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help needed with first conversion

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rcaddict21/12/2015 07:45:54
508 forum posts
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hi guys

so I am now been bitten with the leccy bug I want to try a conversion now

I have a precedent T180 which currently has a MDS 40 on it

I was thinking of a turnigy G46 but there are 3 different choices 420,550, & 670kv - which one should I go for

also what prop

Bob Cotsford21/12/2015 09:08:23
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Now that will depend on your choice of battery - how many cells are you planning on running?

Dave Hopkin21/12/2015 09:59:46
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The prop size will also play a major part in the choice..... all the Turnigy G46's are rated for 4 to 5s lipps so the lower the Kv rating the bigger prop you will need to get the same power developed

The 670kv one is rated at 741W, the other two are rated at 925W (on 5S Lipos)

I have one of the 550Kv on a Hobbyking stick 1500 using 4S lipo with a 14z8 (if memory serves) and it drags it round happily at under half throttle

Geoff Sleath21/12/2015 11:39:24
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Well anything will be better than an MDS 40 in my personal experience!

I have a G46 670 kv that's slated for installation in a Dennis Bryany 1/6 scale SE5a (56" ws IIRC) and I'm intending to run it on 4S LiPo on 12x6 or perhaps 13x6. I haven't run it yet so I don't know but in any case you need at least a 60 amp esc or perhaps 80 to be super safe. A wattmeter and a few props will be your best friends.

To some extent battery size and weight depend on getting the CoG in the right place. I converted an 84" ws Ezee Pezee trainer and ended up having to fit 2 x 4S 3600 maH LiPos just to get the model to balance. So there'll be a bit of suck it and see but it should be fairly straight forward.

Geoff

Steve Hargreaves - Moderator21/12/2015 12:41:09
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I sense we need to go right back to basics here so lets start at the beginning.....

What weight is the model as it stands (ie c/w engine, tank etc)...? I'm guessing at around 5lbs but please tell us. From here we can work out how many watts are needed (based on 100 watts per lb or so) & guide you to a suitable motor/ESC/battery to fly the model & maybe convert you to the sparky side....wink 2

rcaddict21/12/2015 17:11:57
508 forum posts
14 photos

model is 6.5lb

I was hoping to use a 4s

Geoff - I agree about the MDS but this little engine is a little sweety

PatMc21/12/2015 18:02:52
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Assuming 6.5lb the RTF weight - if you go for 4s the 670kv motor would be the best bet, a 60A ESC should suit it on a 13 - 14" prop. As Geoff mentioned, the battery capacity is best decided by using it's weight to achieve the required cg. Minimum capacity for a normal duration flights would probably be 3600 - 4000mAH.

Steve Hargreaves - Moderator21/12/2015 19:31:06
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OK 6.5lbs...so you'll need 650watts or so to make it fly nicely.....a 4S battery will give you about 13.5 volts under load so 650 divided by 13.5 equals 48A or so....

This means you need an esc capable of at least 50A...make it 60A to be on the safe side.

Now...you'll probably have something like an 11" prop on the MDS spinning at 10-11000 rpm so if we aim for a similar set up on electric we know we won't run into ground clearance issues. 10000 divided by 13.5 equals 740 give or take.....this would be out kv figure.

If you look for a motor able to take 55-60A with a kv of around 740 or so & team that with an 11x6 or 11x7 prop then success is pretty much guaranteed.....if you have enough ground clearance then Pats 670kv motor on a bigger (13" prop would be even better. Remember to test the final set up with a wattmeter won't you?

Battery wise something around the 3600-4000mAh mark should be ideal....

Hope that helps.....post again if you have more questions...

PatMc21/12/2015 19:55:28
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Steve this model won't need 100W/lb. I fly my Magnatilla on 4s with a 12x6 pulling just inder 31A for 460W (75W/lb). Model weighs a couple of oz over 6Lb with old 4s 4000 15C lipos & has more than enough power for aerobatics are ever likely to be tried on a T180.

Steve Hargreaves - Moderator22/12/2015 08:54:09
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You may well be right Pat.....650W is nearly 1 horsepower & I doubt very much the MDS40 is putting out anything like that kind of power.....

I am often guilty of overpowering my models....embarrassed....

Tony Richardson22/12/2015 10:15:55
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Better to be overpowered than IN the ground laugh

PatMc22/12/2015 10:35:02
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Posted by Steve Hargreaves - Moderator on 22/12/2015 08:54:09:

I am often guilty of overpowering my models....embarrassed....

Something a lot of people do, Steve. Trouble is they forget that the throttle stick isn't a binary control, then they have to resort to messing about with downthrust. wink 2

PatMc22/12/2015 10:35:59
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Posted by Tony Richardson on 22/12/2015 10:15:55:

Better to be overpowered than IN the ground laugh

More models crash through being overpowered than underpowered.

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