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M51660L and L298D Pin Connections for DIY RC Servo/Motor Board...?

Hello Everyone,

As of today, I am a brand new member of this forum, although I have been quietly reading and learning all the great info available from the sidelines for a while now.
I'm a complete newbie when it comes to robotics and solid state circuitry... but I've been building thermionic valve/tube audio stuff for years, so I know how to solder up a board!
I guess I have reached the stage in my project where I've become a bit stuck...(it had to happen at some point!)...and now need some help from the more experienced electronics people frequenting this informative forum.

A quick overview of my project....it's a proportional (RC Spectrum Tx/Rx interface) rotating mechanical arm (360 deg +), driven by a home-built servo-motor, which comprises of a medium-sized 6 volt dc gearhead motor, driven by, again, a home-built motor control board with potentiometer derived positional feedback...just like a big version of yer standard rc servo really.
I'm about to begin construction of this motor/servo driver board...and herein lies my problem.
I'm going to use two ic's for this custom board, the Mitsubishi M51660L RC Servo Control/Driver,
and an SGS Thomson L298D Dual H-Bridge Driver.

I'd like to use the L298D to augment the motor current capabilities of the board, because the M51660L's own built-in H-bridge (and it's two external pnp transistors) only have the capability for 100mA or so, and would burn up pretty quick if I tried to drive my somewhat larger gearhead motor with it's designed loads, from the M51660L circuit alone.
I intend also, to use the L298D in parallel mode, doubling it's normal 2A dual channel inputs/outputs into a single, well heat-sinked, 4A motor driver.This should give me plenty of 'worry-free' headroom from overheating the circuit with this particular gearhead motor.

Now this is the bit where I find myself stuck...can some kind soul here tell me how to go about connecting the output pins of the M51660L and the inputs of the L298D to each other to achieve this?.
I know how to wire the pins on the L298D to get parallel mode, but I'm not sure which pins on the M51660L,
(pins 6 + 10 - Outputs 1 + 2, or pins 4 + 12 - ext. pnp transistor drives, or all four of them...??) to connect to the inputs (pins 5 + 7), Enable A and Enable B (pins 6 + 11) on the L298D?.

Also, my supply voltage to Vs (pin 4) on the L298D will vary between 6 volts and 7.5 volts in use, can I use this point to take the supply for L298D's Vss (pin 9) logic supply too, and maybe also the Vcc supply (pin 14) on the M51660L..?? or will I have to regulate that particular supply seperately down to 5 volts via a BEC circuit via the Spectrum Rx?.

The 'D' suffix on the version of the L298 I want to use, means that it has built-in diodes on the outputs to help counteract any spurious back-emf from the motor in normal operation ie: forward/stop/reverse/coasting. Would there be any further advantage in adding extra external fast schottky 'fly-back' diodes of generous amperage across the motor?....bearing in mind it will constantly be position-controlled by feedback through an external 5k pot through the M51660L's circuitry...therefore not having too much over-run, coasting etc. to deal with?

Can I leave the 'current-sensing' A+B connections (pins 1 + 15) on the L298D not used...what is their purpose?

Would I still need to keep the 560k resistor and 0.1uf cap between pins 2 + 6  in place, as shown on the M51660L schematic?

As I said, I'm new to these...'er... 'little black chips' and their mysteriously complex capabilities, so if I appear like a complete dunderhead in these matters, please excuse me and I apologise in advance for the numerous questions.
If it glows red hot, runs at 500 volts +, has been obsolete since the late 60's, and makes guitars and hifi sound great,
then I'm quite at home.  Valve/tube powered retro-bot anyone...??

I have added data/schematics for both the M51660L and L298D ic's for your perusal.

Many hopeful thanks!

P-90

AttachmentSize
servo-control-circuit.jpg44.71 KB
m51660L_SERVO_CONTROLLER.pdf82.25 KB
L298.pdf185.1 KB
SCHEMATIC_1ST_DRAFT__SERVO_BOARD-bmp.gif30.64 KB

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To answer one of your questions:

No, do not apply your battery voltage to the logic supply (pin 9 Vss) of the L298 chip. To begin with, the data sheet claims the absolute maximum voltage that can be applied is 7V and you say your maximum voltage will be 7.5V which could actually be as high as 8.4V if your using a freshly charged LiPo or Li-Ion battery.

If your homemade servo will be driven by a processor such as picaxe, propeller, arduino etc. then connect their Vcc to this pin so that all the logic is working at the same voltage (make sure logic ground and servo ground are connected together). Otherwise use a 5V regulator to power your RC receiver and the logic circuitry of the servo.

To help you more it would be appreciated if you can supply a complete schematic of your proposed design (M51660 and L298D connected together) along with more information about your setup. What battery are you using and what is the stall current of your motor?

Hello OddBot,

 Thanks loads for taking the time to reply.
I've been hard at work and have just completed a schematic as you suggested, of what I would like to achieve with my DIY RC servo/motor control board.
I would be ever so grateful if you could give it the once-over, and point out any glaring mistakes, I no doubt have made.
I've drawn the schematic mainly from intuition and guesswork, rather than any firm knowledge of what all these bloody
pins do, or how they're supposed to connect to each other!. :>))
My main source of confusion is pertaining to the outputs on the M51660L, and the various inputs/enables on the L298, especially
when it's in paralelled mode for greater current handling.
In the L298 datasheet (fig.7), it shows pin 6 connected to pin 11 - (Enable A+B respectively) for the paralleled mode,
that's ok, I get that, but on the M51660L schematic, pins 4+12 would have connected to the bases of each original 2SA695 transistor either side of the motor's H-bridge to provide forward/reverse operations...If I wire up the L298 (paralleled) as the data sheet says,
how will it know which direction to turn if it's Enable pins (6+11) are commoned like that? Do you know what I mean?...what do I
do with the connection from pin 12 ( ...or pin 4 even?) on the M51660L?. My instinct tells me to make seperate connections to pin 11 from pin 12, (and from pin 4 to pin 6) and I have drawn this in my schematic, but as integrated circuits and their inner workings are pretty much like 'double-dutch' to me, it would not suprise me in the slightest, to see the whole thing go up in a puff of acrid smoke!
Please can you have a look and tell me if I'm at least on the right path. Also, there is provision on the L298 (pins 1+15) for
Current Sense resistor/s...do I need them? If so, what value would be suitable, bearing in mind I'll be running this thing in parallel?.

Many Thanks,

P-90

It looks to me like you could add a self built h-bridge to control said motor. I would imagine you would need to shield the output pins from current, so, you would need transistors there that could handle the current you propose to control.

I am really only answering this in hopes that some of the more knowledgeable will speak up.