I Can't Use Servo With TeleMega

[Usain]

I'm building a model rocket.
I bought a TeleMega V5. I need to trigger 2 servo motors for the rocket's separation system. but I can't find information for using servos with telemega. How do I run the servos?

 

[Reinhard]

Per the documentation (Release Notes V1.6.2) the hardware and SW drivers support the servos, but the rest of the SW doesn't. V1.6.2 got released a couple of years ago. I couldn't find a newer reference to servos or anything that looks like recent servo related work in the git repo, but I didn't look too hard and might have overlooked something.

I suggest you get in touch with Bdale or Keith to get confirmation for that though.

There are options how you can work around the limitations.
If you feel comfortable to add the missing pieces to the code base, you can attempt that yourself because everything is open source.
Another option is to use a servo controller that can be triggered by the pyro channels. One example is the Sparkfun Servo Trigger. Connect GND on both boards together and connect the IN-input on the trigger with the fet_a (or fet_b, ...) outputs on the TeleMega. Although it might work without, adding a pull-up resistor (10k or less) is highly recommended. You can also add current limiting resistors and/or use opto-couplers. The schematics for both boards can be found here and here. Be careful when connecting the pyro outputs to other electronics. If you're doing it wrong there is quite a chance that something gets damaged. You can always ask here if you're not sure.

Reinhard

 

[Usain]

Per the documentation (Release Notes V1.6.2) the hardware and SW drivers support the servos, but the rest of the SW doesn't. V1.6.2 got released a couple of years ago. I couldn't find a newer reference to servos or anything that looks like recent servo related work in the git repo, but I didn't look too hard and might have overlooked something.

I suggest you get in touch with Bdale or Keith to get confirmation for that though.

There are options how you can work around the limitations.
If you feel comfortable to add the missing pieces to the code base, you can attempt that yourself because everything is open source.
Another option is to use a servo controller that can be triggered by the pyro channels. One example is the Sparkfun Servo Trigger. Connect GND on both boards together and connect the IN-input on the trigger with the fet_a (or fet_b, ...) outputs on the TeleMega. Although it might work without, adding a pull-up resistor (10k or less) is highly recommended. You can also current limiting resistors and/or use opto-couplers. The schematics for both boards can be found here and here. Be careful when connecting the pyro outputs to other electronics. If you're doing it wrong there is quite a chance that something gets damaged. You can always ask here if you're not sure.

Reinhard

Thanks. I ordered 2 sparkfun servo triggers. I need to run 2 servos at the same time. we are preparing for a competition and we have very little time left so I ordered 2 sparkfun to avoid risk.

I'm considering using the apogee output on telemega. I will connect 2 sparkfuns in parallel and hope it will trigger the servos with current from the apogee output. i am new to this stuff. Is there anything I should watch out for? How should I proceed?

 

[Usain]

I'm measuring A B C D and apogee and main all outputs. it gives 4 volts from all of them. it should act like a key now. I don't understand what is the problem. telemega needs to turn sparkfun on and off but it doesn't.
@Reinhard what can I do?

 

[Reinhard]

Where exactly are you measuring your voltages, in reference to what (GND I assume)?

Please use the designators from the schematic (e.g. "J1-3" for connector J1, pin 3) that I posted. Otherwise it's impossible to understand what you are doing.
Also, what are the connections that you made so far. E.g. is the Arming switch connected between J1-7 and J1-8?

Reinhard

 

[Usain]

There is a gnd on apogee output.

Let me tell you what I'm doing now.
I connected the apogee + and - to the starfun servo trigger board. I connected a lipo battery to the servo trigger. The servo trigger is also connected to the servo.
The servo trigger actually works with a power button. but I put telemega instead of power button. but telemega doesn't do this function. When I measure with a multimeter on gnd+ and gnd- it gives 4 volts.

 

[Usain]

There is a gnd on apogee output.
View attachment 529926
Let me tell you what I'm doing now.
I connected the apogee + and - to the starfun servo trigger board. I connected a lipo battery to the servo trigger. The servo trigger is also connected to the servo.
The servo trigger actually works with a power button. but I put telemega instead of power button. but telemega doesn't do this function. When I measure with a multimeter on gnd+ and gnd- it gives 4 volts.

 

[mikec]

What are you powering the servo trigger board with? It's intended for 5V power and has no onboard voltage regulation, though it may work at lipo voltages. Similarly the servos are expecting 5V but may work with less.

You need to have the trigger board powered all the time and hook up the Telemega output to the trigger port correctly.

 

[cerving]

Typically servos require a separate battery from the flight computer, with some capacitor filtering to help keep motor noise out of the flight computer's GND line. Depending on the flight computer, you may or may not need resistors in series with the deployment outputs, or the flight computer may have a "logic level" output that can tie directly to the servo's signal input. You may also need a resistor across the deployment terminals to give it "continuity"... again, that depends on the flight computer. If you're trying to power the servo from the same battery as the flight computer, you may see erratic servo behavior, and it's possible that if the servo stalls it may drag down the voltage enough to reset the flight computer.

 

[OverTheTop]

What are you powering the servo trigger board with? It's intended for 5V power and has no onboard voltage regulation, though it may work at lipo voltages. Similarly the servos are expecting 5V but may work with less.

You could use a 2s (or higher) battery with a small BEC or SBEC to get the 5V.

Typically servos require a separate battery from the flight computer, with some capacitor filtering to help keep motor noise out of the flight computer's GND line. Depending on the flight computer, you may or may not need resistors in series with the deployment outputs, or the flight computer may have a "logic level" output that can tie directly to the servo's signal input. You may also need a resistor across the deployment terminals to give it "continuity"... again, that depends on the flight computer. If you're trying to power the servo from the same battery as the flight computer, you may see erratic servo behavior, and it's possible that if the servo stalls it may drag down the voltage enough to reset the flight computer.

Good advice

 

[cerving]

BTW, if you use a 5V converter with your 2S Lipo for the servo, make sure it will put out at least 1A. A 7805 regulator with the appropriate filter caps should work. That assumes you're using micro or mini sized servos... larger ones may require more power.

 

[Reinhard]

There is a gnd on apogee output.
View attachment 529926
Let me tell you what I'm doing now.
I connected the apogee + and - to the starfun servo trigger board. I connected a lipo battery to the servo trigger. The servo trigger is also connected to the servo.
The servo trigger actually works with a power button. but I put telemega instead of power button. but telemega doesn't do this function. When I measure with a multimeter on gnd+ and gnd- it gives 4 volts.

The 4V that you're measuring are from the sensing circuit in the TeleMega.

You need to connect the boards differently. The TeleMega, like most altimeters, uses low side switches, but luckily that's also how the switch input works.
Besides the battery aspects mentioned above, you need to make at least the following connections (power pins etc. omitted, because I'm lazy). Note that you don't use the "+" outputs on the TeleMega.



But I'd recommend the following connections:


R1 supports the internal pull-up in the Servo Trigger that needs to act against the pull-down resistors in the sensing circuit of the TeleMega. R2 limits your current in case you're miss-wiring something and it should help you prevent damages.

If it still doesn't work, also, check the settings on the TeleMega. By default, they trigger the output only for short period of time, which may or may not be enough to trigger the Servo Trigger, depending on how the input is debounced.

By the way, the TeleMega will signal you that there is no igniter continuity, if you do it this way.

Reinhard

 

[Usain]

Thank you very much. it worked. but the apogee output closes the switch for a very short time. this is insufficient for the servo to turn on. it should turn us off for 1 second. I am able to set the duration in pyro outputs. I think I will use D output instead of apogee output.

 

[Usain]

Our rocket will open the parachute, reaching the apogee point at 5000 feet. How do you think I should do the settings? I am using Pyro Channel D.

 

[Reinhard]

You can use "Flight state after" and select "Coast" from the drop down box. You can also use "Ascent rate less than (m/2)" and enter zero.
If you select multiple conditions, everyone needs to be fulfilled, so be careful what you select, otherwise, the event might not happen.

Reinhard

 

[Usain]

Thank you for everything. The launch will take place in a few days.

 

[Reinhard]

Thank you for everything. The launch will take place in a few days.

Good luck for your flight!

Please test and review everything carefully. Your configuration is a bit unusual and I hope we haven't overlooked anything.

Let us know how the flight went (pics or it didn't happen )

Reinhard

 

[Usain]

Due to a problem in the competition area, our flight was made without avionics. the aerodynamics of the rocket was fine, it flew well without wobble. I have included the video shot by Roketsan, one of the supporters of the competition, above.