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RC (Remote Control) Support Page
We get this question all the time, so here's a webpage to help with this topic. How do I use a RC controller to drive a motor?
RC BasicsThe RC transmitter outputs the signal; the receiver receives the signal and then commands the servo to do its stuff. RC systems have from 2 to 8+ channels (i.e. a 4 channel radio can control 4 servos). RC receiver outputs are simply a 1.5ms pulse about every 20ms. They are intended to control servos remotely. The 1.5ms pulse is varied from ~1.0ms to ~2.0ms to give the full range of travel. The 20ms can vary some, but if it’s too long between pulses the servos will become sluggish, the closer together the higher torque output. Most people want to control more than just servos, so this page is intended to help. Below are some images of a servo pulse.
ServosServos are DC motors with built in gearing and feedback control loop circuitry. And no motor drivers required!
Servos are extremely popular with robot, RC plane, and RC boat builders. Most servo motors can rotate about 90 to 180 degrees. Some rotate through a full 360 degrees or more. However, servos are unable to continually rotate, meaning they can't be used for driving wheels (unless modified), but their precision positioning makes them ideal for robot arms and legs, rack and pinion steering, and sensor scanners to name a few. Since servos are fully self contained, the velocity and angle control loops are very easy to implement, while prices remain very affordable. To use a servo, simply connect the black wire to ground, the red to a 4.8-6V source, and the yellow/white wire to a signal generator (such as from your microcontroller). Vary the square wave pulse width from 1-2ms and your servo is now position/velocity controlled. All servos have three wires:
Servos can operate under a range of voltages. Typical operation is from 4.8V to 6V. There are a few micro sized servos that can operate at less, and now a few Hitec servos that operate at much more. The reason for this standard range is because most microcontrollers and RC receivers operate near this voltage. So what voltage should you operate at? Well, unless you have a battery voltage/current/power limitation, you should operate at 6V. This is simply because DC motors have higher torque at higher voltages.
So how do you apply this square wave to your servo? If your robot is remote controlled, your RC receiver will apply the proper square wave for you. If however your robot is running from a microcontroller, you must:
Servo current operates the same as in a DC motor, except that you now also have a hard to predict feedback control system to contend with. If your DC motor is not at the specified angle, it will suddenly draw large amounts of current to reach that angle.
Driving DC Motors or Other Loads from a RC SignalYou can go a few ways to control loads such as motors from an RC controller. Below are some methods
Method 1: You can use this RC switch to turn a load on and off. You will not be able to remotely control the direction. This is ideal for turning a light on and off or turning a motor on and off that only operates in one direction. The Relay acts like a switch, so any voltage (up to 240VAC) can be used. The contact are rated for 10Amps. The relay is triggered by a onboard microcontroller that monitors the pulse width of the receiver channel.
Method 2: You can just use this RC switch to drive a motor fwd/off/and reverse if you don't need speed control. The RC switch has limit switch inputs to limit motion in either or both directions. The relay acts like a switch, so any voltage (up to 240VAC) can be used. The relay contacts are rated for 8 Amps. The relay is triggered by a onboard microcontroller that monitors the pulse width of the receiver channel. When the stick is pushed one direction, just the single pole relay comes on driving the load forward, then the stick is pushed the other direction, both the single pole and double pole relay are pulled in turning the load on and reversing it.
Method 3: If you want speed control on your motor, you can use a Pulse Width Modulation (PWM) motor controller with o
The RC board has an onboard microcontroller which reads the incoming RC signal and outputs a PWM signal to drive a PWM motor controller. The image on the left shows the PWM output compared to RC input for one channel. Our RC interface board reads two RC channels and gives you 2 PWM outputs. The RC controller PWM output can be set on as two independent controls or the channels can be mixed. In addition to the PWM output, each PWM has a direction bit so when the stick is in reverse the direction bit is high, when the stick is pushed forward the direction bit is low. The board also contains a single pole relay for turning a load on and off (as in method 1). It also contains a single pole and double pole relay so you can turn a load on and off and reverse it (as in method 2).
The controller on the RC board has also been programmed to filter and dismiss most erratic or lost readings.
The PWM signals that are output from the RC board are only TTL levels (5V Transistor Transistor Logic). To drive a motor or other load you need to take the PWM TTL signal and amplify it. Our PWMs are rated for 3Amps and operate in 12-55VDC, which is good for the IG32 or IG42 motors. The PWMs can be run in parallel, i.e. 2 PWMS motor controllers driven off of one PWM output. i.e. with our ATR kits, we run two PWM to the left 2 motors (one per motor) and then two PWMs to the right motors when using the larger IG42 motors.
Method 4: You can use an integrated MD22 or MD03 motor controller that has an RC mode. The MD22 is a dual channel (2 motor) controller. The MD03 is a heavy duty single motor controller. These controllers’ works fine, but does not have filtering and buffering making it a little more susceptible to noise and missed radio signals. The MD22 and MD03 require 5V, you can pull this from the receiver, but if the voltage falls much below 5V, things start getting a little squirrelly. If you are using a standard receiver NiCad pack, you will only get about 4.8V, which will work, but is borderline. We recommend using a 7.2 or 9.6V battery pack and then use a 5V regulator to power the receiver and MD22 or MD03.
Method 5: You can use an integrated SaberTooth 2x10 or SaberTooth 2x25 motor controller. Both motor controllers have an RC mode. Both Motor controllers are dual channel, so they can be used to mix you radio signals for single stick skid steering or they can operate independently. These controllers’ works fine, but they do not have filtering and buffering making it a little more susceptible to noise and missed radio signals. They do utilize an running average and will reject out of range signals. These controllers also supply 5V to drive your receiver. The 5V supply is not powerful, so it should only be used for the receiver with no additional loads such as servos plugged into the receiver (you will want to use a separate 5V supply if you want to add servos to the other channels of the receiver. We also carry the Syren 10 and 25 motor controllers for those who only want to drive one motor and save a little money from the dual motor controllers.
We have also had a custom Sabertooth 2x10 built specifically for the Spektrum RC systems. With the new Spektrum RC systems we found some minor issues using them. The RC signal was not as high a range for ms output and the receiver needs a little more power than 72/75 MHz radios. It is also common to add a couple servos to the receiver and the standard Sabertooth RC does not have a large enough regulator for that. So we have had these custom Sabertooths made with larger 5V switching supplies and reprogrammed to work with spektrum RC systems (they will still work great with other RC systems too). This custom RC Sabertooth also has the larger heat sink than the standard RC Sabertooth. Click here for a schematic of hooking up the custom Sabertooth with a Spektrum RC Radio.
Motor Hookup: In all cases, you want to hook up your motors properly using our electric motor hookup kit.
RC Controllers: RC controllers can be found on the link below. All of the above will work with any RC controller. PCM radios like the Optic6 and Eclipse7 have better range and reliability since these are digital radios and can be programmed with fail safes.
We also carry the Spektrum Radios which we have had outstanding results with. With the spread Spektrum frequency hopping DSM2™ technology we get great range and reliability regardless of the other 2.4GHz systems around like routers and phones. The other benefit of 2.4GHz is most motor noise and mechanical noise/interference is well below this frequency which often causes issues with the 72 and 75MHz radio systems.
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