Posted October 2, 20159 yr I am wonder if this had been done. I want be able to vary the turning radius using a servo but I don't have a train remote
October 2, 20159 yr I am wonder if this had been done. I want be able to vary the turning radius using a servo but I don't have a train remote One important think to remember is that the train remote does not offer true proportional steering anyway. When you turn the wheel on remote it sends a series of "increase"/"decrease" commands and each causes the servo to turn one "step". So the angle of the servo does not depend directly on the posion of the wheel, but on the number of command it receives. The red button sends "return to neutral" command. The regular PF remote sends "incease to max" and "decrease to min" commands, which are not available from train remote.
October 2, 20159 yr Author Do u guys understand what I want to do with my servo?? I want to be able to control the turning radius using a servo so that I have that true return to center
October 2, 20159 yr Are you looking for proportional steering control? Use the IR speed control commands to set to one of 7 steering angles right and one of 7 left plus return to center?
October 2, 20159 yr For a LEGO solution you'll need a train remote or a rechargeable battery. Or an RCX programmed to speak the Power Functions protocol over its IR port. There are also non-LEGO solutions too. Arduino has been mentioned, but presumably there are others. Heck, even a universal remote control would probably work.
October 3, 20159 yr For a LEGO solution you'll need a train remote or a rechargeable battery. Or an RCX programmed to speak the Power Functions protocol over its IR port. There are also non-LEGO solutions too. Arduino has been mentioned, but presumably there are others. Heck, even a universal remote control would probably work. I think you can also use NXT with the NXT IRLink Sensor. Arduino with an IR LED is probably the cheapest of the bunch to implement.
October 3, 20159 yr Private Message, not Pulse Modulation. I was not referring to that I just wanted to say you can control the positions of the servo motor useing the 9v speed regulator
October 3, 20159 yr I was not referring to that I just wanted to say you can control the positions of the servo motor useing the 9v speed regulator Perhaps he could also mount it on a trailer behind the vehicle and chase after it to control it.
October 3, 20159 yr I was not referring to that I just wanted to say you can control the positions of the servo motor useing the 9v speed regulator Really? That would surprise me. It would mean that I didn't understand how either or both of the PF variable speed system or the speed regulator worked. As I understand it, the speed regulator works by varying the voltage supplied to the motor, whereas the power functions system uses coded messages to tell the motor how fast (or in the case of the servo motor, how far around) to go, all at the full 9 volts. I don't see how using the speed regulator can help here.
October 3, 20159 yr Really? That would surprise me. It would mean that I didn't understand how either or both of the PF variable speed system or the speed regulator worked. As I understand it, the speed regulator works by varying the voltage supplied to the motor, whereas the power functions system uses coded messages to tell the motor how fast (or in the case of the servo motor, how far around) to go, all at the full 9 volts. I don't see how using the speed regulator can help here. Coded messages are sent to the IR receiver which in turn controls the servo by varying the voltage delivered to it.
October 3, 20159 yr Really? That would surprise me. It would mean that I didn't understand how either or both of the PF variable speed system or the speed regulator worked. As I understand it, the speed regulator works by varying the voltage supplied to the motor, whereas the power functions system uses coded messages to tell the motor how fast (or in the case of the servo motor, how far around) to go, all at the full 9 volts. I don't see how using the speed regulator can help here. I thought you would have known that the speed regulator controls the voltage of the output and I think the servo motor runs of the voltage power level of the output. In other words as you increase the voltage the servo should go through each step until it reaches 9v max.
October 3, 20159 yr Coded messages are sent to the IR receiver which in turn controls the servo by varying the voltage delivered to it. That seems plausible. You learn something new every day!
October 3, 20159 yr The LEGO servo motor works by the duty cycle of the signal sent on the C1 and C2 connections, provided that the 9V and 0V connections have sufficient voltage to operate the motor and its internal circuit. The position depends on the proportion of the supply voltage set by the duty cycle, not on the absolute voltage. Whilst a traditional servo has continuous position based on duty cycle with an analogue feedback control, the LEGO servo motor has positions 0-7 in each direction set by the fixed duty cycle levels from the alpha chip in the IR Receiver or LiPo battery with a digital feedback control. A wiper on a circuit board inside the servo motor makes contact corresponding to the position and this is compared with the input duty cycle to determine whether the motor needs to move. I think if a variable duty cycle independent of the supply voltage were applied to C1 and C2 then the servo motor would respond when the duty cycle reached each threshold. More voltage than the supply voltage could hurt the servo motor. Whether it has enough intelligence to avoid trying to exceed its end-stops is something I have not tested. When used as it is meant to be used, this would not occur because the signal input would be a proportion of the supply. Certainly supplying more + or - codes by IR is trapped by the alpha chip in the IR Receiver so that the applied duty cycle would not exceed the supply voltage. I have used an NXT and IR Link sensor to operate two servo motors from a PF IR Receiver. The NXT can put out any of the PF codes so it can do + and - codes but also absolute speed/position codes. I used the absolute codes in a sequence that moved by 1 position at a time and also 2 positions at a time, as a servo test routine. I have also set the absolute speed of a train using codes from the NXT. Mark
October 3, 20159 yr The LEGO servo motor works by the duty cycle of the signal sent on the C1 and C2 connections, provided that the 9V and 0V connections have sufficient voltage to operate the motor and its internal circuit. The position depends on the proportion of the supply voltage set by the duty cycle, not on the absolute voltage. Whilst a traditional servo has continuous position based on duty cycle with an analogue feedback control, the LEGO servo motor has positions 0-7 in each direction set by the fixed duty cycle levels from the alpha chip in the IR Receiver or LiPo battery with a digital feedback control. A wiper on a circuit board inside the servo motor makes contact corresponding to the position and this is compared with the input duty cycle to determine whether the motor needs to move. I think if a variable duty cycle independent of the supply voltage were applied to C1 and C2 then the servo motor would respond when the duty cycle reached each threshold. More voltage than the supply voltage could hurt the servo motor. Whether it has enough intelligence to avoid trying to exceed its end-stops is something I have not tested. When used as it is meant to be used, this would not occur because the signal input would be a proportion of the supply. Certainly supplying more + or - codes by IR is trapped by the alpha chip in the IR Receiver so that the applied duty cycle would not exceed the supply voltage. I have used an NXT and IR Link sensor to operate two servo motors from a PF IR Receiver. The NXT can put out any of the PF codes so it can do + and - codes but also absolute speed/position codes. I used the absolute codes in a sequence that moved by 1 position at a time and also 2 positions at a time, as a servo test routine. I have also set the absolute speed of a train using codes from the NXT. Mark Oh so that is how it works, may I ask did you work for Lego in designing the power functions system?
November 11, 20159 yr Having recently taken delivery of a 9V speed regulator and a PF servo motor, I can now confirm that the speed regulator won't make the servo turn.
November 11, 20159 yr What do you mean by 9v speed regulator? The old 9v train controller used for metal tracks (with the big yellow dial) will not work with the servo motor. The newer pf lipo battery will (by turning it on and turning the orange axle hole) and I assume the newer 6AAA battery box found in the newer train sets will work the same way as well. The newer train remote control (with the 2 orange dials) will control up to 2 servos when the servos are plugged into an IR receiver which is powered by a battery box. Edited November 11, 20159 yr by allanp
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