4QD's motor controllers all work from a variable voltage input so they are suitable for operation from radio control signals, PLC outputs or other automatic control system that can give them a 'demand speed' voltage input.
Most radio control systems use a pulse width position control signal. There is a separate page on the site explaining how that works. Since these radio control systems do not give a demand speed voltage, they cannot be directly connected to a 4QD motor controller. However we manufacture a range of microcontroller interfaces which translate directly this PWPM signal to suit our speed controllers.
An alternative (and perhaps the simplest) system is to use a standard radio control servo to operate a pot - this has the added advantage of giving a very good interference isolation barrier. See Interface Boards for Joysticks and Robots
Our controllers (except the 4QD series) are single ended; i.e. zero speed is zero voltage and full speed is perhaps 4v input (this will depend on the setting of the gain control). They have a separate input for direction. Most remote control applications require a joystick input for centre-zero operation. So 4QD have available a centre-zero 'Joystick' interface board for the VTX series and Pro-120 controllers. You can use the radio control's standard servo system to operate the pot on this, giving full speed and direction control.
See Joystick Interface boards
and Joystick Interface circuits
A suitable fuse in the battery line should blow before the MOSFETs. Our experiments show that a 25 amp blade fuse gives good protection to a VTX-40, VTX-40, Uni-4 or Porter 40. However, since fuses are extremely variable devices, it is not a guaranteed way of protecting!
The battery current is less than the motor current so a 25A fuse should easily carry the battery supply to a controller such as an VTX-40 where the motor current limit is around 55 amps. If the 25 amp fuse does, by chance, cause nuisance failure in the absence of any fault, increase it to 30 amps, or even more. However, the higher the fuse, the less the protection.
It is recommended that a 25 amp fuse be used for -35 controllers and a 40 amp for -70 models (it is less easy to get higher fuse ratings).
These are the fuse values fitted inside a boxed VTX controller.
It is quite easy to fit reverse polarity protection to any controller (or system) by means of a suitable single pole normally open relay. The circuit shows the method, which is 100% reliable so better than a fuse.
You only need one relay to protect the complete system as the relay is associated with the battery and not with a controller.
When the relay is off (open contacts), current flows through the 470R resistor to charge up the main capacitor(s) on the controller(s).
When the ignition switch is closed, the relay operates and shorts out the resistor, applying full power to the controller. Of course the main capacitor must have charged up adequately before you close the ignition: there must be enough voltage across the capacitor(s) to operate the relay coil!
If the battery is reversed, the MOSFETs within the controller(s) act as diodes, shorting out the + and - supply lines. With the circuit above there will then never be more than about 1.5 v present across the internal capacitor, so the relay coil cannot operate if the battery is reversed and the reverse current is restricted to a safe value by the resistor.
The value of the resistor can of course be altered to suit any application.
A suitable single pole automobile relay is available from several manufacturers: it is rated to handle 70 amps continuous, so for intermittent rating should be good for 120 amps or even more.
Reversing a permanent magnet motor is very simply: just exchange the two armature connections so the current is reversed! This can be done with a double-pole changeover (DPCO) switch or relay as shown, left.
Note that the motor is connected to the moving contacts (mnemonic: Motor - Moving), so that if there is a failure is the switch it is the motor that is most likely to get shorted out and not the controller!
Or you can use two single-pole changeover (SPCO) units - which will normally be two relays. One relay is operated for forward and the second for reverse.
The second diagram shows how it is done with two relays. These are shown both de-energised: note that both motor terminals are now shorted to the battery positive, shorting out the motor for maximum braking. Relay A changes to make the motor go one way, relay B for the other.
This same system is used with a series wound motor: the circuit is broken at the X point and the field inserted here. There is a page describing where this break should be made on the NCC and VTX controllers.
You should of course never reverse whilst the motor is running at any speed: not only will this cause a mechanical jolt but controller and motor could well be damaged. So you must turn the speed to zero, stop, reverse and turn the speed up again.
There is however a problem with commercial reversing controllers! If a driver threw a normal auto into reverse at 60 mph and junked the motor and gearbox - nobody would do anything other that blame the driver. But if a reversing controller failed because the driver reversed at speed - the controller manufacturer would surely be blamed!
So controller manufacturers have to put in extra circuitry to react sensibly when the reversing switch is operated at speed! The system used most commonly is the 'dual-ramp' reversing system. If the controller finds it is going the wrong way, it slows down to zero (under control of the deceleration ramp). When it gets to zero the relays are allowed to change. The controller is now going in the requested direction so the signal which caused it to stop is removed and the controller accelerates (under control of the accel ramp) to the requested demand speed.
To reverse at zero motor speed the controller either has to measure motor speed (as do the 4QD series controllers) or it has to know when it is safe to assume the motor is nearly stopped. This is what the VTX and Pro series do - they have regen braking and wind down the motor speed with full braking. So, when the internal demand speed gets to zero, the motor must be essentially stopped. Of course, with a heavy load, or downhill, the motor can be regenerating at this point, but the direction relays must be changed to cause the motor to stop on a hill, so there may be some relay arcing under these conditions. Nevertheless we have never seen a relay damaged by this!
This logic in the VTX and Pro of course would not work if the controllers did not include regenerative braking, therefore we do not supply them without this feature!
Of course this extra circuitry (essential to protect the manufacturer from customers who would otherwise abuse the controller) adds to the controller's complexity and therefore price. A reversing controller without this would obviously be easy - but then the manufacturer would have to test customers to make sure they were safe to use such a controller!
There is a road speed calculator available.
Given the motor RPM at full speed, the gear ratio (motor armature to final drive axle) and the wheel diameter it is quite easy to calculate your top speed.
If the motor rpm is 'S', the gear ratio is 'G' and the wheel diameter is 'D'
Then the final road speed (full speed) will be S divided by G multiplied by PI times D.
So for a motor of 3000 rpm, a gear ratio of 8:1 and a wheel diameter of 10" the final speed will be
Trouble is, since diameter is in inches and motor speed is per minute (revs/min) the speed we have calculated is inches/minute. Furlongs per fortnight might be as useful...
However there are 39.37 inches in a metre, so divide this by 39.37 to get metres. There are 60 seconds in a minute so divide by 60 to get metres/second. The answer we get is 5 metres/second.
300 x 10 x PI ------------- = 4.99 metres/second, 8 x 39.37 x 60
If you don't want to do the maths yourself, we have a JavaScript road speed calculator set up for you to use.
When one considers petrol fuelled road vehicles the shortcomings of electrical power soon become obvious. In a road vehicle there is a continual transfer and loss of energy between four areas:
Kinetic energy: the KE of a vehicle is ½Mv², where M is the mass (in kilogrammes) and v is the velocity (in Metres/second). This gives the KE in Joules
Potential Energy: the PE of the vehicle is M.g.h where M is the mass, as before, h is the height of the rise being considered and g is the 'acceleration due to gravity' - 9.8 for these calculations.
Windage: this is the power loss due to wind resistance. It is insignificant at slow speeds but it rises as the cube of the speed so it soon becomes the dominant factor.
Power input: from the engine. An over-simplification is that a certain amount of energy is supplied on each cycle of a piston, so the energy supplied is roughly proportional to the engine speed (rpm).
If all the above measures are done in Metres, kilograms and seconds the resulting energy is measured in Joules. Now one joule is one Watt x one second so it is easily converted into electrical power/energy.
In normal running on the flat at a constant speed the engine will feed power into the car and the windage will remove it. At any constant speed, on the flat, power from the engine is equal to the windage loss. If the vehicle comes to a hill it starts to loose speed, so the KE reduces (proportional to the square of the speed loss). As the vehicle climbs, it gains potential energy, proportional to the height climbed. So a relatively small speed loss (kinetic energy) can be transformed into a sizable height gain (potential energy). Coming down the hill, PE is once more converted back to KE (speed). Of course, during this manoeuvre the engine is still pumping in energy and windage is still causing loss. However a 1600cc car engine can readily give a power output of 70 kW and it can probably sustain this for 3 hours - an energy of over 200 kilowatt hours - on one tank full of petrol which takes, at most, 5 minutes to refill.
Now 70 kilowatts would be 5833 amps at 12v - an impractical current. Even at 96v it would be 729 amps, still excessive for modern batteries and motors. 300 amps at 48v (a much more manageable level of electrical power) is a mere 14.4 kilowatts. If 70 kW will drive the vehicle at 100mph against the windage then 15kW would drive the same vehicle at only 60mph. (100 divided by the cube root of the power ratio). Remember also that the petrol engine can give this 70kW for sustained periods but the electrical controller will get hot: most controllers available can give continuously only something like 1/3 of their short term output. 5kW would drive the same vehicle at only about 40mph.
Motor controllers cannot count! So they have no way of knowing how many motors they are driving: it's the total load (which is mostly mechanical, see our motor current calculator) that matters. So you can use several motors, by connecting the motors in series or in parallel.
For example, consider two 12v motors connected in series using a 24v battery with a controller that can supply up to 150 amps. The full output current of the controller is available to flow through both motors but the 24v maximum output will be shared so each motor will only see 12v (at up to 150 amps).
If the motors are parallel connected then each motor will see the full 24v (so speed will be doubled) but they will share the current. The motors will now have 24v at up to 75 amps each.
75 amps may be a reasonable peak current for many commercial motors, but 150 amps is going to cause 4 times (proportional to I2) as much heating and will likely destroy the brushes.
Incidentally, this series-parallel connection gives the possibility of a 'gear change', where the series arrangement will give high torque but slow speed and the parallel arrangement will give low torque and high speeds.
It is also possible to connect lots of small motors, for instance some garden railways use a collection of motors (4, 6 and 8 being common), perhaps 12v car fan motors, with a 24v battery.
The drawing shows four motors connected as two series pairs and 6 motors connected as three series pairs, the pairs all being in parallel.
Commercial servo systems are normally the third type and use motors designed for very fast response with a complicated control system so they tend to be expensive. However most systems do not need both speed and position accuracy so it is often possible to do a 'servo system' quite economically - if you know what you are doing and what you require.
For position servo systems some customers have used two of our 2QD controllers 'back to back'. One input is from the position control pot and the other from the feedback control. The motor connects between the two outputs. If the two pots are at the same point, both controllers give the same output, so there is no voltage across the motor.
It is also possible to use our 'joystick' board with an VTX controller for this purpose: the joystick board uses a 'bridge' configuration at its input, comparing the joystick position with a fixed reference. If the fixed reference is replaced by a feedback potentiometer a servo system results. The Joystick Interfaces page in our circuits section gives the circuit. Using this the standard pot would be operated by the steering wheel (or radio control system) and a feedback pot, operated by the position of the steering, would replace the potential divider R14 and R15. As the input voltage is varied, the steering motor will operate and the feedback pot will be altered so that the motor comes to rest when the two pots are in the same position.
Such a system is a melange of mechanical and electrical parts and neither can be fully defined without the other, so this is given as an idea only!
Such 'position servos' can be used for aerial rotators or for electrical steering systems. However the usual place that position servos are found is in radio control systems.
See Pulse Width Position Servo
For a speed 'servo' system you can use a tacho generator: this is discussed elsewhere in this sheet. Other references include a tacho feedback circuit.
In some applications (e.g. 'double heading' a miniature train) it may be necessary to use two controllers, each driving separate motors, driven off the same control pot.
The VTX and Pro series controllers can be supplied with an optional expansion connector for this purpose. When two controllers are linked via this expansion controller, one will be a slave to the other: if only the master's ignition is switched on the slave will also be activated and its speed and direction will be controllers by the master and both will be controlled by the master's acceleration and deceleration ramps.
You should order the expansion connector, (XCN-006D or XCP-009D) to be fitted when ordering the controllers as it is an optional extra. Details of the connection for double heading are included in the instruction manuals.
Be warned that the design of the Pro and VTX changed. It is not a good idea to mix a Mk 1 with a Mk 2 in a double heading system as the circuits and responses are slightly different and they cannot be guaranteed to work together.
For the 4QD series (or any other controller) it is necessary to set the gain, acceleration and deceleration ramps on each controller as close to each other as possible, though usually exact accuracy is not very important. They can then be fed from the same pot: this will be powered from the master and the voltage on the moving contact fed to the slave. The slave must have a 10K resistor fitted to over-ride the pot fault detection.
Ignition lines and reverse lines for both controllers are simply joined and fed off the master controls.
If the controllers are not well matched, one motor will work harder than the other, so it will get hotter: this is a good way of testing whether the controllers are sufficiently well matched.
With a digital controller, such as the Pro-150 setting up ramps and gain to be identical on the two controllers is very easy as this is done by programming. So with these all that is required is to feed one set of controls (speed pot, reverse switch and ignition) to both controllers on a Y lead configuration.
Details of fitting the expansion connector for VTX and Pro series are in the service area
Some people think that all they really require is a soft starting device, to allow the motor to ramp up to speed at a controlled rate. Such devices do indeed exist on mains controlled motors.
However for low voltage use, all modern systems use high frequency MOSFET choppers - these operate at 20kHz. If a device is going to control the speed for, perhaps, 2 seconds, during starting, it is a motor speed controller. If you are working at 20kHz, then 2 seconds is some 40,000 cycles - an eternity to the controller. If you have a motor speed controller in circuit, you may as well use it - a device to soft start and then drop out of circuit would actually be more complicated than a simple motor speed controller!
A motor which is heavily loaded will always run slower than an unloaded motor. This statement seems so obvious that it is hardly worth saying - yet there are motors (stepper motors and synchronous motors) where it is not true and speed is independent of load. However, for normal d.c. motors it most certainly is true.
Consider a motor whose rating plate states 2000 rpm, 20 amps and 24v. This means that the motor will run at 2000rpm when working from 24v and when loaded such that it is drawing 20 amps. Moreover the 20 amps quoted on the name plate will normally be the continuous 'safe working current' - in other words if you run the motor continuously at more current than this then it may eventually get too hot.
But such a motor may take, perhaps 120 amps if you stall it. Knowing V, the motor voltage (24v), and I, the stall current, we can, by Ohm's law work out the armature resistance, V/I. So our stall current shows that the armature resistance is 0.3 ohms. We can now draw a graph:
This shows that the expected no-load speed is nearly 2600 rpm and that, at 50 amps, the motor will run at about 1000 rpm. Note however that the name plate working point (NP) is quite near the top of the curve and a properly loaded motor won't use three quarters of the curve.
It should be evident from this that a larger motor, with a higher stall current, will have a flatter slope and therefore better speed stability. The rule is - the larger the motor, the better the stability against load variations. You would also expect a slower motor to have a flatter slope, except that a slower motor (of the same size) will be wound with more turns of thinner wire, so its stall current will be less.
This graph is for a motor operated from a fixed supply voltage. A motor speed controller reduces the available voltage to reduce the speed, shown by the pecked lines parallel to the main graph. So reducing the top speed with a simple controller also reduces the available stall torque.
It is evident from this that, if your gear ratio is such that you never operate the motor above half speed, then you are losing a lot of maximum torque and performance. It also follows that, if you start a motor under heavy load, you have to put a large voltage across it before it moves. Then, if the load suddenly reduces, the motor will suddenly spring to life at high speed.
In most battery applications the operator automatically adjusts the controller's output voltage (the motor speed) to compensate for load variations so there is no problem. The times when this is not true are either when the speed is not operator controlled and the load is varying or when there is a sudden change in load such that the operator finds it difficult to react fast enough and the vehicle surges when the load reduces suddenly (this is a situation which occurs frequently in Robot Wars). In these cases some form of closed loop control may be required.
Closed loop means that the motor speed is measured and fed back to the controller which adjusts itself automatically to keep the motor speed more or less constant. There are many ways of doing this which vary in complexity and expense and are more or less effective.
A tacho generator is, essentially, a small p.m. motor which is driven as a generator and which gives an output voltage which is accurately calibrated to be a defined measure of the rotation speed. 'Accurate' implies expensive. However in most applications high accuracy is not actually required so you can use a small motor as a generator. Any calibration and scaling can be done in the electronic circuitry. A suitable circuit is available as an accessory board for the Pro-120 and VTX series but can be used with other controllers from 4QD's range.
The tacho generator's output is fed to an 'error amplifier' which also has as its second input the 'demand speed' signal (basically the signal from the speed control pot). It compares the two and gives an output which is dependent on the difference between the two input signals, i.e on the error between them. The tacho generator is measuring the actual motor output speed. If this is less than the demand speed the error amplifier adjusts the input to the motor speed controller to speed the motor up. The motor speed controller, if the load is sufficient to warrant it, can them give its full output voltage to drive the motor so that full stall current could, in theory, be available if required. It sounds like a large improvement and indeed it is, but at a potentially large cost: the tacho generator can add a lot to the cost the error amplifier adds to the cost of the electronics. However, these costs need not be large. More details are given in our circuits archives.
A tacho generator gives a polarised output voltage: positive voltage for one direction and negative for reverse direction so the error amplifier has to be able to cope with either polarity if the controller is to reverses the motor.
See our circuits archives for the circuit of a suitable error amplifier to compare tacho feedback voltage with the demand speed.
One limit on this method is that the motor shaft may not have a suitable gear to be sensed. Also the motor drive gear is usually small, with few teeth. If the motor's full speed is 1850 rpm and we have, say, 8 teeth to count then there will be 1850 x 8 pulses per minute, or 250 pulses per second. If we want a speed range of 25:1 then there will only be 10 pulses per second at slow speeds, so there is 1/10 second between pulses. It is not then easy to get the motor speed to respond quicker than 1/10 second. or it will wander at slow speeds. The output of the FVC must be steady to avoid motor hunting. This limits the slow speed performance of the system when used with an analogue frequency to voltage converter.
For this reason pulse tachos (as these are sometimes called) are more suitable for use with microcontrollers which can adapt their response to the expected motor speed, hence to the time between pulses.
4QD's controllers don't currently use IR compensation for the above reason. Moreover, in most battery vehicle applications, the operator automatically compensates for load variation by using the throttle device to increase/decrease speed as he requires so closed loop control is totally unnecessary. Only the 4QD series are closed loop and these do sense armature voltage but do not employ IR compensation. However it is quite easy to feed a tacho generator into them to properly close the loop.
We also have a tacho error amplifier available for Pro 120 and VTX series, this could be used with our other motor speed controllers.
Whilst it is true than a motor, connected straight to a battery with no controller, draws a large surge current when connected up, this does not happen when the motor is connected to a motor speed controller.
The surge is caused because the motor, when it is turning, acts as a generator. The generated voltage is directly proportional to the speed of the motor. The current through the motor is controlled by the difference between the battery voltage and the motor's generated voltage (otherwise called back EMF). When the motor is first connected up to the battery (with no motor speed controller) there is no back EMF. So the current is controlled only by the battery voltage, motor resistance (and inductance) and the battery leads. Without any back emf the motor, before it starts to turn, therefore draws the large surge current.
When a motor speed controller is used, it varies the voltage fed to the motor. Initially, at zero speed, the controller will feed no voltage to the motor, so no current flows. As the motor speed controller's output voltage increases, the motor will start to turn. At first the voltage fed to the motor is small, so the current is also small, and as the motor speed controller's voltage rises, so too does the motor's back EMF. The result is that the initial current surge is removed, acceleration is smooth and fully under control. Ever if the motor speed controller's input is increased very suddenly it has a built in time constant which winds the output up slowly, so still there is no excessive surge and acceleration is smooth.
Many older controllers used a low switching frequency, even as low as 50hZ. This causes three problems: firstly you get a whine or hum from the motor, especially at slow speed. Secondly and more seriously, the lower the frequency the less efficient the operation, so the motor gets hotter and the battery life is not as good as with modern controllers operating at 20kHz or so. The third problem is the most serious: take a motor with a d.c. resistance of 1.2 ohms: in stall, this motor (from 12v) would draw 10 amps. It can never draw more than this stall current. Even if the low frequency controller were rated at 1000 amps, this would not help.
Now, if the motor is running at 10% full speed, the controller is switching the battery on for 10% of the time and off for 90%. During the 'on' time the motor can only draw 10 amps, never more. During the off time, the current decays to zero. Therefore the average current drain is only slightly over 1 amp absolute maximum at this speed. The motor therefore has no power at low speeds.
With 20kHz switching frequency, the motor current is essentially constant as the motor's inductance keeps the current flowing throughout the controller's 'off' time and the motor current varies only by 1 or 2 %. Therefore these high frequency controllers can drive nearly the full 10 amps into this motor, at any speed. Therefore a high frequency controller gives far better pull at slow speeds.
The lower switching frequencies are better with smaller, higher voltage motors where the motor has a much larger inductance. However high current, low voltage motors have a very low inductance so a high switching frequency is necessary for best performance.
See also our circuits archive for technical information on pwm, including circuits.
Many people try to use a tooted belt as a reduction gear from a motor to a drive wheel. This is fine - as long as you do not expect to get regenerative braking through the belt!
The motor shaft will always rotates a lot faster than the drive wheel, so there is a fairly large reduction ratio via the belt. This involves a pinion on the motor with a small diameter and few teeth, with a larger pinion on the driven wheel. Regen braking requires feeding power in reverse through the belt with the large wheel driving the small one.
It is fairly well known in engineering circles that, if you try and feed power via a toothed belt from a large wheel to a small one, you must expect belt slippage. Clearly this is not acceptable with a toothed belt!
Consider the top diagram, left. A is the motor (drive) pinion, B the driven gear. B is under tension and is transferring power. Side C is slack and where C touches the large wheel there is no tension on the gear teeth. Belt tension (pressure on the gear teeth) increases as the belt travels to side D.
Now consider B driving and A driven. Side D will be slack, side C in tension and the teeth at side D will have no tension on them. The problem is that only very few teeth are in contact with the belt. If an A has 8 teeth, then it is pretty clear that only about 3 teeth will be able to do anything!
In the second diagram a third wheel is present as a pressure roller to try and maintain contact. Clearly the situation is better but, with our 8 tooth wheel we still only have probably 5 teeth doing anything. With carefully maintained alignment you might just be able to get away with this - but it certainly cannot be recommended.
So with a toothed belt, expect to have to forgo the benefits of regenerative braking. Even when controlling the regen braking by hand, it's very difficult to know how much braking you can apply and no automated system could possibly compensate for wear in the mechanics and for belt stretch.
Torque is not really a controller function, but it is directly related to the current flowing in the motor. The mechanical torque is proportional to the motor current and the relationship is defined by the motor's design, so read the motor specification sheets!
However, motor torque is not the output torque at the wheel. The final drive torque is the motor torque multiplied by the drive gear ratio. But the final speed is the motor speed divided by the drive gear ratio. So it follows that if you increase speed - you reduce final drive torque and vice versa. For your machine, you need to arrive at the correct compromise.
We have emphasised drive gear ratio. This is not the same as the gear ratio you have but also includes the diameter of the road wheels. Imagine a motor rotating at 3000 r.p.m. with a gearbox ratio of 10:1. The output speed of the gearbox will naturally be 300 r.p.m. This is the shaft that is rotating the wheels. So the wheels will rotate at 300 rpm. So the machine will move at 300 times the wheel circumference per minute. Final drive gear ratio is therefore directly affected by the wheel diameter.
If you have too much torque - then when you meet resistance (such as another robot) something has to give. It is going to be traction which is list: you (or the other robot) will slip. So the torque you need is entirely down to how well your robot grips the ground. No point in having immense torque if your wheels slip!
If your torque is too low, then in a head-to-head shove, you will loose. But low torque implies high speed. High speed does two things: it makes your robot more difficult to steer, but it also means that the kinetic energy in your robot is high. So it you are going to employ high speed collision techniques, you need speed, not torque.
The art of making a successful machine is in getting the trade off correct!
It is very dangerous to tow any electric vehicle. If any E.V. is to be towed, you must disconnect the motors or else jack the machine so that the drive wheels cannot turn.
If the controller is one that short-circuits the motor when at zero speed, then towing will cause the motor to generate into the short. The motor will generate a lot of current. Not only will that work like towing with the hand brake on, but also the generated current will burn out the relays of the controller and it may also damage the vehicle's electric motor.
This excessive back emf will flow through the controllers MOSFETs (through the integral, reversed body diode) to recharge the battery. However since it is flowing backwards - the MOSFETs cannot interrupt it and the controller cannot control the current. So it is likely to rise to an excessive level and destroy the controller.
Disconnecting the battery won't help. Since the back emf generated by the motor is larger than the normal battery voltage it is likely to be higher than the controller can handle and the controller will simply fail!
A voltage follower takes an input voltage, say 0-3 v, and gives an output voltage, e.g. 0-24v, such that the output voltage is controlled by the input.
This is exactly what all controllers made by 4QD do, so any of them may be used as voltage followers.
Input voltage range for most controllers is 0-3v, with 0.5v (or less) corresponding to zero speed and 3v giving full speed. The zero speed at 0.5v is required so that the parking brake release and reversing etc can be done below this level.
On models that have a gain control (most), the full speed voltage can be adjusted - the zero speed also gets adjusted pro-rata.
Where pot fault detection is fitted, this needs to be disabled. See Digital control for more information.
All controllers have a filter at the input and this will average out an input, so it is quite permissible to feed in a pwm signal and let the controller respond to the average of the pwm signal.
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