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Other › Can't get going properly!
12-04-2005 04:09 PM  12 years agoPost 1
jurgen

rrApprentice

Weybridge, Surrey, UK

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Help please!!

Ok, first the setup:
1. T-Rex 450XL with a custom e-ccpm mod.
2. 3 X Hitec HS-56's on cyclic.
3. GY401 and HDS-877 digi on the tail.
4. 2 X RC expert 1800 Li-Po's and a brand new FP Extreme - Kapton 3s1p 2200.
5. Futaba R149DP RX and FF9 TX.
6. SAB carbon blades.
7. Align 25A ESC (non-governor version).
8. Align 420LF outrunner motor with an 11t pinion.

Now the problem:
I am new to electrics (but with experience with a Raptor 30) and so the learning curve with the batteries/motor/speed controller/etc is steep!

I started out just using the stock Align Rex with the RC Expert batteries and servos (straight off E-Bay) and I planned to upgrade as I saw fit. I started on the 13t pinion (just because I didn't know what else to start with so I went for the middle option!). Everything was running smoothly and I was enjoying the Rex and started experimenting with some mild aerobatics. I went inverted and was holding a hover, decided to flip out and the motor died! Damn! Plonked it straight into the ground on it's tail...

Anyway came off pretty lightly and decided now was the time to do some of those upgrades I was planning on. So hence the new battery (as I no longer trusted the RC Expert ones!) from FP. I got the Hitec servos and the digital for the tail. I got carbon blades and modified the e-ccpm arrangement to suite the Hitecs and to have them mounted directly under the swash. I bought a dedicated LiPo charger to make sure I was getting a good charge and also a "Stay Balance" module from Flight Power. Oh, and I installed a little LiPo guard (which is nothing more than an LED which comes on if the battery voltage goes below 9V).

So after all this today was the day to go and test fly the new setup and mod. (I also put the 11t pinion on as I thought it would draw less current from the motor?) I lifted off to a gentle hover with one of the RC Expert batteries and trimmed the servos out (glad to see my e-ccpm mod worked!) and started setting the throttle curves. And then the little LED came on! SO I thought "OK, so these RC Expert batteries aren't great". I landed, swapped the batteries (for my second RC Expert pack) and took off for some more trimming. The LED came on almost instantly! I thought "OK, that ones really poked."

So now I put the brand new FP pack in and took off. Exactly the same! The LED came on straight away! That's my problem, why is the voltage dropping to 9V so quickly? (Just to clarify the LiPo guard is connected in parralel to the ESC's input, so straight off the battery).

A few questions:

1. Why am I experiencing this problem? Is it the Align ESC and motor? Do I need to go CC and hacker route or something?

2. Was my reasoning about the pinion correct? i.e. will a lower toothed pinion (like the 11t) draw less current than the 15t one because the motor is geared lower? Or is the current related to the RPM of the motor and so by using the 11t I'm actually drawing more current because of higher RPM to maintain the headspeed?

3. My throttle curve on the FF9 is something like 100-85-70-85-100 in IDLE UP1, does that seem reasonable?

4. Just generally any tips that will help me on the way to happy Rexxie flying!

Thanks guys and apologies for the long post, just trying to make sure I get as much detail accross as possible!

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12-04-2005 09:28 PM  12 years agoPost 2
Ken Filloon

rrVeteran

Highland, Michigan

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12-04-2005 09:43 PM  12 years agoPost 3
steph

rrKey Veteran

Hampshire England

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Hi jurgen_r30

Your questions are very reasonable ones and its a nightmare to get started in this electric hobby as there are so many variables i see you live very close to where i am if you need assistance first hand i can help give me a pm we can possibly get together and sort out your problems

The world is round you can run but you will always end up where you started from

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12-04-2005 09:59 PM  12 years agoPost 4
Mr_Nils

rrNovice

Kristiansand, Norway

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Are your LiPo guard for 3 or 4 cell? (9V or 12V)

Nils

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12-05-2005 07:46 AM  12 years agoPost 5
jurgen

rrApprentice

Weybridge, Surrey, UK

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The LiPo guard is for 3 cell.

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12-06-2005 09:00 AM  12 years agoPost 6
jurgen

rrApprentice

Weybridge, Surrey, UK

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Ok, so I did some tests and basically I've discovered that the LiPo guard was the culprit!!

I measured the voltage on the battery pack while the heli was on the ground and spooled up (dangerous, I know!) and it was reading a healthy 10.5V and yet the LiPo guard was glowing red!

I removed the heatshrink and luckily it is a really simple circuit and uses a resistor voltage divider to get the reference voltage so I'll be able to tweak that.

Thanks for the help guys.

P.S. I'll probably post the circuit diagram later for those interested.

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