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Feb 21, 2003, 06:05 AM
Sticky Shepherd
Graham Stabler's Avatar
Thread OP

Bitcharger receiver mods

This is the third in the series of Bitcharger stickys. For links to the others check out useful threads, thread.

Can people please post concise details about their receiver mods.

We need to know about

A: The general configuration, e.g. using the motor connections to drive the actuator and the rudder to drive a mosfet.

B: Any modifications to the board itself e.g. adding mosfets for the throttle.

C: The choice of actuator, bifilar, two coil or traditional one coil.

D: Advanced mods.

If you proceed any descriptions with the corresponding letter then it wil make it easy to brouse.

If there is anything I have missed I'll add a letter.


p.s. I need another car
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Feb 22, 2003, 04:21 AM
Registered User
billystiltner's Avatar
I left my rx standard where left and right drive the rudder and
forward drives the motor.

I added an N-channel mosfet for throttle.
Basic wiring instructions for standard rx2 chip
1) Find a leg on the rx chip that goes high when you press forward on TX
2)cut the trace that leads to this leg
3)connect gate of fet to this leg
4)connect gnd to src of fet
5)connect drain of fet to motor
6)connect V+ to other wire on motor

hanging garden style fet mounting

Note: in schematic the circle with b represents the rx2 chip but was drawn to actually represent cob blob on motorworks rx.
Instead of cutting traces 2 transistors will probably have to be removed on the motorworks rx.

Since my rx came with 2 coil steering I had to wind 2 coils (bifolar or bifalor or bifiler how do you spell it?)into 1
procedure as follows.
Take 2 lengths of wire and wind them at the same time onto a straw about 4-5mm wide. Add glue as you wind.
White glue(elmers) works fine and use duco to mount
then you can remove with acetone without messing up the coil.
Mine ended up at 56 ohms apeice @ ~ 150 turns.
Connect the start of 1 coil to the end the other coil this goes to V+
and the other two wires go to l and r respectively.
Placement on rudder is normal BIRD style with magnet.

Thanks to Grahm for explaining to me how to wind and connect the bifilar coil.

Oh PS wrap plumbers tape or saran wrap on the straw before you wind so you can pull the coil off the straw.

If anyone can explain this in a less confusing manner it would be good.
Last edited by billystiltner; Feb 22, 2003 at 04:53 AM.
Feb 22, 2003, 08:52 AM
I don't want to "Switch Now"
pmackenzie's Avatar
A: since mine was a two coil car, I exchanged the motor and steering. This enables the use of a
single coil, if desired.

B: Replaced the R and L transistors with ZETEX ZXMN2A01FTA fets. Like the IRLM2502 these
can be soldered to the board in place of the original parts. (The IRLM2502 would be better than the

C: I used the two coils that came with the car, wired in series. The magnet is mounted to the rudder, and one coil is on each side.

D: Two speed motor, by connecting the motor as shown below. In my case the value is 2.35 ohms
Feb 23, 2003, 09:14 AM
Sticky Shepherd
Graham Stabler's Avatar
Thread OP
Excellent so far!!!! As I had the pic already I have knocked up a version of the above diagram showing the board itself. Remember that you probably don't want the smallest resiter ever, it has to absorb power P = I^2 X R so once you have an idea of the current work out the rating of resister you need.
Feb 23, 2003, 10:14 AM
I don't want to "Switch Now"
pmackenzie's Avatar
Your version of the schematic makes everything quite clear. I will only add that the external connections are easier to make on the opposite (back) side of the board.
Pat MacKenzie
Sep 21, 2003, 09:28 AM
Oxford Panic
AndyOne's Avatar
To use a single coil actuator from the dual coil steering output on a Bitcar conversion see...

Dec 10, 2003, 10:58 AM
Nathan Chronister
Chronister's Avatar
Hello. I read online that "If your power source is between 2.5V and 5.0V then you can remove the DC-DC components (driver transistor/controller, inductor, input electrolytic cap) to save weight. " Does anyone have details on how to perform this modification? And is it possible to simply remove the large capacitor without doing anything else?
Dec 10, 2003, 11:23 AM
Registered User
billystiltner's Avatar

The way to remove the DC-DC components is in the big thread.I forget which post but it is on one of the first few pages I think.
The post is by Graham showing a diagram. Some folks have had trouble with this mod. I have replaced the 100uf cpacitor with a 10uf cpacitor and experienced glitching. I have also removed the DC-DC converter components and bridged the appropriate traces.
I had reduced range about 100-150 ft instead of 180ft but no glitches untill I shortened my antennae. The antennae length that worked without glitching was twice the lrngth of a stock car antennae. It could also be that shotening the antennae had nothing to do with my rx glitching, it could be possible that now the RX2 chip has been damaged. I have not yet change the antennae length back to find out but will soon. So unless you have a lot of RXs to experiment on I would wait to do the DC-DC removal.

Here is a link to a photo and drawing showing the DC-DC removal.

Last edited by billystiltner; Dec 10, 2003 at 11:33 AM.
Feb 03, 2004, 07:40 PM
Registered User
billystiltner's Avatar
I have been able to remove the DC-DC components with accepted range for a very tiny model airplane. I do not recomend trying this! But the info is posted for those that wish too. It does work for me but it may not work for you. It has been suggsted by others not to do it. The modification will decrease your range. So it is not improving the performance of th RX in any way. The only reason I have done the modification is so that my small airplane will fly a little bit slower. You must start out with a car that has good range to begin with. The motor will have to have a very little current draw as well as the actuators. This mod will probably not work at all with stock coils. It will probably definately not work with echarger and N20 motors. My coil is 80 ohms and the motor draws about 280ma at 3.5V. The length of the antennae and all connecting wires is critical. Keep the motor ,battery,and actuator wires as short as possible. The RX antennae on my rx with DC-DC removal is 14cm. It is a 49MHz rx.
I also have done the Voltage regulator modification on my TX. The DC-DC removal did glitch at certain angles till I added a 3.5 foot antennae to my TX. Now with the DC-D removal , longer TX antennae, perfectly adjusted RX wire lengths the range is only
about 80ft at eye level. I think the car had this much range to begin with. The range is more in the air though.

I flew my 10" mite in a gym the other day.
It had the rx with Dc-dc removed completely
and the range was enough to fly from one end of the gym to the other with no interruptions in signal. I did have a new 9V in my TX so the previous glitching could have been due to a low battery.

Last edited by billystiltner; Mar 05, 2004 at 07:11 PM.
Feb 03, 2004, 08:01 PM
Registered User
I think you must mean CM not mm on your antenna 14mm is just over 1/2" 14 cm is just over 5 1/2 " , am I correct ?
Feb 03, 2004, 08:13 PM
Registered User
billystiltner's Avatar
You are right Stewart I'll fix it gosh I posted it in so many places ahhh.

Feb 03, 2004, 09:08 PM
Registered User
i have a RX2 with two full Bridges.

A: The general configuration,

Speed controll + -

B: Any modifications to the board

1 MOSFET see "D"
no dc Converter
100 Ohm -> 1 Kohm (4x)

C: The choice of actuator
two single coils (Ruder and elavator)

D: Advanced mods.

changeable speed + -
i have used the turbo conector.

a short push Turbo give more speed
Elevator down reduce speed, sorry, but i think its the best way for 5 chanel.
-> Elevator down must not bee big!

Time for max speed change up/ down is about 3 sek

it consists of 5 SMD incl. FET in analog design (Miller integrator)

see Description, sorry only in german:
Last edited by hopfen; Feb 03, 2004 at 09:13 PM.
Feb 03, 2004, 09:23 PM
Registered User
billystiltner's Avatar
Hopfen you should be able to remove the 100uF cap to reduce weight of rx.
Graham or Gordon you guys can remove the chitchat.

Feb 03, 2004, 09:32 PM
Registered User
sorry the iron was so hard ;-)

by the older version i've changed him to 33 and had no Problems
Feb 04, 2004, 12:57 AM
Registered User
Hallo Hopfen,

I think your modification is very interesting, and I would like to try it.
I went to your site, but I could not find the schematics of your modification, nor could I figure out what the "turbo" connection is, for either the transmitter or the receiver. Is this a special version of the transmitter and/or receiver? - If not, how do you add the turbo function to the transmitter?

I do have some receivers that have the RX-2 chip as an SOIC, so I can get to all the pins.

Thanks in advance for your help.


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