable cash.
 Why throw away perfectly good cells?
Just remove the puffed cells, test the remaining cells and if all OK, use them to build new packs.
 I had this happen to me with a couple of BRC HiModel 3S. One outer cell puffing on both batteries (not the inner cells). I put it down (probably) to stress due to the Velcro straps I was using to hold the battery in position.
No further problems after more than 12 months use configured as 2S and a revised fixing.
Thread: Motor Kv - the truth
13/05/2010 10:13:22
Under the static tests we have airflow over the blades but we have no forward velocity.
The lift vector is tilted against rotation and the thrust force is transferred to resisting rotation rather than providing forward motion.
 Is that not a technically stalled situation?
 (The APC Engineering site seems to confirm this).
 Also ref. the Eagle Tree Graph above it will show no change as we are simply transferring forces.
12/05/2010 14:26:16
Technically, are not all props stalled during static testing at whatever the RPM? (Unless the tests are conducted in a wind tunnel).
 In flight, at a given air speed the Prop will 'unstall' because the lift/drag ratio of the prop is increasing in the moving air.
Thread: help with petrol engine problem please
11/05/2010 11:18:04

What’s the idle speed?
 These engines need an idle speed of at least 1600rpm for a clean pickup and return to idle.
Thread: Motor Kv - the truth
11/05/2010 10:58:35
My tu’pence worth on Zinger verses APC.
Its not in the wood its all in APC's distortion and drag.
 The drag of a rotating prop resists the rotation of the drive shaft, producing a torque reaction.
 Maximum rotational speed is reached when torque reaction equals shaft torque.
 Lower the drag (through distortion) and rotational speed will increase for a given power input.
This may or may not increase the efficiency (Thrust *Velocity/airflow factor).
06/05/2010 13:17:49
Timbo,
I would have expected the no load RPM to be slightly lower than ‘spec’ as you are calculating from pack volts rather than ESC output volts.
 We can (?) assume that the wire gauge and number of windings are standard, so either the stated Kv figure is incorrect or perhaps tolerance in the ESC's back EMF sensing is allowing higher RPM.
Thread: Re-run of a thread I started 2 to three years ago updated!(Running an engine on water)
31/03/2010 10:06:11
To heavy to post.
Thread: Diesel v Glow
29/03/2010 19:54:09
An alterative name for the Compression Ignition engine is the Constant Pressure Engine Due to the fact that the pressure of the burning gases is almost constant throughout the combustion cycle.
Thread: Re-run of a thread I started 2 to three years ago updated!(Running an engine on water)
29/03/2010 19:44:20
 
Experimented with water injection in the ‘60s.
 But still needed to get a proper job.
Thread: Spark ignition-radio interference.
28/03/2010 15:41:42
Peter,
So your gizmo has ‘transistorised’ the points.
 This will in fact reduce arcing as stated by Larry.  The circuit may already contain a capacitor but no harm to try an additional capacitor in parallel.
 Make sure all the 0volt cables are to a common connection to maintain a low impedance 'earth'.
 Most of these vintage coils are designed for 3 volt operation. ie. two 'dry' cells. Three fully charged Ni-MH cells are in excess of this voltage. It will give you fat spark at the plug but will  increase the electromagnet field (and interference) and also increase the coil loading.
 It might be worth just trying a couple of alkaline cells, this may solve the interference problem.
 You can also reduce the Ni-MH voltage with a zener diode across the supply (but check the current rating). Also make sure the cells have a large enough capacity to prevent voltage fluctuation.
 A simple regulator can be constructed by using a 317 type regulator IC to reduce the voltage to 3volts but you will need to increase the cell count or use a Lipo.
 I would not advise using rectifier diodes to reduce the voltage because of lack of regulation when the cells start to discharge with use.
 You could of course try it without the transistorised unit, if you have not already done so, just to check that this is not the cause of your problem.
Good luck

Edited By Brian Parker on 28/03/2010 15:43:24

Thread: backwards engine running
27/03/2010 11:39:45
Turbo oil seal failure results in oil, under pressure, being fed directly into the inlet manifold to be consumed by the engine until the oil pressure ceases as the oil runs out or the uncontrolled engine explodes.
Thread: Spark ignition-radio interference.
26/03/2010 20:04:00
The ‘condenser’ is actually a capacitor and your ‘gizmo’ is intended to do the same job (I assume).
 When the contacts ‘break’ the current still tries to flow and causes arcing. When a capacitor is fitted across the contacts it receives a charge as the contacts break thus reducing the arcing and also ensures a rapid collapse of the coil magnetic field (better spark). When fully charged the capacitor discharges through the primary windings.
The collapsing magnetic field causes lines of force to cut through both the primary and secondary windings, the induced primary voltage could reach 100 volts, the secondary voltage gives your spark and is several thousand volts.
The arcing, the magnetic forces and the induced voltages are your enemy.
The ignition circuit should be completely separate from the RC circuit with its own battery ie. completely isolated from the RC system.
All cables need to be as short as possible. Keep everything close to the engine and screen it all off, foil is OK.
 Your fitted micro switch servo control needs to preserve this isolation. An opto switch is the safest.
A Capacitor of .1uf will be OK provided it is rated above the primary induced voltage, ie. 250volts.
What exactly is your ‘gizmo’?
 Are you using ‘ModelAero’ type coils?
 
A bit lengthy, hope it helps.
26/03/2010 14:37:40
With 2.4Ghz and CDI ignition I have tried to induce a malfunction by placing both an unshielded coil (running at 250volt primary) and a CDI circuit board in direct contact with the receiver, the servos and the cabling in turn.
 The system performed perfectly, (confirmed by a scope trace).
2.4Ghz  plus CDI is the way to go.
 However, before you spend your money, and if not already fitted, you might like to try a capacitor across the CB contacts plus another  from the switch side of the coil to the engine ground.
I take it that you are using a separate battery for the Ignition and that it is electrically isolated from the RC.
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