Closet Cleaning: Pair of Selsyn Motors listed on ebay - Page 1
Forum section: electronics / general

author: Jon Chandler
author_rank: Frequent Contributor
timestamp: January 23, 2011, 02:41:58 am
content: I just listed apairofselsyn motors on ebay.If you're not familiar with these, it's some amazing retro technology. When connected together with a 5 conductor cable, one motor will follow exactly the other motor. Pointers placed on each motor will stay synchronized or the motors can be run at speed and the shafts will stay locked together in phase.This pair of motors happens to be from the US Navy and was probably used as part of the fire control system on the main guns on some ship.Have a look if this interests you...and bid bigThe motors are kind of heavy, so shipping outside the US might be a little costly.Thanks,Jon

author: RayJones
author_rank: Frequent Contributor
timestamp: January 23, 2011, 06:46:07 am
content: Selsyn = synchro's = good stuff.We still use synchro's on our radar systems, have proven more reliable than absolute position encoders a few times now.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: January 23, 2011, 06:54:22 am
content: With a date on them like 1944 , they are fresh too.Sorry I could not hold my self.

author: RayJones
author_rank: Frequent Contributor
timestamp: January 23, 2011, 06:56:28 am
content: And they still probably work to the original specs - no electronics to go belly up!

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: January 23, 2011, 07:04:06 am
content: I was ready to tease you by saying .... I need to check the bearings first..But any way , if some one needs something so specific , there it is ..

author: Jon Chandler
author_rank: Frequent Contributor
timestamp: January 23, 2011, 07:20:31 am
content: I don't even remember where I got them, but they'd lived in peace and quiet for probably 20 years now (I'm dating myself!). They look like they are in great condition - the shafts spin freely by hand. It doesn't look like they were much used where ever they came from.These have always seemed like magic to me. Turn this shaft here and it's exactly replicated some distance away. And it works whether it's a fraction or a turn or spinning many RPM.It's interesting to know that selsyns are still in use today. Truly, there's not much to go wrong with them in an installation.Jon

author: RayJones
author_rank: Frequent Contributor
timestamp: January 23, 2011, 07:34:15 am
content: Hi Jon, I'm possibly stretching the truth a little bit.We tend to use the Tx side of a synchro system - yes they are marked as such.The Tx units have a lower impedance I believe, so if a Rx should stall, it doesn't adversely affect other possible Rx's hooked in parallel.Our Rx's these days tend to be solid state synchro to digital converters, which underneath the covers are really resolver to digital converters (sin/cos).We do however use the Rx versions in "optical aligners" that allow the operator to align the radar with a balloon target shortly after release.The R1/R2 are the rotor within a set of three phase windings, S1/S2/S3.In the selsyn application, both rotors are energised by the same 90V/60Hz source (for the units as advertised).The Tx unit induces appropriate voltages in the S1/S2/S3 windings according to shaft position.If these are connected direct to the Rx unit's matching inputs, the Rx shaft will faithfully follow the Tx shaft.No smoke (preferably), no mirrorsWith our "optical aligners", we still connect the S1/S2/S3 windings, the shaft is locked to the ground, and the voltage developed at the rotor is used to derive a servo feedback to re-align the radar antenna.It is all nifty stuff, and does not really need any fan dangled digital electronics to make it work - though is all done by DSP these days.