On my 1.5 M diameter theatre clock the balanced hands are driven by a stepper motor geared to the minute hand. A gearbox drives the hour hand at 12:1 ratio to the minute hand. An Arduino controls the clock via radio signals from another Arduino in a remote desk unit. The clock Arduino also switches relays to power 12 led light strips as 6 pairs of two. The clock gets hired out.
When disconnected from power young people tend to play with the hands. Moving the minute hand drives the stepper motor and I see leds light up on the relay boards used to switch the lights. My question is due to the high gearing of the minute hand to the stepper motor can rapidly turning the stepper motor create enough EMF to damage the controller?
That is a easy question if you can tell me what color shirt my neighbor's brother's wife is wearing. If you post an annotated schematic and links to the technical information on the hardware devices we can give you an accurate answer.
It is possible, as you say the stepper is acting as a generator and the gearing will not help.
The voltage generated could exceed the voltage ratings of the driver output devices.
Seriously, if you have not experienced a problem by this time, you likely do not have a problem. If really concerned, then make some measurements while you move the hands of the clock.
The stepper motor is possibly a YM2754 purchased as ROB-09238 from Core Electronics NSW and the controller was from Jaycar and I do not have the paperwork to identify it. It has four wires going to the Arduino. I suppose I am asking for a general indication if the motor is spun at speed could it generate EMF large enough to damage the controller.
I cannot answer that because I do not have circuit details. Post an annotated schematic showing how this is to be wired. The Arduino is NOT capable of driving it directly, you will need a controller. Be careful this is a highly inductive load.
Specifications:
• Rated voltage: 12VDC
• Rated current: 1.1A/phase
• Phases: 4
• Steps per revolution: 48
• Stepping angle: 7.5°
• Drive method: Unipolar chopper drive
• Resistance per winding: 20 ohms
• Starting frequency: 600pps (max)
• Holding torque: 700g/cm
This is the first time it is about to be hired out but I have other evidence it was played with after its first use. One reason I am checking it is the friction drive from motor to minute hand has failed and so moving the hands now does not turn the motor but when fix it by pin locking the minute hand gear to the spindle in future it will turn the motor. Thanks
How does this solve the electromechanical part? Get a new movement (whatever you are using for the movement - motor and controller) and find the problem later.
No the movement is fine 3D printed gears pressed onto concentric steel tube axels running in nylon bushes in a steel frame. But I think I got saved by the friction getting loose on the outer minute hand drive gear so kids moving the minute hand did not drive the stepper motor. Thanks to you guys I realize if the gear had been pin-locked to the tube the back EMF could have blown my circuits.
So I need to either keep the friction drive or draw the circuit so you guys can show me how to protect it when I pin lock the gear to the tube. Thanks so much really appreciate it..
The power supply was originally a 6 Amp plug pack but it died before the first performance on the technical shakedown rehearsal and was replaced with a 10 Amp plug pack. All went well after that.
