PWM fried from servo

[Mschmeh144]

Hello

Due to a recent discussion on another thread, I have decided to see what I can make with out old Tetrix kit and motors. I have mounted a robotic arm to our robot " ghettobot" which is a test bed.
I am not using the bots systems, the arm has its own independent power and controllers, and radio transmitter of the hobby rc type. A Futuba to be exact. Also, using one saber tooth 2*12 motor controller. I ran into a problem, the Tetrix motor runs fine.the arm is a multi jointed arm so the joints all use high tec servos. I cut the end off a PWM and ran it into the screw terminal on the saber tooth, as soon as I powered the system on, the Tetrix came to life " evident by the sudden jerk of the arm" but the PWM cables I used to connect a female PWM to female fried and blew up in smoke. I was told the servos are 5-12v servos, so I see no reason for it to fry like that. I was using a 12v source with a breaker. Please help me, I know I'm probably doing something wrong

[Tungrus]

Servos are typically 6V, atleast the one that come with KOP. 12V will fry them.

[Mschmeh144]

Servos are typically 6V, atleast the one that come with KOP. 12V will fry them.

Thanks. I'm guessing they are the 6v type. The saber tooth has a 5v connection, you need to solder a pin to it though and if you do it wrong you can cause a short through the heat sink. I'm guessing that's how you hook a servo up to it. But I'm not sure

[GeeTwo]

Do I understand correctly that the wires burned up? If so, it seems more likely that you had a mechanical short somewhere, possibly created by the "sudden jerk". A failure of the servo unit due to over-voltage would more likely result in the circuit opening; the wires would have been spared.

[Tungrus]

Servo has electronics inside, applying 12V will burn them. If its not working, the smell will tell you if its a toast.

[Mschmeh144]

Do I understand correctly that the wires burned up? If so, it seems more likely that you had a mechanical short somewhere, possibly created by the "sudden jerk". A failure of the servo unit due to over-voltage would more likely result in the circuit opening; the wires would have been spared.

Yes, they burned up to the point where a smoke cloud formed

[Mschmeh144]

Do I understand correctly that the wires burned up? If so, it seems more likely that you had a mechanical short somewhere, possibly created by the "sudden jerk". A failure of the servo unit due to over-voltage would more likely result in the circuit opening; the wires would have been spared.

I originally thought they burned up the whole wire, but it looks like it just burned up the insulation, now that I've pulled the insulation away from the still intact copper wire. I don't think the servo got toasted, the smell wasn't coming from the servo. No smoke either. Just the 2 wires I used burned up, both positive and negative wires.

[philso]

I originally thought they burned up the whole wire, but it looks like it just burned up the insulation, now that I've pulled the insulation away from the still intact copper wire. I don't think the servo got toasted, the smell wasn't coming from the servo. No smoke either. Just the 2 wires I used burned up, both positive and negative wires.

If the insulation on wires running to the servo burned, then it is a fair certainty that too much current flowed through those wires, more than the servo should draw at any time. Thus there must be something wrong inside the servo, say a short. It is possible to "burn" the copper conductors in the wire if the current was even higher.

[Kevin Sevcik]

I want to make sure we're all clear on exactly what you did and how you wired things. Here's my interpretation:

1. You connected the Futaba R/C controller to the S1 and S2 terminals on the Sabertooth.
2. You connected 2 wires from the tetrix motor to Motor 1 or 2 on the Sabertooth.
3. You cut the PWM connector off a servo and connected the black and red wires to Motor 1 or 2 on the Sabertooth.

Then you powered everything on, and I'm guessing the wires from the servo to the sabertooth melted and the servo went up in smoke, yes?

[Mschmeh144]

I want to make sure we're all clear on exactly what you did and how you wired things. Here's my interpretation:

1. You connected the Futaba R/C controller to the S1 and S2 terminals on the Sabertooth.
2. You connected 2 wires from the tetrix motor to Motor 1 or 2 on the Sabertooth.
3. You cut the PWM connector off a servo and connected the black and red wires to Motor 1 or 2 on the Sabertooth.

Then you powered everything on, and I'm guessing the wires from the servo to the sabertooth melted and the servo went up in smoke, yes?

Somewhat correct. The Tetrix motor was plugged into motor 2. I used a male to female PWM, cut the end off on the male side, and stripped and inserted that side to the motor 1 terminal on the saber tooth, then I used a long PWM male to female connecting to the servos PWM( the arm is hollow so I ran the wire down the inside ). I didn't modify the servo or the wires in any way except stripping one end to plug it into the sabertooth. In between the long PWM wire and the wire connected to the sabertooth I placed two single pin jumper wires, because both ends were female connectors. As soon as I powered on, the arm jerked a little ( that was the Tetrix motor) then using the rc remote I commanded the Tetrix to move. It did not, and then I commaned the servo, and the two jumpers immediately went up in smoke so I ripped them out by hand ( got burnt but it's better than the alternative of setting the building fire suppression off ). No smoke whatsoever came from the servo, and the receiver and sabertooth have their own separate power supplies.

Edit: i cannot get back to the shop until Monday so I cannot inspect the servo and the wiring until then. I'm assuming I did it wrong,I dont think it was the servos fault. When I get back I'll post a photo of the setup I was using ( with replaced wires to show where I put the jumpers ).

[Kevin Sevcik]

So, what you were supposed to do is connect the servo directly (or through an extension) to one of the ports on the Futaba RC. You shouldn't have connected it to the Sabertooth. Read on to see why.

I'm going to start with a (brief) story so you know that I've been there too, then tell you what you did wrong.

Back when I was in high school on a BEST team, we built a small bot with a small arm we wanted to power using servos. To make the mechanical design cleaner, we mounted the servos back to back. Because this was BEST, we wanted to drive both servos with one channel, so we had to figure out how to reverse one of the servos. And I said "It's a motor, we'll just swap the red and the black wires and it'll go backwards!". (Al Skierkiewicz is shaking his head right now if he's reading this. Hi Al!) It didn't work and I ruined a servo and we had to mechanically change the robot and it was a terrible idea anyways.

I was completely wrong and ruined a servo for the same reason your wiring was wrong and smoked: Servos are not motors. There are a fair amount of fancy electronics in there including a potentiometer, motor controller, and feedback controller. The red and black wires provide power to the internal electronics and motor controller. That internal electronics is what powers the servo's actual motor. The white wire carries the signal R/C style signal that tells the servo what position to be in.

When I swapped red and black, it was like swapping red and black on the input power to your Sabertooth. It's a bad thing and ruined something inside the servo. When you connected red and black to the 12V output of your Sabertooth, it was similar to connecting the power input of your Sabertooth to, say, the 120V coming out of a wall socket. Too many volts not doing what's expected. Thus the smoke. I will tell you that even if you connected the Sabertooth to 6V and the servo hadn't smoked, it wouldn't do what you wanted. Changing the voltage on the red and black servo wires doesn't command the servo to move, changing the signal on the white wire does. And once you told the servo to go in reverse, it'd be just like my mistake and would've fried anyways.

Thus you should connect the servo to the Futaba, which provides the correct control signal on the white wire, and should provide the correct power on the red and black wires. I have no idea if your servo is still good, but I'd guess it's not. So find a new one and connect it that way.

TLDR; Servos aren't dumb motors. They're smart motors and their smarts can and will be fried if you connect their power (red/black) to too high a voltage or the wrong polarity. Plus the red/black wires don't control what the servo does anyways.

[Mschmeh144]

So, what you were supposed to do is connect the servo directly (or through an extension) to one of the ports on the Futaba RC. You shouldn't have connected it to the Sabertooth. Read on to see why.

I'm going to start with a (brief) story so you know that I've been there too, then tell you what you did wrong.

Back when I was in high school on a BEST team, we built a small bot with a small arm we wanted to power using servos. To make the mechanical design cleaner, we mounted the servos back to back. Because this was BEST, we wanted to drive both servos with one channel, so we had to figure out how to reverse one of the servos. And I said "It's a motor, we'll just swap the red and the black wires and it'll go backwards!". (Al Skierkiewicz is shaking his head right now if he's reading this. Hi Al!) It didn't work and I ruined a servo and we had to mechanically change the robot and it was a terrible idea anyways.

I was completely wrong and ruined a servo for the same reason your wiring was wrong and smoked: Servos are not motors. There are a fair amount of fancy electronics in there including a potentiometer, motor controller, and feedback controller. The red and black wires provide power to the internal electronics and motor controller. That internal electronics is what powers the servo's actual motor. The white wire carries the signal R/C style signal that tells the servo what position to be in.

When I swapped red and black, it was like swapping red and black on the input power to your Sabertooth. It's a bad thing and ruined something inside the servo. When you connected red and black to the 12V output of your Sabertooth, it was similar to connecting the power input of your Sabertooth to, say, the 120V coming out of a wall socket. Too many volts not doing what's expected. Thus the smoke. I will tell you that even if you connected the Sabertooth to 6V and the servo hadn't smoked, it wouldn't do what you wanted. Changing the voltage on the red and black servo wires doesn't command the servo to move, changing the signal on the white wire does. And once you told the servo to go in reverse, it'd be just like my mistake and would've fried anyways.

Thus you should connect the servo to the Futaba, which provides the correct control signal on the white wire, and should provide the correct power on the red and black wires. I have no idea if your servo is still good, but I'd guess it's not. So find a new one and connect it that way.

TLDR; Servos aren't dumb motors. They're smart motors and their smarts can and will be fried if you connect their power (red/black) to too high a voltage or the wrong polarity. Plus the red/black wires don't control what the servo does anyways.

Thanks for your clarification. The futuba is running off a battery pack with 4-aa cells in it, but those batteries are not reliable enough for me to be running any servos off of. If I'm correct, you can power it using the sabertooths 5v pin right?
Normally, I would not have tried this kind of setup, but I am unfamiliar with this kind of setup.i had to make it I dependant because I didn't want to take a chance of me messing up and frying the control system on the robot its mounted to. I'm guessing the servo is toast. So I just connect it straight to the futuba?
Also, can the sabertooths interface with the roboRio in any way so that I won't need to have two separate systems?

[Kevin Sevcik]

I don't think there's anyone on CD who hasn't done something silly can ended up frying/melting/exploding something before. If they haven't, they probably haven't done much interesting stuff. Just don't make a habit of it, because it gets expensive.

If you had the sabertooth working with the futaba to move the tetrix motor, then the S1 and S2 control signals for the sabertooth should be the same as the control signals for any of the other FRc motor controllers. So yes, you can control the Sabertooth through the RoboRIO. To do so, connect the white wire of a standard PWM to S1 or S2 and the black wire to 0V. Leave the red wire unconnected, but tape it up so it doesn't short the roboRIO to something else. Then plug the female end of the PWM into the RoboRIO just like any other motor controller.

Yes, you can power the Futaba off the 0V and 5V connections on the Sabertooth. They say you can use up to 4 standard servos if you do that, so you should be good.

Also, it used to be standard practice to run entire VEX robots off 6 AA batteries, so running one servo off a handful of batteries isn't a big deal.

[Mschmeh144]

I don't think there's anyone on CD who hasn't done something silly can ended up frying/melting/exploding something before. If they haven't, they probably haven't done much interesting stuff. Just don't make a habit of it, because it gets expensive.

If you had the sabertooth working with the futaba to move the tetrix motor, then the S1 and S2 control signals for the sabertooth should be the same as the control signals for any of the other FRc motor controllers. So yes, you can control the Sabertooth through the RoboRIO. To do so, connect the white wire of a standard PWM to S1 or S2 and the black wire to 0V. Leave the red wire unconnected, but tape it up so it doesn't short the roboRIO to something else. Then plug the female end of the PWM into the RoboRIO just like any other motor controller.

Yes, you can power the Futaba off the 0V and 5V connections on the Sabertooth. They say you can use up to 4 standard servos if you do that, so you should be good.

Also, it used to be standard practice to run entire VEX robots off 6 AA batteries, so running one servo off a handful of batteries isn't a big deal.

Thanks for your help. Hopefully I can get this problem corrected easily, and once I get the arm protoyped working independently I'll try hooking it up to the roboRio and then we will have a robot with a working arm. Should I power the sabertooth off the PDP or should it stay independant ?

[Kevin Sevcik]

Thanks for your help. Hopefully I can get this problem corrected easily, and once I get the arm protoyped working independently I'll try hooking it up to the roboRio and then we will have a robot with a working arm. Should I power the sabertooth off the PDP or should it stay independant ?You should be able to power it off the PDP. You do know the Sabertooth isn't legal on a FRC robot, right? It's fine for prototyping and playing around, but you won't pass inspection if it's on a robot.

[Mschmeh144]

You should be able to power it off the PDP. You do know the Sabertooth isn't legal on a FRC robot, right? It's fine for prototyping and playing around, but you won't pass inspection if it's on a robot.

I am aware that they aren't legal. The arm is mounted on a old testebed bot that itself, isn't first legal (it will be when I'm done with it )
Thanks for the help, I'll be sure to glance over this thread again when I get the chance On Monday.
If I can get the system running I'll post a link to a video of the arm operating

[GeeTwo]

I don't think there's anyone on CD who hasn't done something silly can ended up frying/melting/exploding something before. If they haven't, they probably haven't done much interesting stuff.

Guilty. First noted time, I was two (digging in a 220V wall plate). Most recent, last fall (heated vegetable oil to flash point; second offense). Several dozen in between; it's a bit of a marvel that I got to pass on my genes and learning on to the next generation.

[Mschmeh144]

Update, the servo did fry, took it apart, smells horrible. I did get the arm to work using the rc reciever but it punched me in the face so I dismanlted it. ( Tetrix motors just make my naughty list ). I soldered a pin onto the sabertooth and Wired the futuba up to the 5v and 0v pin and powered it off there. ( the holder for our batteries to power the thing was cheap plastic and finally gave up the ghost ) but it did work. Im scrapping the arm and building a much more durable one after I learned the Tetrix would barely lift the weight of the arm. Any suggestions on what motor I should use are welcome

[GeeTwo]

Any suggestions on what motor I should use are welcome
So much depends on the particulars of the arm length, load (including its own weight) and speed and precision required, as well as the electrical system you're using.

Not being familiar with Tetrix motors, I googled and came up with this (https://www.pitsco.com/Motors/TETRIX_DC_Gear_Motor).

Is this the motor you were using, powered by 5V? It's a 12V motor, and the output power of DC motors (especially gear motors) falls off considerably at low voltage. I would expect that if you use a 12V supply you can get at least an order of magnitude more power than you were getting at 5V. Of course, this would require a relay module or other 12V-capable controller.

If you are powering with 5V, limit your searches to motors designed for 5V or 6V.