Electromechanical porn - Page 1
Forum section: electronics / general

author: Psi
author_rank: Super Contributor
timestamp: May 21, 2012, 08:44:46 am
content: That really is a beautiful piece of engineering.

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: May 21, 2012, 08:48:08 am
content: Quote from: Psi on May 21, 2012, 08:44:46 amYes. And thanks Mike for posting this.

author: typeglob
author_rank: Contributor
timestamp: May 21, 2012, 10:23:25 am
content: I enjoyed watching that, thanks.

author: firewalker
author_rank: Super Contributor
timestamp: May 21, 2012, 11:06:01 am
content: Nice one! I love electromechanical gear.I don't believe that driving the gyro with full voltage specs will have a significant impact. Those type of motors are mostly frequency depended. Also the "OFF" sign moved. I am guessing that the designer would have predicted low voltage situations and wouldn't let the "OFF" sign to go away if there was an issue.Alexander.

author: mAJORD
author_rank: Contributor
timestamp: May 21, 2012, 12:33:22 pm
content: Fast erection indeed!Never seen inside one of these (or any oldschool attitude indicator), amazing , much more complex than I thought they would be.

author: EEVblog
author_rank: Unknown
timestamp: May 21, 2012, 12:34:48 pm
content: I was also surprised at the complexity of it all.A heck of a lot of engineering went into that. Not just the operation, but the packaging too.Dave.

author: free_electron
author_rank: Super Contributor
timestamp: May 21, 2012, 02:59:47 pm
content: Now, as a comparison we need a teardown of a modern MEMS based gyroscope

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: May 21, 2012, 04:30:52 pm
content: One of these pretty cheapon Ebay UK at the moment- several other similar ones from same seller.

author: SeanB
author_rank: Super Contributor
timestamp: May 21, 2012, 06:13:18 pm
content: Voltage would be 115VAC 3 phase 400Hz, or 28VDC. I changed way too many of these in my time. The nicest are the engine P2 vacuum operated ones, as they are so simple to describe and use. Looked this week and saw I still have the training manual about them.This would have most likely been a standby unit, as normally the gyro is a integrated unit driving an attitude indicator ( or nowadays a crt in a glass cockpit) and would be mounted at the mass centre of the aircraft.Edit: Looking at that Ebay store...... I want the MB seat. I can ask Gav as how to keep it safe, he was trained on them...... Me, I did NWS.

author: pickle9000
author_rank: Super Contributor
timestamp: May 21, 2012, 06:35:20 pm
content: Wow, I once had an opportunity to work on an old Fairmont Tamper (machine that aligned railway tracks). I never got to look inside the gyro (a sealed unit but similar size and did run off 115 supply), very cool.The machine was from the late 60's early 70's. It was pre computer so used chart tables. To align the new railway track you first run the track. That is run the machine down a section (say 100 meters), it recorded track position using shadowboards (for curve / straightness), encoders on the wheels for distance and the gyro for supers. The 2 chart tables where rotary and the rotational location was distance. Once table recorded curvature (from the shadowboard system) the other was the super or superelevation (how far tipped over left or right). Once track position was recorded on the chart you used 1/16 black fabric tape (like the kind used for pcb work) to correct the line to the position you would like it. Yup you put tape on the chart paper. You then place an optical reader on the recorder and use the recorder to control the machine. It followed the tape lines and moved the machine accordingly.A tamper is a violent machine that used vibrators grabbing onto the machine to move the track. It moves about a half meter grabs the track, vibrates and places then repeat. Yes tubes where involved in places.New tampers (now HTT) machines still a shadowboard system virtually identical to the original.Totally enjoyed that, thank you mike.

author: sonicj
author_rank: Frequent Contributor
timestamp: May 21, 2012, 11:05:09 pm
content: I've got this one:http://www.mcico.com/4300-6980-L-CNA52187DD1B5C.html?MN=!MN!I bought it to hack up and install in my simulator, but I can't bring myself to destroy it. Its just too nice of a piece of equipment...-sj

author: mAJORD
author_rank: Contributor
timestamp: May 21, 2012, 11:26:02 pm
content: Not sure about those really old machines, but the current (and 80s onward) ones use a simple Pendulum system connected to a potentiometer for superelevation, but yeah, on the HTT machines at least, they still use shadowboards, though with a laser/reciever system to automate.I'm only familiar with the Austrian Plasser Tampers. The older units (not that old though surprisingly) have an interesting mix of analogue electronics meets machinery. They used nothing but opamps, + analogue multiplers and dividers to calculate track correcton. This translates to a rack full of cards, packed full of opamps and through hole resistors. Fun. (especially when someone wants one fixed)Quote from: pickle9000 on May 21, 2012, 06:35:20 pm

author: pickle9000
author_rank: Super Contributor
timestamp: May 22, 2012, 12:15:49 am
content: I think we have 2 Plassers in all of Canada Not sure about the vintage but it's like walking onto the Seaview from "Voyage to the Bottom of the Sea". Banks or flashing lights, amazing machine so much more refined than the Fairmont stuff.You are so right the new ones all use a pendulum, as soon as real computers went in. The first ones had angle iron bolted to a metal desktop case 286. Floppy drives, power supply and all, no hard drives they couldn't stand the vibration. It's amazing what you can get away with. There is still one of these unit's (286 computer driven) working for a small railway that I know of....mike

author: westfw
author_rank: Super Contributor
timestamp: May 22, 2012, 05:57:57 am
content: Huh. I've been wondering whether (cheap) audio amplifier chips could be used as motor drivers (especially for disk/cd spindle motors); looks like it might be a reasonable idea.

author: amyk
author_rank: Super Contributor
timestamp: May 22, 2012, 08:34:18 am
content: Quote from: sonicj on May 21, 2012, 11:05:09 pmAnd expensive... $4,029.00

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: May 22, 2012, 09:32:43 am
content: Quote from: amyk on May 22, 2012, 08:34:18 amPay me half that and I'll tell you which way's up any time of the day.

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 22, 2012, 01:51:17 pm
content: It's possible to get 3 phase using only two channels. Look up "open delta".The newer digital audio amplifiers are switching power supplies and will drive almost anything as long as their output current rating isn't exceeded, but many of them are BTL so you'll need transformers.

author: free_electron
author_rank: Super Contributor
timestamp: May 22, 2012, 02:43:55 pm
content: Quote from: westfw on May 22, 2012, 05:57:57 amyou may get it to spin but you are going to ruin it very quickly ..Driving a harddisk motor is pretty complex.The motor is 3 phase in star configuration. Only 2 wires are activated at a time and the third is used to monitor the midpoint to detect when the magnet has transitioned from one winding to another. There is no hall feedback ,Driving is done using 3 half bridges in pwm mode under control of a processor ( not a generic CPU or microcontroller but a custom processor built for this job )The drive current is NOT a sinewave .. the top folds back. The reason is the mechanical construction of the motor. driving it with sinewaves causes acoustical noise and vibration. it is sufficient to get the coil current close to the crest of the sinewave, then let it die out ( the inertion of the mechanical mass in the platters makes it 'coast' to the other winding , where it is 'caught' and guided along.this reduces the amount of electrical power required as well. plus it makes the drive run very smooth.There is lots of other trickery involved. A harddisk has a technique akin to 'launch control' on cars. At power up a small current is sent trough the voltage is applied to the winding and we shut down the driver at a preset current limit. by measuring the time to get to the preset current we can find out where the rotor sits.. so we know how the first commutation needs to be done. ( can't have the motor start backwards ! if the heads would be on the platters it would be game over ... )the processor then goes into launch mode and starts driving the motor with a crude pattern that sweeps up in speed. once we get enough back-emf from the coils ( at about 100rpm ) it goes into loop-control . the controller knows the mass of the platterstack and the characteristics of the motor and calculates how long it 'should' take for the magnet ( the rotor of the drive motor is a permanent magnet ) to cross the centerpoint. to get an accuratemeasurement we cut out the drive stage at the predicted point for a certain amount of time ( some time before and after ) and we time the exact transition point. The predicted transient point and real transient point delta tells us if we need to slow down the rotating magnetic field or if we can speed it up. The idea is not to break magnetic link between the rotor and the rotating field we create.by 'riding' this point we have maximum acceleration without risk of breaking the magnetic coupling.A harddisk motor is not made to run at different speeds than operational. The bearings simply do not work right and would wear out. so speedup must be fast to avoid damaging the bearings.There is a lot of other things involved. getting it up to speed is one ... keeping it there is another, especially when the heads are moving ...and the velocity needs to be absolutely constant. a harddisk writes 'blind'.. the writing of a block of data is open loop. we detect the servo wedge ( an analog signal recorded on the platter at the beginning of each sector ). the phase and frequency of this serve signal is measured and timing is aligned with the motor controller. The channel processor (the number cruncher that records the bitstreams ) now knows the exactly at what point it can turn on the write current and start sending 1 and 0 into the write coil. but it can only do this for a short time out of fear the phase lock may drift.. if we write too long we would be destroying the servo wedge of the next sector.. or even worse : corrupt a datablock ..the better speed control we have , the less amount of 'dead' zone we need to provide to decrease the risk of overwriting servo. the less dead zones the more bits we can cram per square inch.A harddisk drive is a -very- complex system. You would be amazed what kind of batshit crazy techniques are used to cram more data in there. ( i say 'we'. I design these motor controllers for a living. There's a better than 60% chance that the harddisk in your computer has my controller on it.. The company i work for ships slightly over a million a day to the drive makers )We got Dual stage actuators now.. For people that remember old skool turntables and vinyl discs : the arm sits under a tangent . it is only perfectly aligned with the 'groove' in the middle of the range. move outwards or inwards and there is a 'side' pressure. the same goes in harddisks. what happens is that the recording tip sits under an angle in respect to the magnetic track. this causes magnetic 'leakage' while writing into adjacent tracks as well as crosstalk from nearby tracks when reading. so we put the tip of the head on a piezo actuator and we can now flex the recording head so it does align with the tracks .... we gone from a stiff arm with a pivot point on one end to an arm that pivots on both ends. the heads is always perfectly perpendicular to the track now. very complex servo system...and we are moving into things like laser-assisted recording. a laser heats the area to be written to magnetically 'soften' the data layer. it requires less current in the write coil which means we can build and collapse the field faster and thus write bits closer ... when cooled the material magnetically hardens' so data integrity is good..As for the chip that sits on the headstack itself. That is a little gem too. SiGe (silicon germanium) . Write current 150 .. 300mA. Bandwidth ? 6.7 GHz ...we got flying height control too. to control the right 'depth' of the magnetic field ( the magnetic layer sits not at the surface as y may think but is buried under a diamond-like coating ) we need to control how high we are flying the head above the platter. Bernoulli's law is subject to temperature. so we have a heating element in the heads. but , writing causes heat , so there is two control loops one for writing and another while reading ( more heat required ) if writing goes on for a long time then the heads poles 'grow' ( the heat causes the material to expand and the tip becomes longer. when cooling down it restracts. so stuff like that is compensated for as well.... )Harddisk are a very fascinating technology. to the point it is a wonder it works at all ... the hoops that need jumping through to store a bit and retrieve it are staggering... and for only 40$ .but yeah , you could drive it with cheapaudio amps .. but not for long.

author: IanB
author_rank: Super Contributor
timestamp: May 22, 2012, 02:56:27 pm
content: Presumably all this drive complexity is not needed for floppy or optical drives? Optical drives are often considered as sources of motors to re-use.

author: M. András
author_rank: Super Contributor
timestamp: May 22, 2012, 04:39:49 pm
content: Quote from: free_electron on May 22, 2012, 02:43:55 pmfor curiosity you mention you work in a waferfab, and you design the chips, can i ask which company is this?

author: free_electron
author_rank: Super Contributor
timestamp: May 22, 2012, 06:44:25 pm
content: I started in the waferfab in 1993 , moved to design in 1995 , moved to US in 2000 , moved into harddisk technology in 2005 ( before that i did adsl and bluetooth. )

author: SeanB
author_rank: Super Contributor
timestamp: May 22, 2012, 07:24:23 pm
content: If you want to make a 3 phase supply you just need 3 12V transformers with 115V primary windings. Wire the primary windings in star, and drive the secondary with the 400Hz from a single ended driver. Place 3 2.2 uf capacitors across the output windings ( 1 per phase). the 3 phase input is just a simple 4017 arranged as a divide by 6, with the 3 driver transistors being connected to the even outputs, driven from a 2400Hz oscillator.Not the most elegant design, not terribly efficient and definitely a bad output waveform, but works well enough to drive a gyro motor and will provide enough power to enable the erection motors to run. Those are the motors in the cage, they are switched on by the mercury switches to provide a restoring force to slowly bring the gyro cage back to centre, with a higher power being applied if the fast erect button is pressed. The reason they are slow is that if you fly with a bank for around 5 minutes they will bring the horizon bar back to centre, removing the bank. This is deliberate to allow the gyro to compensate for the rotation of the earth.The original 747 gyro assemblies were sensitive enough that they would detect the motion of the earth around the sun if you ran them up and disabled the restoring force. Run it for 24 hours and you would almost get back to the same angles, the difference being the amount the earth has moved about the sun in the day. Not even Sperry can repair those, they are replaced with new ones if they go faulty. The unit you have is eminently serviceable, even down to the bearing balls being individually replaceable parts.

author: sonicj
author_rank: Frequent Contributor
timestamp: May 22, 2012, 07:39:44 pm
content: Quote from: amyk on May 22, 2012, 08:34:18 amnew, yes! however, i got mine for $15.73usd on eBay.Looks like the core might be worth $2K towards a refurb but you can get a decent new one for around that price or a solid state for a fraction of the price.-sj

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 23, 2012, 01:58:52 am
content: Newer hard drive motors use FDBs which are indeed sensitive to speed, but the (really) old ones used ball bearings and would operate very well over a wide range of speeds. (BTW, MO technology is nothing new - it has been used in numerous removable disk systems like the MiniDisc.)Now I wonder if the write amplifiers out of broken hard drives can be repurposed for WiFi range boosting...

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: May 23, 2012, 12:26:46 pm
content: Quote from: SeanB on May 22, 2012, 07:24:23 pmI'd pretty much concluded these were motors, but wasn't aware they would normally be running. I may investigate driving these as it would be nice to have it moving by itself as a display piece.

author: robrenz
author_rank: Super Contributor
timestamp: May 23, 2012, 12:46:35 pm
content: There are gyrogimbalbearings that have driven intermediate races (like a bearing within a bearing). Those middle races are driven opposite directions on each end of a gimbal. It has 2 purposes, to eliminate the starting torque of the bearing which is higher than the running torque, and whatever bearing drag torque remains is equal and opposite thereby cancelling out. this allows as close to frictionless pivot action possible mechanically.Do you think this has this bearing style and the corresponding motor/s to drive the middle races?

author: SeanB
author_rank: Super Contributor
timestamp: May 23, 2012, 05:18:27 pm
content: No, those motors are only powered when the mercury switch detects the gyro is out of level, and places a very low torque on the axis to restore the gyro to the central level. It is very low and slow, taking minutes to do so so that the motion of the aircraft does not cause it to show an incorrect attitude. It averages out the switch operations so that only the nett effect of a long period is acted on. The motor is a split capacitor motor ( thus the capacitor on the gyro frame in the video) with the switch selecting a direction for reaction, or nothing when the axis is close to level.The fast erection switch simply shorts out a series resistor to change the action from minutes to seconds. If you are not flying level the fast erection will lock in an incorrect attitude that will take a long time to level out.You do have synchro outputs from gyros, but these will not have a motor style core, but will only have a single pole rotor, fed via slip rings, and a 3 phase stator winding. This is normally used to drive either a computer or a 3 axis display ( a ball) remote from the gyro, allowing the gyro to be placed at the mass centre and the display to be at the cockpit a way away, where it will not be affected by false readings during turns or pitching.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: May 23, 2012, 11:11:58 pm
content: QuoteSo would this effectively be single phase, like a normal induction motor with a run capacitor?From memory think there were 4 connectionsQuotePresumably the wirewound pots on this one are used to provide a position signal for external systems - autopilot or co-pilot display perhaps?

author: SeanB
author_rank: Super Contributor
timestamp: May 24, 2012, 05:05:40 am
content: Yes, a simple 115V 400Hz split phase motor. Somewhere there will be either a big resistor, or a choke, to do the 2 torque settings.The pots are probably an output to the autopilot to enable it to do attitude hold, so that it will keep the control inputs it makes to predetermined levels. The pots are probably fed with 26VAC 400Hz, so as to enable noise reduction, by sampling at the phase peak. A very common method on aircraft, where there are a mix of technologies, synchro and resistive sensors will use the same input circuit, and will give the same output as well for the same angle of rotation.