i’m looking to use the 12 volt dc 560 lbs. thrust linear actuator from robotshop product code RB-Sct-204 in a set up. the actuator has a potentiometer built in to supply the neccesary feedback to use it in a controlled system. basically i need to control the position, direction, and hopefully speed of the actuator based on my manual movement of a rotary type potentiometer. i know i need a controller and drive but i’m somewhat new to this so i’m not sure how to currectly match these things up. both the control and drive shoud be digital, and as small in size as possible. any help or direction would greatly appreciated. thanx
Hopefully this will explain it better than we could:
en.wikipedia.org/wiki/Duty_cycle
Simply put, don’t run the motor too long and without breaks.
If there is current going to an actuator, it is considered “in operation”, so the “rest” time would be when the actuator is not on.
Manufacturer:
We have contacted the manufacturer and will get back to you shortly.
Which actuator do you have / are considering? It’s possible that the potentiometer operates at a different voltage and as such the two wires are V and Signal (and the GND wire is common).
Unfortunately the manufacturer does not provide the operating current (which also depends on the force exerted). Fortunately the suggestion of using a 20A fuse provides some idea. Normally stall current is about 4 times that of no load, which in this case would be 12A. Given their 20A fuse suggestion, you should choose a ~10 to 15A motor controller.
The actuator operates at a nominal 12V but can accept 6-12V. The LAC can’t be used because it cannot provide the current.
No, since the actuator is not controlled like a servo - a servo needs a 5V timed pulse of between 500 and 2500us, repeated every ~20ms. This actuator simply has potentiometer feedback, which means something outside of the actuator needs to monitor its position and control the motor controller speed and direction accordingly (best done with a microcontroller).
Feedback is always welcome.
RB-Sct-204 is a beast of an actuator, so the LAC could not be used (can’t provide enough current). Unfortunately this means you’d need to program a microcontroller and also purchase a DC motor controller. If you did not need position (only direction and speed), a DC motor controller would be enough. Here’s a tutorial on how to choose a motor controller.
That combination should work indeed
They are 15 amp slow blow fuses.
You can find more information about them in the RB-Spa783’s product manual, which is available under the Useful Links tab on this page:
I double checked the schematics and A0 is in fact reserved internally for measuring the battery voltage and not available like it usually is. You can use A2 instead without changing your design.
The digital calculations aren’t exactly being sent to the actuator: they are taking place inside the microcontroller which in turns sends the appropriate signals to its onboard motor controller. The motor controller is generating the appropriate DC voltages on the Moto_L terminal to make the actuator move in one direction or the other at a specific speed.
That’s right: you would connect one of the potentiometers (e.g. the actuator feedback) in A0 and the other (e.g. the rotary potentiometer) in A1, and yes you can plug both potentiometers onto the same 5V and GND pins.
Your power source does plug into the motor controller board (to the VBAT-GND terminal), and your actuator will plug into one of the motor outputs (e.g. Moto_L).
The voltage regulator (5V) only regulates the power for the on-board Arduino microcontroller and other logic, so it is does not affect the power given to the actuator : the actuator will still use the full 12 volts.
The two “pot reference” wires are the two ends of the internal resistor of the potentiometer.
It’s important that the wiper wire is used properly, but the two reference wires can be inverted with no concern, from an electrical standpoint at least. Changing the order of the two wires does mean that the rotary potentiometer for the control will behave in the opposite manner (a.k.a. inverted) as the other configuration, but it is up to you if this is important or not: it’s only a question of preference of the behaviour, and not a risk of causing any electrical damage.
Yes, we forgot to say that the red(+) and black(-) wires from the actuator are actually for the DC motor of the actuator. These two wires should be connected to the two screws on the Moto_L terminal on the motor controller. Like the potentiometer, the order of the two wires are interchangeable with the consequence of also inverting the direction of movement. It is important however that once the order is determined, that your Arduino program moves the actuator in the right direction to reach it proper set point.
The remaining three wires from the actuator are for the potentiometer, like we discussed above. For the other pot with three leads, your explanation sounds correct. Was the part purchased at RobotShop? If you give us the part number, we can verify for you.
Yes, a sensor with ratiometric output is exactly what you are looking for. Unfortunately not all manufacturers explicitly specify if their sensors are ratiometric, but this is usually the case for potentiometers and they will be labeled otherwise if they are not.
We hope this helps,
The RB-Spa-783 is designed for use with 7.2 volt batteries, but can be used with supplies up to 18 volts. If someone uses a supply is more than 12 volts, they will need to add a fan to cool the voltage regulator. In your case, a 12 volt supply should be acceptable.
Be sure to plug your 12 volt supply to the VBAT-GND terminal and not the DC recharge socket: the recharge circuit is only made for recharging a battery and can’t supply the currents necessary to run the motors at 12 volts.
Although the input signals will be analog, it will be converted to digital in the Arduino and then compared digitally. There would be a way of using a digital rotary dial instead of a analog rotary potentiometer, but without being able to replace the analog potentiometer in the linear actuator, this would make your project more complicated with no real gain.
If you do have long wires (dozens of feet or meters) for your rotary potentiometer, you could consider adding an additional analog-to-digital converter nearer to the pot, but I wouldn’t consider this unless you try the other method first notice significant problems with signal quality.
We hope this helps,
Hi,
The RB-Spa-783 motor controller would be powerful enough for that actuator, and actually has an embedded Arduino (168) microcontroller so the RB-Ard-34 and RB-Dfr-127 aren’t actually needed.
You should be able to connect the motor of the actuator to Mot_L, connect the potentiometer of the actuator to A0, connect your manual rotary potentiometer to A1, and then upload to the Arduino your new program that compares the manual potentiometer to the actuator’s potentiometer and then sends power to the motor to moves it in the appropriate direction.
Hope this helps,
Hi,
This board has an Arduino microcontroller which means that you can upload new programs to it directly with only a USB cable: this is one (of many) advantages of the Arduino bootloader. An Arduino programmer, such as RB-Dfr-127, is only needed if you want to update/change the bootloader itself, which wouldn’t be needed in your situation.
Another advantage of the Arduino platform is that you can take a second Arduino and program it to behave as an ISP programmer, and then you can reuse the second Arduino for other projects afterwards: you don’t really need a dedicated Arduino programmer!
As for the potentiometers, no, you don’t really need to match them. The way you wire each pot is as follows: for each pot, take one end of the internal resistor and connect it to ground, take the other end and connect it to your Vcc (5 volts), and then use the middle “wiper” pin as your signal connected to an analog input. If you do this with both potentiometers, no matter if they are 10k or 5k, you can still compare both analog inputs to find their difference since both pots are acting as voltage dividers over the same range: you’re just comparing ratios.
If you need more explanations on the last concept, let me know!