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Old Feb 21, 2003, 05:05 AM
Sticky Shepherd
Graham Stabler's Avatar
Oxford/England
Joined May 2001
4,017 Posts
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.

Graham

p.s. I need another car
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Old Feb 22, 2003, 03:21 AM
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billystiltner's Avatar
United States, VA, Clintwood
Joined Nov 2002
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A.
I left my rx standard where left and right drive the rudder and
forward drives the motor.

B.
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.

C.
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.
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Old Feb 22, 2003, 07:52 AM
I don't want to "Switch Now"
pmackenzie's Avatar
Toronto (Don Mills), Canada
Joined Dec 2002
16,711 Posts
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
ZETEX )

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
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Old Feb 23, 2003, 08:14 AM
Sticky Shepherd
Graham Stabler's Avatar
Oxford/England
Joined May 2001
4,017 Posts
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.
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Old Feb 23, 2003, 09:14 AM
I don't want to "Switch Now"
pmackenzie's Avatar
Toronto (Don Mills), Canada
Joined Dec 2002
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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
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Old Sep 21, 2003, 09:28 AM
Oxford Panic
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United Kingdom, Oxford
Joined Feb 2003
3,658 Posts
To use a single coil actuator from the dual coil steering output on a Bitcar conversion see...

http://www.rcgroups.com/forums/showt...ghlight=bridge

Andy.
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Old Dec 10, 2003, 09:58 AM
Nathan Chronister
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Joined Jun 2003
626 Posts
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?
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Old Dec 10, 2003, 10:23 AM
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Chronister

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.
http://www.rcgroups.com/forums/showt...290#post614290

Billy
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Old Feb 03, 2004, 06:40 PM
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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.

Billy
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Old Feb 03, 2004, 07:01 PM
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QLD, Australia
Joined Sep 2003
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Billy,
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 ?
Stewart
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Old Feb 03, 2004, 07:13 PM
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You are right Stewart I'll fix it gosh I posted it in so many places ahhh.

Billy
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Old Feb 03, 2004, 08:08 PM
Registered User
Austria
Joined Jan 2004
10 Posts
Hello,
i have a RX2 with two full Bridges.

A: The general configuration,

Ruder
Elevator
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:

http://free.pages.at/flying/Beardmore.html#Motorregler
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Old Feb 03, 2004, 08:23 PM
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Hopfen you should be able to remove the 100uF cap to reduce weight of rx.
Graham or Gordon you guys can remove the chitchat.

Billy
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Old Feb 03, 2004, 08:32 PM
Registered User
Austria
Joined Jan 2004
10 Posts
yes,
sorry the iron was so hard ;-)

by the older version i've changed him to 33 and had no Problems
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Old Feb 03, 2004, 11:57 PM
Registered User
Los Gatos, CA, USA
Joined Nov 2003
186 Posts
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.

Gerhard
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