Servo Mixing Circuit

[Talon Driver]

I have a project requiring mixing servos for different modes.

A project well beyond my JR 8103 TX.

Anyone know of a circuit schematic for analog or digital servos?

I also am looking for a circuit schematic for mixing components on board the aircraft? e.g. Mode 1 (1 ms pulse) I send role signal serialy through role gyro and lift fans, Mode 2 (1.5 ms pulse) I send yaw signal serialy through yaw gyro and lift fans.

No need to get into all the details here.

Again looking for two electronic circuit schematics, one for servos and another for any known mixing device.

I have a fairly good grasp of these fundamentals having taken several control courses (actually making a servo out of an electric motor). So I want DETAILS, no concepts.

Cheers,

Chuck

[steve lewin]

I'll move this to the DIY Electronics forum. It's just the place for this sort of topic though you might have to provide a few more details of what you're trying to do before anyone can help.

There are loads of PIC-based mixer circuits about. See the links thread at the top of the forum.

Steve

[Ironsides]

Chuck:

Anything here that is in the same ballpark?

http://www.rc-float-flying.rchomepage.com/RCWeb/PIC/Ironsides.htm

David

[Comatose]

Talon, if I understand you correctly, you want to be able to use a tx switch (third channel) to turn mixing on and off on different systems. Is this correct? What happens to the other channel when the switch is in the "other" position? Holds?

Or, are you looking to cut either your roll or yaw gyros out of the loop and just directly control the channel that isn't under gyro control.

If that's the case, the way I'd do it would be as follows. A pic12f675 won't cut it here, I'd go to a pic18f1220.

Basically, set up pulse measurement for five channels. Two of them will be your roll and yaw inputs. One will be your switch. The other two inputs are the outputs from your gyros.

Essentially the code would be to read the position of the "switch" channel, then based on that make the output either be identical to the input from your TX or the input from your gyro.


I've actually been kicking around the idea of making a computer-programmable ultra free mixer and trying to sell it for about $50 for 5 channels. Essentially you'd get a board which you could program via a little GUI to do basically whatever you wanted.Mix 5 channels into 1, switch between mixing modes, conditional mixing (only mix flaps and throttle above a threshhold or something). If one existed would you be interested? I figure I need reasonable confidence that I could sell 30 to make it worth doing.

[jeffs555]

Comatose,
With the new Hummingbird collective pitch heli available so cheaply, there might be a market for such a mixer. I have a CP HB on order, but my current transmitter doesn't handle CCPM mixing, and I am sure I am not the only one. I am programming an AVR to do the mixing. I had thought about building them for sale, but probably won't. With the programming cable, and all the connectors to the receiver, it would be fairly labor intensive to build, but with a good GUI, like you say it would be extremely versatile.

Jeff

[Talon Driver]

First, what is a PIC. That is what do the letters "P" "I" "C" stand for? Then please provide a single sentence definition.

Again I am very familiar with very basic electronic ciruits, Operational Amplifiers, transistors, capacitors, resistors, inductors and input output functions.

Anything that is commercial off the shelf from today's electronics and I am afraid you need to explain your NOMENCLATURE.

Also, what is a "CB" and "HB"?

Please no abbreviations.

Cheers,

Chuck

[Talon Driver]

I've actually been kicking around the idea of making a computer-programmable ultra free mixer and trying to sell it for about $50 for 5 channels. Essentially you'd get a board which you could program via a little GUI to do basically whatever you wanted.Mix 5 channels into 1, switch between mixing modes, conditional mixing (only mix flaps and throttle above a threshhold or something). If one existed would you be interested? I figure I need reasonable confidence that I could sell 30 to make it worth doing.

I like the sounds of this.

I am afraid I do not understand your other questions.

Here are some of the features that I would like to put in circuit or out of circuit:

Mode 1

Receiver Throttle -- Role Gyro -- Electronic Speed Control to Left Motor
Receiver Aux 1 -- Role Gyro (Inverted Signal) -- Electronic Speed Control to Right Motor
Receiver Elevator -- Pitch Gyro -- Tail Lift Fan

Mode 2

Receiver Throttle -- Yaw Gyro -- Electronic Speed Control
Receiver Aux 1 -- Yaw Gyro (Inverted Signal) -- Electronic Speed Control to Right Motor
Receiver Elevator -- Pitch Gyro -- Elevator Servo

Mode 3

There is a mode 3 but I do not need to get into it here.

Bottom line I need an on-board circuit that has a dedicated receiver channel that commands it to go to Mode 1 or Mode 2 or Mode 3.

e.g. Receiver Aux 2 signal of 1.1 miliseconds = Mode 1, 1.5 miliseconds = Mode 2, 1.9 miliseconds = Mode 3

Cheers,

Chuck

Cheers,

Chuck

[jeffs555]

Chuck,
PIC is a brand of microcontroller made by Microchip Corporation. The functions you want to do sound pretty complex, and are probably best done by a microcontroller. I am not quite clear whether you actually want to combine two or more receiver outputs together(ie mixing), or if you just want to switch different receiver outputs to different servos based on the signal from another receiver channel. If you just want to switch different receiver channels to different servos at different times, it could be done with resistors, capacitors, gates and op amps. If you want to mix receiver channels together so that the signal to a servo is composed of different percentages from several receiver channels, then it is much more complex, and you probably need a microcontroller with a custom program.

I don't know of any design available now to do what you want. The device that Comotose is talking about would do it, since it would be so user configurable. You just have to convince him that it is worth his time to produce it.

Jeff

PS HB(HummingBird) is a brand of helicopter, and CP(Collective Pitch) is a type of rotor control for helis that requires specialized mixing.

[mike50]

First, what is a PIC. That is what do the letters "P" "I" "C" stand for? Then please provide a single sentence definition.

Again I am very familiar with very basic electronic ciruits, Operational Amplifiers, transistors, capacitors, resistors, inductors and input output functions.

Anything that is commercial off the shelf from today's electronics and I am afraid you need to explain your NOMENCLATURE.

Also, what is a "CB" and "HB"?

Please no abbreviations.

Cheers,

Chuck

PIC is a trademark of the Microchip company which refers to the line of single chip microcontrollers that they make. I don't know if the individual letters mean anything.

"CP" (not CB) stands for Collective Pitch (a type of helicopter rotor head)
"HB" stands for HummingBird (an electric helicopter)

[Talon Driver]

Chuck,
PIC is a brand of microcontroller made by Microchip Corporation. The functions you want to do sound pretty complex, and are probably best done by a microcontroller. I am not quite clear whether you actually want to combine two or more receiver outputs together(ie mixing), or if you just want to switch different receiver outputs to different servos based on the signal from another receiver channel. If you just want to switch different receiver channels to different servos at different times, it could be done with resistors, capacitors, gates and op amps. If you want to mix receiver channels together so that the signal to a servo is composed of different percentages from several receiver channels, then it is much more complex, and you probably need a microcontroller with a custom program.


Jeff,

Switching is really all that I need. I do not need mixing since I will be able to do all the mixing that I require on my JR 8103.

So do you know of any circuit diagrams anywhere that I can use for this?

Also I realized that I have a Computer Dictionary. This refreshed my memory a tremendous amount.

You sure that PIC doesn't also mean Programmable Interrupt Controller? It looks like these PIC circuits are EEPROMS that perform certain programmable commands until they receive an interrupt where upon they switch to a different set of instructions, hence Programmable Interrupt Controllers (PIC).

Cheers,

Chuck

[Comatose]

Talon, that may have originally been the aconym for all I know, but anymore its just a name, just as AVR is just a name or a pentium is just a name. You certainly don't "need" to use any interrupts when working with PICs, and in fact many hobbyists don't, which is fine I guess. Pics also certainly aren't the only micros with interrupt capabilities. The real reason that they're the standard for prototype/hobby type work is that microchip embraced the guy who is only ever going to need three well before most companies caught on. Motorola 68000 derivatives and 8051 derivatives are still more common in commercial designs, though.

The real issue with making the programmable free mixer (the time consuming bit) isn't the circuit layout or the interfacing or even the GUI. The real problem is writing the scripting language/compiler/interpreter/bytecode interpreter. That could be really easy or really hairy, depending on how complicated the functionality needed is. I was thinking something kinda like Simulink for an interface, where you'd have addition blocks and gain blocks and conditional blocks, then link them up graphically.

The issue becomes how free are the free mixes allowed. If it was essentially a fixed-function additive scheme, that'd be a piece of cake to do. (channel1out = X1*channel1in+X2*channel2in + X3*channel3in +...)

It'd be a little trickier but still pretty easy to add limited conditionals like

if(channel3 > 90): channel1out = X1*channel1in+X2*channel2in + X3*channel3in +...
else: channel1out = Y1*channel1in+Y2*channel2in + Y3*channel3in +...

But thats still only a couple days worth of coding. Something like the following would take a bit more doing to do
Channel1out = channel1in*(channel2in - channel3in)/channel4in
if(channel5in > channel6in): channel1out = channel1out-channel7

Doing that would take a much more advanced interpreter, and it'd probably be smarter to just write a little compiler for it.

Also, multiplies would be pretty handy, because then instead of dual rates you could have analog rates, where you dial in your throws un flight. I just haven't figured out what to do if, say, you have three bi-directional channels (R/E/A) and you multiply them all together. The results (at least the sign of the results) would be... unpredictable at best. Current mixing schemes are pretty much all additive. Maybe only unidirectional multiplies? Throttle, switches and pots are unidirectional. The main three axes are bidirectional.

Can anyone think of a good reason to multiply, say, rudder and elevator? A normal V-tail mix looks like below, and doesn't multiply the channels

channel1 = channel1in - channel2in
channel2 = channel1in +channel2in

pretty basic. A fixed-functionality 5 channel mixer you'd get boxes in a GUI that looked like the following

Channel 1: ____%InOne +____%InTwo +____%InThree +____%InFour +____%InFive
Channel 2: ____%InOne +____%InTwo +____%InThree +____%InFour +____%InFive
Channel 3: ____%InOne +____%InTwo +____%InThree +____%InFour +____%InFive
Channel 4: ____%InOne +____%InTwo +____%InThree +____%InFour +____%InFive
Channel 5: ____%InOne +____%InTwo +____%InThree +____%InFour +____%InFive

So an elevon mix would look like

Channel 1: 100_%InOne +-100%InTwo +__0_%InThree +__0_%InFour +__0_%InFive
Channel 2: 100_%InOne +100_%InTwo +__0_%InThree +__0_%InFour +__0_%InFive
Channel 3: __0_%InOne +__0_%InTwo +_100%InThree +__0_%InFour +__0_%InFive
Channel 4: __0_%InOne +__0_%InTwo +__0_%InThree +100_%InFour +__0_%InFive
Channel 5: __0_%InOne +__0_%InTwo +__0_%InThree +__0_%InFour +_100%InFive

A free functionality mixer you'd script (with function boxes) so essentially

[Channel1in] ------[+-]--------[channel1out]
[Channel2in]_______/

which would be more useful? Option 1 (or a more complicated set of functionality, with one multiply per line or one per item, and one conditional per line or per item) would be easier for everyone concerned. Option 2 would be a pain for everyone but extremely powerful once it was working.

[ElectroLawndart]

I believe that PIC stands for Programmable Integrated Circuit. PIC's are designed to replace a handful of discrete components with one chip.

[Talon Driver]

Jeff,

Switching is really all that I need. I do not need mixing since I will be able to do all the mixing that I require on my JR 8103.

So do you know of any circuit diagrams anywhere that I can use for this?


Anyone know of any off the shelf circuits that can perform switching for RC applications?

For example:
Mode 1 puts a gyro into series between the receiver and the servo
Mode 2 puts a different axis gyro into series between the receiver and the servo

Cheers,

Chuck

[mike50]

I looked it up on Microchip's website.

PIC == Peripheral Interface Controller

Not really very meaningful. I see it as just a name.

Whether you want to do mixing or switching, programming a PIC (or other microcontroller) to do the job you want will almost always be cheaper and smaller than any other circuit you might build. Especially if you use the parts that don't require an external clock. For example, a minimal switch such as you suggest could probably be built with one PIC12F629 and no external components. You might want to add a bypass capacitor and maybe a current limiting resistor on the input, but it can work without those.

Mike

[steve lewin]

If I understand correctly you don't just want what most us call switching you actually want to use the output of one channel on the RX to route the outputs of the other channels to different devices in 2 stages e.g. sometimes Ch x goes to Pitch gyro then one servo, sometimes to the same gyro but a different servo etc.

I've never seen a circuit to do anything like that but it's certainly complex enough to be worth using a microcontroller and you may still need some additional hardware to handle the fact that you sometimes want to switch not only where the Rx signal goes to initially but also where the output from that device goes to.

Steve

[Ironsides]

Chuck:

Are you trying to build a VTOL - something like the Harrier?

David

[Talon Driver]

Chuck:

Are you trying to build a VTOL - something like the Harrier?

David

Yes and no.

I am doing an analysis of alternatives of technical solutions for certain design features of a VTOL that are proving to be the crunch points (where the technology needs to be developed).

If I am able to do this then I definately make it a reality.

At this moment it is strictly a concept.

I am not rushed.

I plan on putting to use my acquisition training as a program manager in the US Air Force.

Cheers,

Chuck

[Sebax]

Hola, todo mal. PIC = "Peripheral Interface Controller". Es un nombre que le dio en los 80's General Instruments. Hoy por hoy es un nombre que casi no significa nada..