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Old May 31, 2004, 04:56 PM
Stuck on a rock
epilot's Avatar
Germany, NDS, WOB
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Rave
Bit ESC (BitSC)

Thanks to Dave Burley I am now have a throttle for my Bit planes. Dave wrote the code and programmed a PIC that will read the outputs from the Bit RX and gradually increase/decrease the "juice" that flows to the motor. The ESC consists of only 3 parts: A MOSFET (IRLML2502 is suitable), a 20K resistor and the PIC microprocessor. I just hooked up the ESC to a Bit RX as shown in the pictures; wires go to V+ and ground and 2 outputs (I used the forward/reverse outputs for the test). It works beautifully! Hold down the "forward" key and the motor RPMs increase. Pressing "reverse" reduces RPM. Once a key is release the setting is held. I find that it is easiest to adjust the throttle setting by simply pulsing the appropriate key. The throttle has 32 steps so the resolution is good. By having a throttle you will have much more control over your model. Obviously rudder is still a bang-bang system but by pulsing the "turn" keys you can make wide circles. I have flown several rudder/throttle models in the past and if the model is properly trimmed you do not really need elevator control. Remember that altitude in real aircraft is controlled with the throttle. Before you start asking for more details let me add that Dave will jump in and supply more info about HEX files for the PIC and maybe offer some parts support. All credit for the "BitSC" goes to Dave; I'm just the "crash test dummy" who goaded him into making the ESC for me since I am too dumb to do it myself

Michael
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Old May 31, 2004, 05:17 PM
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United States, VA, Clintwood
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Michale
That is cool. I had wanted to make something like that but never persued it. Glad you did. Can't wait for the Hex file. Thanks a bunch. There is a similar mod in the RX mod thread but uses more parts I think. The PIC will be simple to add.
Not much more work than adding a fet.


Billy
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Old May 31, 2004, 05:25 PM
Stuck on a rock
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Billy, read the text again. All thanks need to go to Dave Burley.

Michael
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Old May 31, 2004, 05:33 PM
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Thanks Dave Burley for programming the PIC and making the circuit.
Thanks Michael for getting him to do it. You have to give yourself a bit of credit for goading and being the "crash test dummy".

Billy
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Old Jun 01, 2004, 12:46 AM
Team30 Micro EDF
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Bring on the schematic!

wheres the R20k hiding in the photo?
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Old Jun 01, 2004, 01:41 AM
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Portland, Oregon, USA
Joined Nov 2003
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Michael,

You sure put that together quickly upon your return from vacation. Glad you
like it. The design is like one I did about 4 yrs ago but much simpler this time.
Glad you "goaded:" me into it. I've got bit cars laying around but been stuck
in electronics land forever, with no time to for buliding. Within a few days I'll
post the source and hex files for this design along with a schematic. In the
meanwhile here is a photo of the "hidden" 20K resistor ready to be soldered
between the legs of the mosfet.

Dave
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Old Jun 01, 2004, 03:41 AM
What goes up must come down..
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Many thanks Dave! jezz that thing is small! I would say that the max amp would be the same as what the IRML2502 can support right? By doing so does it mean that the output transistor mod is no longer required on the RX? I have to read more about those PIC..but I am a bit late..+ I don't have equipment to do so, but its fantastic, I remember Vilas had one done by someone (maybe it was you Dave?) but never came back to me with info's about it. Now Dave do you think it's possible to "pulse" the rudder? even if its not proportionnal, I beleive it would help...
Roger B.
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Old Jun 01, 2004, 03:57 AM
Stuck on a rock
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Roger, the IRLML2502 is fine up to app. 1amp continuous. You do not need to do the mod on the receiver itself - the motor power is passed by the BitSC MOSFET.

Once you have developed the knack of pulsing the rudder (takes app. 30 seconds to learn) you will wonder why you worried about proportional. I can fly large, precise figure-8s this way.

Michael
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Old Jun 01, 2004, 04:19 AM
What goes up must come down..
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Micheal,
always the same that get lucky! (you well deserve it) LOL, it sound nice then with an ESC no more RX mod is required...
I have to search about this thread where the fellow modeler was posting about full bitcharg TX mod that goes as a "full propo" on both channels...using MAX 923 and 922 IC chips BUT he swap some parts from a Futaba radio. I tried but never succeed..
Roger B.
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Last edited by rodair; Jun 01, 2004 at 04:28 AM. Reason: typo
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Old Jun 02, 2004, 04:39 AM
Sticky Shepherd
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very cool
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Old Jun 02, 2004, 05:26 AM
always too heavy
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Austria/Europe
Joined Nov 2003
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Michael,

very good solution. Where did you buy or which brand is the board with the SMD version of the RX2 chip?

I think making the bitchar propo by pulsing the transmitter is very hard to do because of the type of coding of the functions. Function "left" needs 8 millisecounds of start-code followed by 58 millisecounds of function code, function "right" needs 8 millisecounds of start-code followed by 64 millisecounds of function code. So pulse rate at propo pulsing can only be very low.

Herbert
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Old Jun 02, 2004, 06:10 AM
Stuck on a rock
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Hi Herbert

The RX is from one of the "Stunt" vehicles (the ones where the front wheels spin). The RX chip is not a RX2 but has SM6135 written on it and is a clone of the RX2.

I am aware that what can be acheived by pulsing is limited but it does give you the ability to make nice big turns and still have rudder power for tight turns.

Michael
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Old Jun 02, 2004, 06:29 AM
What goes up must come down..
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Micheal,
any mod on the RX "Stunt" car? on the TX?
Did you use it with N20 /U80with it? How happy about this one so far? any comments..
I saw some finally over here yesterday, your comments here would be appreciated and oh yes, what freq do you use now?
Thanks for your time,
Roger B.
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Old Jun 02, 2004, 06:39 AM
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Hi Roger

I have not modified the TX yet but it will get the voltage regualtor mod and a longer antenna. Only mod on the RX is a longer antenna. Since the stunt car RX has 2 bidirectional outputs there is no need to switch the TX controls. The mosfet will be fine with N20/U-80 combo since the amp draw is app. 800mah. This set is on 40MHz.

Michael
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Old Jun 02, 2004, 06:48 AM
What goes up must come down..
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Micheal,
That was fast!, thank you!
I will then by one even if the LHS is asking too much ~ $10 US for it (twice what it worth and more) , I would have it right away..
Roger B.
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