Controlling GeekServos with standard Lego PF electronics?

[gyenesvi]

Hope this question is okay here, and that there are some people with electronics background who might be able to give me some hints on this one.

I have been thinking for a while now how great it would be to use Geekservos in my builds. They are quite small, seem to be strong enough, have bidirectional outputs and the housing is designed to be built into lego technic. I thought the only missing piece is that they have a standard RC servo plug instead of a Lego connector. First I thought that's strange, as it should be easy enough to swap. But as I read up on the subject, I realized that the problem is in the way they are controlled; they use a different PWM encoding than the Lego servo does. As I have read, RC servos nowadays use something called PWM frequency modulation (changing the frequency / pulse-width dictates their position, typically 0.5 ms - left, 1.5 ms - center, 2.5 ms - right), at 5-6V. However, the Lego PF servo uses PWM duty cycle modulation (the change in the duty cycle (PWM fill rate) dictates position, furthermore, 2 wires are required for the 2 directions), at 9V. This is probably because lego PF wants to use the same control technique for all their motors, and duty cycle modulation is what is used for DC motors typically, at least this what I gather, and this way DC motors and servos are interchangeable on any PF port. In fact, the lego PF servo is more like a DC motor with a rotary encoder that does the positioning somehow.

So the question is if there exist (readily available) electronic circuits for converting from the duty cycle modulated PWM signal of PF receivers into the frequency modulated signal that a regular RC servo needs? I haven't found anything like that on the internet, neither in hobby electronics shops here, though I am not even sure what words/names to use for the search. The 9V to 5-6V conversion should be easy to account for I guess with a step-down converter.

I am aware that another possible solution for incorporating GeekServos is to ditch the PF system, use a proper RC system with radio receiver and an ESC, and put the GeekServo directly onto the receiver and other lego motors onto the ESC. That works, I have tested it, but that uses a lot of non-lego electronics and results in a mixed system where DC motors run from ESCs and servos run directly from the receiver. Would be great if the GeekServos could work with standard lego electronics as well by adding some sort of converter in between.
 

[2GodBDGlory]

Good question! I don't have much helpful to say, other than that it seems like the sort of thing a custom Arduino program might be able to do, though I have virtually no experience with those

[glowytheglowbug]

i mean u might be able to use PU to do that but for PF i dont think so unless u get the signal from an IR reciever, send it thru an arduino and control respectively

[dr_spock]

Are you looking to use the PF IR remote or PF IR speed remote to control the GeekServos? 

[oracid]

9 hours ago, gyenesvi said:

GeekServos is to ditch the PF system, use a proper RC system with radio receiver

Precisely, that’s the goal!
I used Gray GeekServo in my creations. These are excellent servos that can do a true 360°.
You can do a lot of things with these servos, even a quadruped with 12 DOF.
I campaign for the mixture of Lego, Arduino, RaspPi, RC technologies. This multiplies our creative possibilities by 100.

GeekServo - real 360° - Programming - LEGO Technic, Mindstorms, Model Team and Scale Modeling - Eurobricks Forums

12DOF-Q-3 Quadruped whith GeekServos - LEGO Technic, Mindstorms, Model Team and Scale Modeling - Eurobricks Forums

8DOF-Q-3 - Quadruped line follower with Huskylens. Training for TRR contest 2022 - In my garage - LEGO Technic, Mindstorms, Model Team and Scale Modeling - Eurobricks Forums

[gyenesvi]

13 hours ago, 2GodBDGlory said:

it seems like the sort of thing a custom Arduino program might be able to do

I don't want a programmable solution, but a hardwired electronic one. This should be something small that has an RC plug (soldered) on one side for the GeekServo, a PF plug (soldered) on the other side to connect to the receiver/Buwizz, and the converter circuit in between. And I'd want to use that with multiple GeekServos of course, so it shouldn't be too big :)

10 hours ago, glowytheglowbug said:

unless u get the signal from an IR reciever, send it thru an arduino and control respectively

If I get the signal from an IR receiver, then I don't need the Arduino, because the GeekServo can be controlled directly from the receiver. But I want to do it without an RC receiver..

9 hours ago, dr_spock said:

Are you looking to use the PF IR remote or PF IR speed remote to control the GeekServos? 

Well it should be independent of the remote, but eventually I'd do it with a Buwizz + mobile phone / gamepad controller.

7 hours ago, oracid said:

I campaign for the mixture of Lego, Arduino, RaspPi, RC technologies.

I know that is possible and it's working for me as well, and agree that they are really useful for certain (more advanced) projects. But I'm interested in the possibility of using them in simple builds like RC cars, without requiring too much custom electronics (and a mess of wires).

[oracid]

5 hours ago, gyenesvi said:

without requiring too much custom electronics

In all my projects, the only electronics I do is soldering switches.
A microcontroller card is exactly what is needed to eliminate the complexity of electronics.