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Member postings for Steve Hargreaves - Moderator

Here is a list of all the postings Steve Hargreaves - Moderator has made in our forums. Click on a thread name to jump to the thread.

Thread: inverter generators
04/11/2018 20:10:15
Posted by Chris Walby on 03/11/2018 22:08:16:

  • Leisure battery will need to be charged and brought along in the car (bit of aggravation, but at least you can start you car to go home!) They look expensive typically £100 per 50Ah of capacity, but give you the flexibility to charge any of your flight batteries. Or spend the money on some more flight batteries

110Ah Leisure battery here for just under £75 delivered if you choose this route.... **LINK**

Thread: Saito FA40 Performance Increase
04/11/2018 17:46:03

Would using fuel with a higher nitro content be worth considering?

Expensive, yes, but I think any "tuning" would come at a significant cost & in my experience tuned engines usually come with a trade off. Yes you might get more power but at the expense of reliability or a good idle or poor mid range throttle response or something else that makes the engine that bit les pleasant to handle.

The manufacturers generally know most about their products & try & make them the best they can be in all areas.

Just my 2p wink 2

Thread: Any Electric Only Groups or Clubs in the North West
03/11/2018 17:46:18

I'm intrigued...why Electric Only Eric?

Most clubs these days have a healthy mix of both IC & Electric power....wink 2

Thread: Fitting battery first time lipo battery for nitro engine
28/10/2018 14:20:37

Thread locked....no point running two threads on the same question... wink 2

Thread: ABC pinch on new motor
28/10/2018 14:13:58

Warming it up won't hurt & may well help a bit.....use a hot air gun to get the cylinder nice & hot then start as usual. Short fast runs just slightly rich with a cooling off period in between are the best way. Don't run it rich & slow.....it needs to get up to temp as fast as possible....

Thread: they are still at it.(PayPal).
25/10/2018 21:43:48

+1...since we bought our phone with BTs Call Guardian I don't think a single spam call has come through. They still call...I can see them on the register but they don't get through.

If you're plagued by these calls buy one....worth every penny. thumbs up

Thread: Need to Change Kit Specified Prop?
25/10/2018 21:38:38

Hi Chris...that motor ticks a lot of boxes...the max current & power are all about there but I think I would go for the 1000kv version. It will take a bit more current & power & it's always useful to have a little headroom with electric components...running anything flat out or close to flat out will inevitably shorten its life.

The main reason though is the kv.....1000 rpm per volt will give us a something over 10,000 rpm at full throttle & that "feels" about right for the size of model we are talking about....the 800kv motor will spin at little over the 8000rpm mark which feels a bit slow for the model to me. For sure you can increase the prop size & this will increase the thrust generated & the power produced by the motor but IMHO a slightly smaller prop spinning at a high-ish speed will suit the model best....something around a 9x5 should do it.

The thing is to get somewhere in the ball park using the maths & then fine tune it with the size/pitch of the prop used to get the right current/power/flying characteristics. You quickly find that in electric flight you need a lot of props of slightly different size on hand for that final testing.

Ooo & another thing....buy a wattmeter....you'll need it to make sure all the parameters are within the limits of the components & that nothing is going to melt.

Thread: Boeing 737?
21/10/2018 20:18:59

A Boeing 737 would be a pretty advanced model to fly under radio control. If powered by model gas turbines it would have to be pretty large & expensive too. The vast majority of models flown in this country tend to be single engined, prop driven. Much simpler & cheaper. wink 2

Thread: Hi
21/10/2018 20:15:11

Hi Darragh....Welcome to the forum......

RC Flying is huge hobby....any tips or recommendations about what exactly? How to fly? What model to start with? What radio gear?..... Give us a clue.....teeth 2

There are some good threads here to get you started

Thread: Need to Change Kit Specified Prop?
21/10/2018 20:01:52

Ooo OK a little bigger than I was expecting & quite large for a Speed 400 hence the gearbox & 10" prop....

OK let's begin....

The well worn formula says we need around 100 watts per lb of all up weight (apologies for the mixed units but's a simple "rule of thumb"; for a Warbird I might be tempted to go a little bit higher so we'll "round up" when it comes to the maths....if we use a LiPo & a brushless motor in place of the Speed 400 & gearbox I think it will come out a good bit lighter anyway.

800g is about 28 oz or 1 3/4lbs so 1.75 x 100 equals 175 watts (BTW that's a lot more than your Speed 400 was ever going to give you.....wink 2). A 3 cell (3S) LiPo battery will be ideal for this sort of application….a 3S LiPo is nominally 11.1V but all batteries sag a bit under load so lets say it’s holding 10V as that makes the maths easier.

Applying Ohms law (or a derivative of it anyway) we know that Power in watts equals Voltage in er Volts x Current in Amps….rearrange that slightly & substitute the numbers we get Current equals Power (175W) divided by Voltage (10V) so our full power current is 17.5A. We can use this figure to determine the size of speed controller we need…a 20A or a 25A unit will be ideal. Similarly this gives us a good idea of battery size. Personally I like to use a discharge rate of around 10x the capacity of the battery (commonly known as 10C) as this equates to around 6 minutes of full throttle flying to fully discharge the battery (60 minutes divided by 10 equals 6 mins). Now two points to bear in mind here 1) we never fly at full throttle all the time & 2) you should never fully discharge a LiPo…aim for around 80% to keep your batteries happy. This two factors mean that our 6 minutes of full throttle flying will equate to around 8-10 minutes of general flying with a bit left to keep the battery happy.

So…if 10 x the battery capacity equals 17.5A then the battery capacity must be 1.75Ah or more commonly 1750mAh. That’s a bit of an unusual size so probably look for 1800mAh or you could go down to 1500mAh…obviously a smaller battery will offer less duration but will also be a little lighter.

We now have the size of ESC (20-25A) & the battery (a 3S 1500-1800mAh unit) defined so we are well on the way to a working set up…to the most difficult bit…the motor. We already know a bit about it…we know it must be able to handle a 3S battery & a current of around 18-20A (it’s wise not to spec your electrical components to their very maximum ratings….always leave a little bit of headroom) so what else do we need?

We need…… The kV figure… This is probably the hardest thing to get your head around. It represents the rpm the motor will spin at per 1V applied so a 1000kV motor will spin at 1,000rpm if we apply 1V or 10,000 rpm if we apply 10V. So how do we know what to go for? Difficult one to answer….experience does play quite a large part here as does the type of model. A large slow flying model will need a slowly turning large prop (low kV) whilst a small fast model will want a small fast turning prop (high kV). The thing to remember about the kV figure is that this is the speed your motor will always try & turn at; it is in effect the speed it is designed to run at & is a function of number of windings, number of magnets & a few other things that don’t concern us here) so whatever sized prop you fit, the motor will always try & reach it’s design speed. If we have a high kV motor & fit a big prop this represents a high load for the motor & it will draw more & more current until it reaches its design speed or melts & dies in the process. Similarly if we fit a small prop to a low kV motor this represents a low load so the motor will reach its design speed no problem but won’t generate much thrust in the process.

Back to your Spitfire then…..originally designed for a 10” prop because that was the only way the poor thing would stagger off the ground with it’s Speed 400 up front but I think we would be better going for a 9” prop & spin it a little faster…..lets aim for about 9,000 rpm. 9,000 rpm divided by our battery voltage (10V remember) gives us a kV figure of 900.

And that’s pretty much it….we need a 20-25A ESC….a 1500-1800mAh 3S LiPo & a 20A motor with a 900kV. Pop a 9x5 or 9x6 prop on the front (check with a Wattmeter & go up or down a little in diameter/pitch to get the desired current) & you’ll have a very nice Spitfire with a pretty good turn of speed.

I'm sure you'll have a few questions after reading that lot so fire away & I'll try & answer them for you...thumbs up

21/10/2018 18:18:19

Does that 800g include the battery?

Not familiar with the model but I'm guessing it's around the mid 30s (inches) wingspan?

21/10/2018 17:38:16

You don't need to match the original Chris...start from first principles & we can talk you through it.....lets start with the model....what is it & what is the expected all up weight?

21/10/2018 16:56:26

IMHO you should replace the lot with a brushless set up Chris.....wink 2

Brushed motors were never very good for electric flight but there wasn't an alternative...now there is I don't see any point struggling on with something that wasn't very good in the first place....

Just my 2p-worth smiley

Thread: Puller for a prop driver
21/10/2018 16:42:44

As above...I bought one of these...... **LINK**

Worked very well....thumbs up

Thread: coming back
14/10/2018 20:45:51

Welcome back Phil....it's like a disease...once a modeller always a modeller....thumbs up

Thread: Returning after decades so not total Newbie!
14/10/2018 12:19:13

Sounds too low to me Chris.....LiPos don't like being run down to much below 3V per cell.

ESCs are so cheap these days surely best to just buy a new one?

Thread: Margaret's health
14/10/2018 12:17:10

So sad to hear of your loss OT....

So great to hear about the new arrival......

Thread: Help with first time electrics
13/10/2018 12:38:10

Is it the Mini Super Stan? The 48" version?

I built one a few years ago so can happily provide details of what I used.....if you type Mini Super into the search box a few threads appear.....

But if you are going down the electric route then the sooner you get started with your own calculations the better...wink 2...follow BEBs advice & see how far you get...ask lots of questions & before long it will all slot into place....

To paraphrase a famous saying "Give a man an electric set up & he will fly one model....teach him how to calculate his own electric set ups & soon he will have a hangar full...." teeth 2

Thread: Electric Junior 60 Watts Per Pound
06/10/2018 15:48:04

I had a similar experience some years ago with my Mini Tyro which has a similar power to weight ratio to your Junior 60... see here ..... & spookily came up with a similar figure..20 watts per pound

Thread: New Laser engines. What do you want?
19/09/2018 18:32:54

At the request of the OP this thread has been closed.

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