HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Dec 04, 2001, 09:52 AM
LT
Registered User
Stavern, Norway
Joined Jun 2001
143 Posts
Short flight time on MPX Twin Star

I have a Multiplex Twin Star using the stock 400 size motors, stock Gunter props, 7xRC2000 with Kontronik Easy3000 regulator.
I think I have seen several reports on this forum mentioning 8 minutes flying time on similar setups. I am only able to get 4.

I have two batterypacks and both give same results. The packs have seen less than 20 flights each, but are a few years old. Both packs have been cycled 3-4 times after taken out of storage.

Both motors was have been run in under water (gained close to 1000 rpm static), and than timed by turning endbell 2mm (5/64inch) opposite direction of prop rotation (rpm gain not tach'ed). axels are straight, and I have not noted any sparking.

Have I overdone the timing, or are the reported 8 minutes flight time optimistic?

Regards
LT is offline Find More Posts by LT
Last edited by LT; Dec 04, 2001 at 09:54 AM.
Reply With Quote
Sign up now
to remove ads between posts
Old Dec 04, 2001, 10:26 AM
Registered User
Bill Glover's Avatar
United Kingdom, Bracknell
Joined Nov 2000
11,554 Posts
Only 4 minutes run time on 2000 mAh cells would mean an average current draw of 30A!

A 6V 400 on 7 cells with a Gunther prop doesn't pull anywhere near 15A on full throttle, so something is wrong.

Either your packs are not fully charged (what charger?), they have degraded and the capacity is less than 2000 mAh, or you have seriously messed up your motors and the current draw is way more than it should be (can you measure it?).

You mention cycling the packs, how did you do it and did you get a capacity figure from this?

You should get at least 8-10 mins flight time. With 8x2400 (higher current but more capacity) I think I used to set the timer for 12 mins (before I switched to a geared setup). And that was with the weight/drag of a trike u/c.
Bill Glover is offline Find More Posts by Bill Glover
Reply With Quote
Old Dec 04, 2001, 11:06 AM
Master
ChrisP's Avatar
Weilbach, Germany
Joined May 2001
2,467 Posts
I have 8x2400's, stock motors and stock props and can get 19 - 20 minute flights if I play the throttle.
ChrisP is offline Find More Posts by ChrisP
Reply With Quote
Old Dec 04, 2001, 11:16 AM
Registered User
Larry Dudeck's Avatar
Williamsville, NY, USA
Joined Sep 2000
4,466 Posts
With the stock Twin Star set up and a 7x2400 pack I have stretched the air time to 14 minutes, powered the whole time.

But I find 14 minutes of lazy circles sort of boring so I have upped the amps a little and set my timer for 12 minutes, always landing before the BEC kicks in.

I also have a 7x2000 'Gigapower' pack (Sanyo rejects as far as I can tell). I limit the run time of this pack to 8 minutes. My 7x1700 pack of good Sanyo's is a 10 minute flight.

My flying field is a treacherous place to land what with 3 baseball diamonds with fences and backstops, two or three soccer fields, bleachers, portapotties, etc., etc. So I always cut short the flight time. This is no place to attempt a no power landing.

Great place to fly, though.

I suspect your packs are shot.

Also, have you checked the orientation of the props? Did you somehow mount them backwards?
Larry Dudeck is offline Find More Posts by Larry Dudeck
Reply With Quote
Old Dec 04, 2001, 11:33 AM
Master
ChrisP's Avatar
Weilbach, Germany
Joined May 2001
2,467 Posts
I wasn't shooting a line with 19 - 20 minutes. My motors have 500+ flights on them, so I guess they're nicely run in rather than run out !
ChrisP is offline Find More Posts by ChrisP
Reply With Quote
Old Dec 05, 2001, 04:13 AM
Registered User
Bill Glover's Avatar
United Kingdom, Bracknell
Joined Nov 2000
11,554 Posts
I believe you Chris, I just can't resist aerobatting my models!

After about 5 mins of tight touch & gos with the geared TS the other week (I was in the circuit with a couple of IC fun-flys and was turning inside them ) I did some aeros and then decided to stretch the flight out by just cruising around. I landed before LVC with just under 15 mins on the timer, when I got home I saw that 3 of the cells in that 2400 pack were venting. Out of interest I cycled it - the capacity came back as 1520 mAh ... definitely gone!
Bill Glover is offline Find More Posts by Bill Glover
Reply With Quote
Old Dec 05, 2001, 09:42 AM
LT
Registered User
Stavern, Norway
Joined Jun 2001
143 Posts
Thanks to everyone who has replied.
You guys are definately getting much more flight time out of your setups than I am. As a matter of interes: What RPM figures should a stock TS have with 7xRC2000 cells?
Bill G:
The batteries was first charged on a Multiplex DUO 3Ampere delta peak charger, after that I gave them an additional slow charge of 200mA for approx 8 hours. The MPX charger has a very sensitive peak detect and will often cut the charging after a few minnutes on empty packs that has been laying unused for an extended periode of time. Discharged by static running on a mabuchi 550 motor. Fast charged a couple of times more before cyckling once on a UI modeltechnics slowcharger/ discharger.
I do not remember the numbers but I would have noticed if numbers <2000 mAh. Specially since the UI uses a low discharge current.
I will do the test again and thereafter charge them with the MPX charger and discharge with UI to compere numbers.
Also, I will measure the current draw.
Larry: Props wrong way around?... Hm.. somtimes I do stupid mistakes so I will dubble check, but not probable.

I am away from home on business right now so my findings will be posted after I get back home in about a week.

Regards
LT is offline Find More Posts by LT
Reply With Quote
Old Dec 05, 2001, 11:08 AM
Official Boat Bum
Eddie P's Avatar
United States, NV, Reno
Joined Mar 2000
7,136 Posts
Also, are you flying just off a fresh charge, or have the packs been charged the night before, then flown? Not to state something otherwise already known by you, but the packs will loose a lot of their charge when sitting around for long periods after topping them off.

Also, you may have advanced the timing of the s400's to a very hot setting. Most people do not time the s400 motor - it is set at a conservative level at the factory that matches a model like the Twinstar. I'll bet you are drawing a lot more amps on those motors than you would at neutral timing. BTW, what connectors are you using? Are they Deans, Astro, or Sermos type? Good plugs also make a difference.

Eddie P is online now Find More Posts by Eddie P
RCG Plus Member
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Flight time on twin EDF50's? KasperE Foamies (Kits) 2 Nov 11, 2003 10:06 PM
F/S Brushless Champion 1hr Flight time on it.Perfectly Built Just charge Batts/fly Lv2Fly Aircraft - Electric - Airplanes (FS/W) 4 Feb 02, 2003 12:12 PM
why such short flight times on my 1020 Kokams nigel99 Batteries and Chargers 9 Dec 20, 2002 02:15 PM
short flight times on a piccolo Ade Micro Helis 6 Dec 11, 2002 11:53 PM
Fourth Flight in on my TWIN STAR KOMET 44 Foamies (Kits) 5 Jun 27, 2001 06:16 AM