Control 2 servos via 1 channel for continuous rotation?

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quadconnect
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Control 2 servos via 1 channel for continuous rotation?

Post by quadconnect » Wed Dec 19, 2018 2:42 am

Hi guys! For a project that I'm working on, I want to be able to control 2 servos very specifcally via a single chanel (throttle).

I know the mixer built into stock openTX on the x9d is pretty powerful, but I'm not sure how to actually use it for a scenario as weird as this one.
Basically, we are trying to enable continual back and forth rotation of two different servos in opposite directions via a single RC channel (throttle).

I don't know if this is programmable via the x9d, or if we would need a seperate microcontroler, though I'd prefer not using one as it cuts down on complexity a bunch.

If you guys have any ideas or places where I should start, let me know!

(Additionally, this might complicate things a bit, but here are the servos I'm going to use. If this does complicate everything because the servos are brushless, you can ignore this part.)

https://www.amainhobbies.com/hitec-hsb9 ... 3/p361358
Thanks so much!
Adi


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Kilrah
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Re: Control 2 servos via 1 channel for continuous rotation?

Post by Kilrah » Wed Dec 19, 2018 9:03 am

If you want a single receiver output channel to control both servos in opposite directions you have no choice but to use an external micro in the model. If you can use 2 channels then no issues with just the radio.

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Re: Control 2 servos via 1 channel for continuous rotation?

Post by pmullen503 » Wed Dec 19, 2018 12:18 pm

You can map the throttle to two channels in opposite directions.

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jhsa
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Re: Control 2 servos via 1 channel for continuous rotation?

Post by jhsa » Wed Dec 19, 2018 12:43 pm

Do the servos work always together but just in opposite directions? If so, you have 3 options.

1 - Use 2 separate channels, but you said you don't want this..

2 - Use a servo reverser on one of the servos, but you also don't want to add external boards..

3- Modify one of the servos. that means (I think) reverse the motor polarity. If the motor is brushless you would have to reverse/swap only 2 of its connections. Search online, I think there are tutorial explaining how to do it..

I did something similar when I built some retracts for my old quadcopter..

https://www.youtube.com/watch?v=vEcZBgX ... DzhK7&t=0s

https://www.youtube.com/watch?v=U-zZNs5 ... DzhK7&t=0s

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Re: Control 2 servos via 1 channel for continuous rotation?

Post by Kilrah » Wed Dec 19, 2018 2:02 pm

jhsa wrote:
Wed Dec 19, 2018 12:43 pm
3- Modify one of the servos. that means (I think) reverse the motor polarity.
You also need to reverse the sensing aka outer wires of the pot.

The brushless motor may be sensored, in which case there would be more stuff to take care of there.


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Re: Control 2 servos via 1 channel for continuous rotation?

Post by jhsa » Wed Dec 19, 2018 4:12 pm

as far as I know, when modifying servos for continuously rotating, the pot is replaced by 2 resistors of equal value, as if it was centered. So, the pot is not used anymore obviously :)
I haven't had a look how the brushless servos work, but I am sure google might have some answers and tutorials ;) :)

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Re: Control 2 servos via 1 channel for continuous rotation?

Post by Kilrah » Wed Dec 19, 2018 7:07 pm

You misunderstood the way he talks of "continuous rotation". He apparently just wants continuous back and forth motion within the nornal servo range, not the mod-requiring 360° rotation.

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Re: Control 2 servos via 1 channel for continuous rotation?

Post by pmullen503 » Wed Dec 19, 2018 11:11 pm

Looking at the servo he wants to use, the servo can be programmed in terms of direction so one channel and a Y connector seems to be all that's required.

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Re: Control 2 servos via 1 channel for continuous rotation?

Post by jhsa » Wed Dec 19, 2018 11:18 pm

Kilrah wrote:
Wed Dec 19, 2018 7:07 pm
You misunderstood the way he talks of "continuous rotation".
It looks like I did. Sorry about that.. ;)

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Re: Control 2 servos via 1 channel for continuous rotation?

Post by quadconnect » Fri Dec 21, 2018 2:44 am

Ok, first of all, thanks so much to all of you guys for all the responses and help!

Let me clarify a bit. Before I try to reverse the direction of a second servo, or even include a second servo at all, let me focus on the first task.

Do you guys know if there is any possible way to enable a single, normal, 180-degree servo for continuous back and forth rotation within its normal 180 degree range with the use of a single channel like throttle?
Ideally, I would just be able to push the throttle stick up and have the servo go back and forth automatically. 'More throttle' (stick is pushed up higher) would mean the servo would move back and forth faster.

I don't know if that's even possible. This is for an ornithopter, by the way. And when I say separate microcontroller, I meant something like an arduino or feather board. A servo direction reverser is totally fine haha.

If we can get a single servo with back and forth rotation, it shouldn't be too difficult to add a second servo to the same channel but have its direction reversed using the mixer (I think).

Thanks so much again for all the help!
Adi

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jhsa
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Re: Control 2 servos via 1 channel for continuous rotation?

Post by jhsa » Fri Dec 21, 2018 3:02 am

So, the servo just moves back and forth between its maximum travel points, and this movement just gets faster and faster when you move the throttle upwards..

What confused me earlier was the continuous rotation thing.. :(

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Re: Control 2 servos via 1 channel for continuous rotation?

Post by quadconnect » Fri Dec 21, 2018 3:09 am

jhsa wrote:
Fri Dec 21, 2018 3:02 am
So, the servo just moves back and forth between its maximum travel points, and this movement just gets faster and faster when you move the throttle upwards..
Yep! I don't know if that's possible to implement with a opentx though....?

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Re: Control 2 servos via 1 channel for continuous rotation?

Post by ReSt » Fri Dec 21, 2018 4:12 pm

I found a solution with ERSky/ER9x that I believe does what you are looking for. I dont know if opentx has a similar function (Latch with set/reset).

I set up a logical switch (L6) as a latch with a SET (L1) and a RESET (L2) condition. It is set, when the output channel, in my example ch07, is > 99 and reset when the channel value is less than -99.
With this switch, a +Add or -Add mixline is activated and added to the value of channel 7.
ch7 = 100% ch7 means, that the channel holds its value when there is no activity.
ch9, due to the (early) offset, deliveres a value from 0 to 100
The speed of the motion is controlled with Thr stick


ch7 = +100% ch7 notrim
+ 10% ch9 Switch(!L6) notrim
- 10% ch9 (Switch(L6) notrim
ch9 = +50% Thr notrim offset(100%) (don't activate fixed offset)

L1 v>val ch7 99
L2 v<val ch7 -99
L6 Latch L1 L2

I only tried it in the simulator of eePskye

Reinhard

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jhsa
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Re: Control 2 servos via 1 channel for continuous rotation?

Post by jhsa » Fri Dec 21, 2018 5:05 pm

Cool :) I wouldn't get there myself. I think it is exactly what he wants. But you can use "Fix Offset" if you do like this.

ch9 = +50% Thr notrim offset(50%)

And it makes sense. :)

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Re: Control 2 servos via 1 channel for continuous rotation?

Post by ReSt » Sat Dec 22, 2018 10:13 pm

João, that's correct :D

And I found a solution for OpenTx also.
It works with the sticky function

ch7 = ch7 Weight(+100%)
+= ch9 Weight(+10%) Switch(!L1)
+= ch9 Weight(-10%) Switch(L1)
ch9 = Thr Weight(+50% Offset(50%)

L1 Sticky L2 L3
L2 a > x CH7 99
L3 a < x CH7 -99


Reinhard

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jhsa
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Re: Control 2 servos via 1 channel for continuous rotation?

Post by jhsa » Sat Dec 22, 2018 10:22 pm

Cool :)
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