Help me Mod Futaba MCR-4a to Rx only

[dtknowles]

I have 3 Futaba MCR-4a AM Rx / ESC /BEC units. On two of them the speed control function is not working. The speed control on these units is old frame rate technology and not worth repairing. Since I have two matching Tx and I have never had problems with the Rx function, I would like to get more use out of these units. I would like to convert at least one to a 4 channel Rx only. Disable (and possibily remove) the speed control and BEC and bring out the throttle channel to be connected to a modern speed control.

Tim Knowles

[JMP_blackfoot]

Tim, I think I have one in the basement. Time permitting, I'll have a look at it this week-end to check whether the modification is simple, and keep you updated.

[Mr.RC-CAM]

I suspect the Rx has a standard shift register decoder. It will be easy to solder a servo wire to it. Just check the IC's on the board. Do you see a CD4015 16-pin IC on it? If so, the throttle (Ch-3) R/C signal is on pin 3.

RC-CAM

[dtknowles]

It has a 24 pin IC TR3T16A Futaba Japan S 8952 B . The pins are really fine. There is a pot on the board that adjusts the throttle end point/span. Picking up one of its solder pads would be a lot easier.

[dtknowles]

Thanks guys for trying to help out. I meant to thank you is the last message :o

[Mr.RC-CAM]

I'm not sure what a TR3T16A is, but at 24 pins it must be an AM demodulator IC. Are you sure there isn't another IC in there? Check the other side of the board too.

If this part is the decoder, then your ohmmeter will show continuity between the three servo channels and the respective pins on the IC.

RC-CAM

[JMP_blackfoot]

The throttle channel (channel #3) is available on the two rectangular pads in the center of the picture. They are connected to the corner pin and the third pin.
The fourth pin is channel #4. Channels #1 and #2 are on the first two pins of the other side of the chip.
The chip on the right hand side of the picture is the BEC voltage regulator, which I think could be removed, as could the three standing transistors and the big diode.
For RC-CAM's data base, I have added pictures of both sides of the receiver, whose RF and IF does not use any IC, and the receiver in its case, arming switch and all...

Good luck.

[Mr.RC-CAM]

Thanks for the photos. That is definately a vintage RF design. If you find any data on the IC it would be interesting to see the details to it. I suspect it is a microprocessor.

RC-CAM

[JMP_blackfoot]

It is in fact AM, and the date code on Tim's reads :TR3T16A Futaba Japan S 8952 B, which tells that the chip was made in the 52nd week of 1989. Mine reads : 9044, meaning the 44th week of 1990. I bought it in Japan in 1991 or 1992.
As for the chip, I could identify no resonator or crystal near it, so I'm inclined to think along the lines of a PLA (Programmable Logic Array).
Otherwise, the receiver part works quite well indeed.

[bigandy]

It might be an ASIC (application specific IC) with all the RF and decoding stuff on board. If Futaba used them in failry high volumes, then I would put money on it being that...

Cheers
Andy

[JMP_blackfoot]

The RF and IF part are all discrete transistors, as can clearly be seen on the photos.

[dtknowles]

The throttle channel (channel #3) is available on the two rectangular pads in the center of the picture. They are connected to the corner pin and the third pin.
The fourth pin is channel #4. Channels #1 and #2 are on the first two pins of the other side of the chip.
The chip on the right hand side of the picture is the BEC voltage regulator, which I think could be removed, as could the three standing transistors and the big diode.
For RC-CAM's data base, I have added pictures of both sides of the receiver, whose RF and IF does not use any IC, and the receiver in its case, arming switch and all...

Good luck.

Thanks again JMP. Just the kind of help I needed. I was think to pull the FET's, the voltage reg., the diode and the two big caps off the board and solder a servo lead in for the throttle/ESC connection. I think that my skills are good enough to hit the solder pads you indicate in the photo. I would like to do this soon but tomorrow is flying day, normally not much time for other stuff. I guess I will leave the caps for now. I think that first I will pull the other items, connect a servo to the channel 1 pins and a battery to the pos and neg pins on another channel and see if I still have an Rx. I guess that I can pull all the wires except the ant. as the on/off switch is between the motor/battery pos. and the voltage reg. Do you have a microscope to take those pictures? When I get the big stuff off the board maybe I can see if the arming switch leads will ned a jumper.

Tim

[dtknowles]

:D It really works, I just got up from the computer and did it. Throttle stick moved a servo :) Now I have another Rx so I will not have to swap as much. And I have another that will get the same treatment.

Thanks

Tim

P.S. What might that little board be next to the MCR-4a in the last pic?

Here is a picture of the modified Rx
http://members.aol.com/dtknowles/modifiedmcr4a

[JMP_blackfoot]

:D It really works, I just got up from the computer and did it. Throttle stick moved a servo :) Now I have another Rx so I will not have to swap as much. And I have another that will get the same treatment.

Good, congratulations and happy flying!
Nothing works like team work! ;)

P.S. What might that little board be next to the MCR-4a in the last pic?

It's a 3 channel receiver I produce for magnetic actuators, with on-board ESc for small models. It weighs 2.5 gram complete. More details here :
http://www.bsdmicrorc.com/products.cfm?catID=10002
I also make a 4-channel one for 3 servos, also with on-board ESC, of similar weight. That's about 1/20th the weight of the MCR4A for the same functions.... :) (1.5A only, though)

I use a Sony DSC-S70 still camera of several years vintage, which allows for macro picture taking, as close as 40 mm.

[dtknowles]

Thanks again, JMP. I wish someone else had done the leg work here to find an indoor flying site so I would have a use for your little Rx's. Winters are so short here that not much push for indoor flying.

[dtknowles]

Some one else has asked for help on this mod so I am posting a labeled picture.

[don_craig]

Thank you thank you thank you, Tim! I'll try to make some progress with this....

dc

[dtknowles]

Thank you thank you thank you, Tim! I'll try to make some progress with this....

dc

Don't rush, do it when you are ready. I should have mentioned that all the wires go away except the antenna.

Tim

[don_craig]

Do you have a slightly closer-up shot of the modified Rx (esp. so I can see where the servo leads go on to)?

Thanks again!

[dtknowles]

Do you have a slightly closer-up shot of the modified Rx (esp. so I can see where the servo leads go on to)?

Thanks again!

I am putting a picture here and there is a close up of the throttle servo signal lead location earlier in this thread maybe the fifth post or so. I guess you know where to go to grab the pos and neg for the servo.

[ncpiperpilot]

Wow found this post, while not exactly the info I wanted seems like a good place to ask...

I have a couple of these Rx/ESC combos and was thinking about modifying them so I could use a LiPo.

1. I would love to find a schematic, anyone have one?
2. What is the designed LVC of this unit? Hard to believe but it's not in the Specs.
3. Does anyone know whether the voltage detection circuit is inside the IC or whether there is just a pin on the IC to activate that will cause it to go into LVC? if so...Which pin?
4. ...or maybe there is discrete circuitry that does the detection and shutdown without "help" of the IC. Anyone know?
5. Also, anyone know what the Gate drive circuit for the FETs looks like? Is there a resistor in series with the Gate drive?

At any rate, assuming I find enough time to play around with it, (and anyone else is interested) I would be willing to post a circuit that we can use to change the LVC for LiPos.

Yeah...I know this is old technology....but it's really a pretty good radio for a electric sailplane. I am sure the old mothballed Gentle Lady would fly a lot better with a 2S 7.4V LiPo than it did with the 1400mAH NiCd pack.

...Bill

[JRuggiero]

ncpiperpilot,

IIRC, there was no LVC. I flew this radio more than ten years ago using 6 and 7-cell NiCad packs. I sometimes ran the batteries down so far that there was no capacity left to run the servos. Shutting off the motor re-enabled the servos, so I could land the airplane. So I suspect that if you were to run Li-Pos (no more than 2S; I don't think the MCR-4A could handle 3S) you would have to monitor your running time and land while the pack still has a lot of capacity left.

The receiver was a single-conversion design, but it had plenty of range to operate in my motor glider at considerable distance. I don't recall having any problems with glitches.

Jim R