web development & design: mike manning                                                                             

 

 
WHY USE
  

In the 1/8 final at the last round of the summer series I found that after about 2 thirds of the Final my car would 'lose radio' just as I braked hard for the top bend. My driving style with my 1/8 means that I brake very late just before the corner and then start to turn as I release the brake. I was finding that with the brake hard on the steering just...well DIDN'T!
As I did more laps this got worse. The radio just seemed to blank out. It did nothing wild, just appeared to stop.
A similar thing happened to me on my 1/10 but I just put it down to interference.

I had been looking into the Li-Po thing several months now and knew that Serpent had been testing Li-Pos in Europe and the US for a little while so I decided to experiment.

I looked around to find a trade supplier of the cells that I wanted (KOKAM..the original and very much the BEST) together with a top quality voltage dropping circuit that was not about to take up all the room on the radio tray. I eventually contacted Mike at Aurorra who was very interested in my project and was happy to supply the components for me to make up a kit.

I fitted Futaba type plugs & sockets to all the leads and then fitted the complete package to my car (see pics below).
After much testing (several drivers are now using these kits) I have found the system to be (so far) absolutely faultless. The 1st pack that I used was 640mah (I now supply 910mah) but even this gives about 45minutes (9 tanks?) of use and even then the pack was still around 35% full. NO glitches or loss of power and....the radio appears to be much quicker..(see Note 2 below).
This is easily explained though each cell (2 x cells per pack) are 3.7 volts (=7.4 volts) and the Inverter brings this down to a VERY constant 6 volt supply that radios require. Therefore there is no slow drop off in power to the radio/servos, resulting in more speed & torque.

I have now fitted my kit to my 1/8 car (but with the new 910mah pack) and have had very positive results with this. No more dropping out of servo power.
I have also now fitted a Li-Po to my transmitter and, although I cannot see any actual performance improvement, the radio stays charged for weeks as opposed to days...Wicked!

There is a downside to using Li-Pos though and this is that you MUST use a proper charger designed for Li-Pos ONLY. Mike at Aurorra has done extensive testing of many chargers and found several to be, well downright poor! Beware the chargers that profess to charge ALL types of cells...generally they are NOT to be trusted with Li-pos!

If you need any more info regarding Li-Po set ups for your car then don't hesitate to contact me on 07966-415712 or mail me on mike@mmmrc.org and I will be more than happy to assist.

Mike M

CLICK ON PICTURES TO ENLARGE

CLICK FOR BIG PICTURE
This picture shows the Li-Po pack fitted to the 'very simply' modified battery tray of a Serpent 710/720 but fitting to any other car (Mugen, Team Magic etc) is just as easy!
The 'Charge Lead' in the pic is for 'balance' charging. If you don't have a charger/balancer then use the Power Lead.
CLICK FOR BIG PICTURE
Here you can see the slimness of the Li-Po pack (the tank on this 720 has been lowered). Leaving the pack in place it is possible to fit the 6 volt invertor on top of the pack. This looks more neat but I would recommend that it is fitted on the radio tray.
CLICK FOR BIG PICTURE
The 6 volt Invertor (the blue pack shown here) is a VERY important part of the kit. The Li-Po pack is 7.4 volts and needs to be ACCURATELY controlled at 6 volts to match most radios. Most 'regulators' produce various forms of radio interference and can cause havoc with a radio receiver. This is why it is so important to select a high grade module.
CLICK FOR BIG PICTURE
Another view of my completed Pi-Po radio tray set-up. I use a 'Y' lead from receiver to the radio tray, with the double socket end fitted to the radio tray with either 'Fender Mender' or Super Glue. This allows for easy connection of both Personal Transponder and the power lead from the pack...In this case via the '6 volt Stabiliser.
 
If you have any questions regarding the use of Li-Po Cells in your cars then please don't hesitate to e-mail me or see me at the Club.
Mike M

Footnote 1:
This loss of receiver signal strength has proved more problematic recently, especially when using Digital servos, with the new type 2.4gig Radio systems (Spektrum etc).
Footnote 2:
I have heard rumours that people consider that Spektrum radio is 'slow'. Having tested this extensively for nearly a year I now realise that this is because the Spektrum DOES NOT like voltage drops (being digital) and just loses performance.
Mark Green told me that he acrtually turned down the speed on his steering after he fitted his li-po pack!

Footnote 3: Dez Chand (Radio Race Car) has now done exrtensive testing on the 2 amp Invertors that we use and found them to be more than enough amperage with a heavy racing truck with huge wheels over a rough racing surface at race distance..
It 'MAY???' be neccesary to use a higher amperage (5 amp)invertor on some multi-servoed' large scale cars though.
Mike M.


 
WHY USE LITHIUM POLYMER Part II?
  

The arrival of lithium polymer technology in this last two years has provided the ability to achieve power performance better than Nitro powered cars.

This same technology can also be applied to the powering of the receiver and servos in Nitro powered cars.

The immediate advantage of Lithium polymer technology is the power to weight ratio. A fully charged Lithium polymer cell is 4.2V as opposed to a Nicad or Nimh at about 1.2V. A lithium cell capable of delivering over 8amps continuously weighs only 18gms!

A suitable 2 cell lithium polymer packs weighs only 36 grams and has a fully charged voltage of 8.4V. Use of a high grade inverter type BEC can step this voltage down to a steady fixed 6Volts even as the battery discharges down.

The following are the major advantages over a standard receiver pack:

1… Weight reduction

2….A highly regulated constant 6V output from the BEC irrespective of the loading from the servos.

3… Servo speed assured at all times

4… Receiver signal strength is assured at all times because the receiver voltage is not pulled down (this effect causes loss of range during heavy servo loads).

(My sincerest thanks to Mike Redmond of Aurorra Ltd for the above article.)

 

 

 

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