Archive for the ‘Modifications’ Category

Transmitter Lipo (3s 11.1v) Stepdown

July 2nd, 2009 4 comments

Rectifer Diode - 1N5404
The convenience of a lipo battery in your transmitter speaks for itself. The problem is many modern transmitters aren’t designed to take the higher voltage that lipos supply. Most transmitters are designed for use with NiCad or NiMh batterys which are 1.45v per cell fully charged, where as lipo batteries are 4.2v per cell fully charged. Stock NiMh TX batteries are 8 cell which equates to 11.6v fully charged by comparison aftermarker TX Lipo batteries are 3 cell which is 12.6v fully charged, that’s a 1.6v difference. Also lipos have a tendency to sit at relatively high voltage for longer unlike NiMh batteries which drop from peak voltage very quickly.

Currently there are plenty of people are using 3 cell TX lipos in there DX7’s and DSX9’s and have had no problems and maybe they never will? I’m guilty of doing this with my DX7 for months now with no problems to date. It’s no secret that the internal circuits of most transmitters is around 3v, which means the TX is using a voltage regulator to stepdown the voltage. Hence the higher the input voltage (from the battery) the more stress you are putting on the TX voltage regulator. So maybe your TX wont go pop immediately but the lifespan of the voltage regulator is probably shortened, either way it doesn’t fill you with confidence.

No one wants to open up their TX’s and mess about with unsoldering and re-soldering PCB components and in the process invalidate the warranty and/or destroy a perfectly functional transmitter. So how about stepping down the lipo battery voltage before it enters the TX…sounds good to me.

The Modification

Diodes have a property call a forward voltage drop, in normal use it’s a side effect rather than something that is specifically capitalized on, however that’s exactly what I’m going to do. By using two 1N5404 rectifier diodes in series (see photo above) on the positive side of the TX battery cable you will effectively have approximately (2 x 0.75v) = 1.5v stepdown. This will bring your lipo down from 12.6 to 11.1 which is a nice healthy voltage for your transmitter and close to what it would expect from a NiMh battery. The 1N5404 is a rectifier diode and designed for power supply/rectification application and is rated for 3A hence it should be fine in this application as the TX is only drawing approximately 300mA (this varies from TX to TX, normally it’s stated in the manual).

TX Stepdown Mod

One thing to note is the diode stepdown can not be part of your charging circuit otherwise your lipo charger will complain about the voltage or in the worst case you might have a “little” fire on your hands :( The battery I used was a Outrage XPTX 11.1v 2500mAh (see photo) which has a TX plug, a standard rc connector and a balancer plug (Thunder Power) all pre-wired which turns out to be very handy.

Below you can see the redundant rc connector which is used to charge the lipo hence isolating the stepdown.

TX Stepdown Mod Installed

I urge anyone who is considering attempting this to do there own research in order to better understand what they are getting into. Here are a couple of links that may help:


Don’t know yet too early to tell…seems fine so far 😛

Review: MicroHeli Trex 700 MOD 1.0 Gear Conversion

June 28th, 2009 No comments

The ultimate main gear upgrade to strength the Trex 700 drive train.

Trex 700 Main Gear Mesh Continued…

June 23rd, 2009 No comments

When I first built the Trex 700 one of the many issues I found was the main gear moves several mm up and down (in addition to all the meshing issues).
I simply put it down to poor manufacturing tolerance and accepted it, but as it turns out this movement up and down is due to poor assembly of the “main oneway bearing assembly”.

After seeing several gears strip at the field in the weekend, this up and down main gear play was debated and someone (Peter – EMHC) explained how they removed it.

This is just another weak link in the chain that is the Trex700 drive train, which can be completely corrected, this is how.

Bearing Alignment Before Adjustment (NOT flush with the top of bearing housing)

Mainbearing Trex 700 - Before

Bearing Alignment After Adjustment (now flush with top of the bearing housing)
Mainbearing Trex 700 - After
Steps to correct bearing alignment:

  1. Take the main gear out and remove the auto-rotation gear
  2. Remove the one-way sleeve, unscrew the oneway bearing housing, now remove the one-way sprag bearing
  3. Get a 15mm or similar socket (from a socket set) and a hammer, use the socket and hammer to reposition the bearing flush with the top of the oneway bearing housing.
  4. Re-shim the main shaft at the collar if required.
  5. Done

Trex 700 Gear Mesh Mod

June 11th, 2009 No comments

Gear mesh on the 700 is very important as the main gear has a 0.7 mod (fine gear mesh normally found on 50 size heli’s). In order to mesh the gears correctly you need to adjust the main gear to pinon gear gap and also auto rotation gear to tail gear gap. This can be achieved by grinding down the nubs on the clutch block and plastic tail case (see photos). In addition you will need to replace the screws with standard non-specialty button head screws and use the specialty washers from the Trex 600. This will need to be done for clutch block, plastic tail case and engine blocks. This will give you enough play to adjust the mesh.

Upgraded Metal Clutch Block with Grounded Metal Nubs

Trex700 Clutch Block Mod

Tail Case with Ground Plastic Nubs
Trex700 Tail Case Mod

Lipo Glow Igniter Mod

June 10th, 2009 No comments

What do do with your old Align 2n1 Regulator
…because if the controller ribon breaks the regulator fails off

This creation gives you a glow igniter which is fast to charge, has an auto off, battery status, indicates a when glow power is being supplied and when the circuit is connected. Also it has a standard RC connector for a regulated 6v power supply. In my case it’s handy for powering the bluetooth adapter for my Spartan DS760 gyro, but it could really be used for anything, especially during setup.

1xPlastic box (old Align box)
1xAlign 2n1 Regulator
1xGlow extension
1×7.2v2S lipo

Lipo Glow Igniter