The AM Forum

I am looking for information or suggestions on how to repair/replace the tuning motors in a Collins 300G.

Are replacements available?

Is there a retrofit?

Can the existing motors be repaired or rebuilt?

Thanks
Brian
KB3WFV

I would guess yes if the right motor shop is found and it will take some searching.

The only odd things are the 24VAC power, small size, and whether the shop can do small units as today it is the large units that are considered 'worth it' and the tools or machine shop may be oriented toward that side. They are regular induction motors, right? well so is the motor in my radio shack antenna rotor, so there's nothing weird about it at all.

I'd bet the motors are a third party manufacturer so it may not be a real big deal. There is a shop in Gran Prarie TX that did a 1930s 208V 3HP 3 phase motor for a friend a few years ago. It came back like new. searching https://www.thomasnet.com/  and/or 'manta' for motor rewinding-repair service may be better than trying to use google for this specialty.

What does the motor look like??  Maybe a picture?

Fred

Yes, a picture would be great.I mite be able to rewind them for you.
Regards,
Gary

Unless the windings are fried, the problem is most likely brushes or bearings, or both.  Do the motors turn at all?  If so, it's probably gummed up bearings.  Take the motor apart, lube with appropriate synthetic oil or grease.  Bearings can also be replaced.

Thanks for the replies.

I have been told that the electrical part of the tuning motors work. I am unable to test them at the moment because the momentary tuning control dial (center off - left turns motor one direction - right turns motor the other direction) feels bad to me and most likely should be disassembled and inspected or repaired before applying voltage to to the motors.

Mechanically the tuning motors need attention. The lower tuning motor shaft has a broken tape drive (for lack of a better word) to the tuning slug. The upper tuning motor shaft tape has been discoonected from the tuning slug for some reason. Apparently these tuning motors in the 300g are likely to strip a gear that cannot be replaced. Something else that I wil have to confirm once the switch as been verified or repaired.

I was hoping that someone may have a pair of working motors with intact shafts for sale, but that doesn't seem to be the case. Or a slick way of retrofitting some other tuning method into the Collins 300g.

Nonetheless, here are some pictures, a couple of more will follow in a separate post.

Thanks
Brian
KB3WFV

Close up of the front shafts of the tuning motors.

Not sure about the tuning motors, but those inductors look less than healthy.  It appears the varnish on the wire has been heated to the point where it has failed. 

Joe-W3GMS

Try Paul, WA3VJB, he's had several of those transmitters as i recall and i believe had also parted one out, so if he doesn't have the parts you are looking for, he might be able to point you in the right direction at repairing them.

Paul is already involved.

The tuning motors in the 300G intentionally used a sacrificial phenolic gear in the drive system that would strip and save the motor should the drive system jam. As is more often the case, lack of used caused things to gum up with the same result.

If the motors spin now, chances are the gears are already toast. If they bind, I'd strongly suggest pulling the drives apart and cleaning in the event the gears aren't already chewed up. My motors are all out awaiting replacement gear. Barry Wiseman, the former owner, attached plastic tongue depressors to the coils to allow him to manually tune it. Works but the original system would be nice, of course.

Tom/W2ILA the 300G guru is a member here and can give you other pointers as well, though he travels a lot for his job.

Are replacement gears still available? If not, is it something to where one could make it by casting, using a known good gear to create a mold? Grasping straws mentally.. My dad used to make models by machining or carving the original shape then making silicon molds into which things like epoxy were cast. I hope you can get it repaired.

I would think the gears could be easily produced with a 3D printer.

A sacrificial gear seems like a JS way to protect the motor though.

The coils could use some cleaning and inspecting. Yes Paul WA3VJB is very much involved as this Collins 300G is #147, a transmitter that Paul had helped rescue from WFOY in Florida. Conversation with Paul and some research on the internet indicates that the topic of restoring or replacing the tuning motors on a Collins 300G has not been actively discussed for some time.

I also wonder if a 3D printer can reproduce the unobtainable gear, although I am not familiar with how to create the data file needed to produce the part. Perhaps a good gear can be scanned? I have access to a commercial 3D printer, all I need is the data file to tell the printer what to make.

This shuld be a lot of fun, testing, inspecting, disassembly, repairing amd documenting what I hope will be a solution to restoring these problematic tuning motors.

Brian
KB3WFV

You're right about the gear, Steve - I suspect back in the late 40s phenolic gears were a few cents to produce vs a motor which was probably several dollars or more. They probably had 1000 extra gears made up and put on a shelf, most of which were likely never used. And I'd bet they never expected anyone would still be using these beasts 70 years later - especially a bunch of hams.

Tom and I have discussed the 3d printer idea previously. Finding a good gear to work from is the first step. They all seem to be chewed up, hence the spinning motors with no tuning action. The drawing would be nice, but the 300G manual doesn't have one.

I did speak with a fellow out west who has a 300G in nice shape that was removed from service years ago. Perhaps he can pull a motor and see if he can find one good gear. After that we can crank 'em out by the dozens.

Most 3D printed objects I have handled seemed fragile. Maybe they were made with cheapest plastic.

Yep, get a good gear and scan it.

You might be able to buy the gears from a place like Boston Gear.  They have thousands of different gears.  First you need to know what this gear looks like.

I had some time to test the tuning motors, two will not move at all and one definitely sounds like it has a stripped gear. I was able to verify that 24 volts of ac is present at each motor on the appropriate wires in each direction and that the neutral or ground is good as well. So, the motor selection switch works and the momentary motor control switch also works (despite it feeling mechanically poor).

I pulled out the Grid Tuning motor assembly with the capacitor which was getting power and would turn some and then stop. The gear assembly appears to be bound up, after cleaning the assembly it seems to turn better but still felt too tight. Removing the motor and the primary gear assembly plate lets the capacitor assembly and remaining two gears spin more freely.

At this point I think a more detailed cleaning and lubrication of this assembly will return it to a normal operating tuning motor. Attached are a couple of photos, including one of the Collins manual showing lubrication recommendations. Anyone have any idea what this lubrication would be? Or, any suggestion on what to use to lubricate the gears and shafts with?

Brian
KB3WFV   

Calls for spindle oil.  Clean everything with WD-40 and try good old 3-1 oil.  Unlikely that type motor is bad but probably it needs to be cleaned and oiled too.  If there is a capacitor on the motor try replacing it.  Gears look like standard brass gears but the pinion gear on the motor shaft may be something else.

Fred

In the middle picture, showing the variable capacitor, it appears that the leftmost rotor plate is bent in. The cap should be positioned so that the plates are fully meshed and checked for spacing.

If it is bent, it can be *gently* bent back and away from the stator that's next to it so that it's the same distance apart as all the other surfaces. Outer rotors are most susceptible to bending from contact with other objects.

Thanks Clark. Already straightened it out. The blade was tweaked by me during disassembly. It is amazing how tight 66 year old bolts are.

Brian
KB3WFV

Thanks Fred!

The gear on the motor is an odd duck. It appears to be part of perhaps some sort of clutch assembly? The shaft of the motor is smooth with a pin through it. Then there is a spring, and a hub with tabs on each side. The pin on the shaft drives the tabs on the hub. The hub drives a two step gear. The smaller diameter of the gear slides into the hub, the larger diameter drives the rest of the gear box. The last two items that slide on to the motor shaft before the motor is put in place is a metal washer and then a felt washer.

I am a bit confused as to why the spring an the two piece hub/gear. It seems like the gear will slip in the hub when in a certain position. I'm not sure if this normal operation or if this is a stripped gear or hub or both ?

Any thoughts ?

Brian
KB3WFV

Unlikely that is a stripped gear.  That little motor would not have enough torque to strip a brass gear.  Not sure about the spring, but the motor may have a shaft that moves forward when powered, like a starter in a car.  If so, that section without gear teeth would act as a guide to engage the gears.

Fred

That gear was probably bought as a standard gear and then a portion of the teeth were machined away on a lathe.  That's what it looks like to me.  I use to have 4 lathes, now I'm down to just two.  Five milling machines, now down to just two of them.  Still have five drill presses and one surface grinder.

My father-in-law was a real tool and die maker capable of making gears.  He once told me that by the time you correctly set up the milling machine to make a gear, it was easier to just buy one.

Fred

Two thoughts.

If their is a raised relief on one side, matching an indent on the opposite surface with the spring between them, I'd say that's for a slippage type clutch... Keeps the gears from eating themselves up.

If it's a gear with another gear that slips inside, that can be a 2 speed clutch.  If the motors hit full inertia, possibly then develop enough centrifugal force to overcome the spring pressure and change the gear ratio....  One of my old remote controlled cars had a 2 speed transmission like that.  It would hit a specific speed and shift.  You set the speed by changing the spring inside.

Or I'm out in left field.

--Shane
KD6VXI

Right Fred, the motor shaft moves forward when power is applied to the motor. BTW I picked up a bottle of 3 n 1 oil tonight. Sadly it's a plastic bottle, I'm gonna miss the sound the metal can made when you squeezed it to apply the oil.


Hi Shane, Thanks for the comments. Between You and Fred I think I have it figured out. Attached is a photo of the motor shaft with the pieces on it.

NOTE: THE PIECES ON THE SHAFT ARE IN THE WRONG ORDER IN THIS PHOTO

The correct order should be from RIGHT to LEFT starting at the motor body.

Pin in shaft
A washer ? (blurry picture)
A gear ? (blurry picture)
Spring
Hub
Gear
Washer
Felt washer

In the photo you can see the felt and the washer are in the wrong place (right of the hub and left of the spring). They should be left of the hub and the gear. Sorry I don't have a photo of the correct order (yet).

Understanding:
1) The correct order
2) The motor bolts to a plate (see photo of capacitor assembly with motor).
3) The tip of the motor shaft sticks through a hole in the plate
4) When the motor is installed on the plate the teeth of the left gear mesh with teeth of a gear in the gear box.

It is easy to see that the motor shaft would move to the left (in this photo) or forward as Fred mention, when power is applied. Pushing the shaft through the hole in the plate.

This would push the gear closest to the motor body to the left (in the photo) towards the plate, compressing the spring in to the hub, the left gear, the washer and felt washer which are held in place by the plate.  

This allowss the gear on the right to engage with (I think) the hub. It might engage the gear on the left instead.

When all of the componets are compressed against the motor plate wall the gear on the left turns the gear box which turns the capacitor.

When power is removed the spring pushes the shaft back towards the motor disengaging the hub or outer gear.

This is probably done to prevent gear stripping as Shane had mention or more likely to prevent overshoot or backlash from the desired capacitor setting when power is remove from the ac motor. Overshoot or backlash can occur from motor momentum or a rocking back when the voltage is removed. In other words without this clutch set up one would play a constant game of "opps, too far" and "damn, not far enough".

I have two more motors to go through, as I work on them I will try to get a better picture of the motor shaft an it's parts in the correct order.

I am pretty sure this is the correct line of thinking, any thoughts ?

Brian
KB3WFV

  :)
A working Collins 300G Grid tuning motor.

https://youtu.be/QrG0ijAryvg (https://youtu.be/QrG0ijAryvg)

A working Grid tuning motor with capacitor assembly

https://youtu.be/Iah9gJU1wMY (https://youtu.be/Iah9gJU1wMY)

Now on to the slug tuning motors....

Brian
KB3WFV

Great, you got the whole thing working, pretty cool the way it works.

I was thinking about how much money Collins saved by not having to put knobs on the xmtr. ;D

Yep, I had the same thought. I wonder if Coolins was setting things up for future remote transmitter site control?

Brian
KB3WFV

A working slug tuning motor assembly.

https://youtu.be/YRCmaTxZHRM (https://youtu.be/YRCmaTxZHRM)

I was really lucky with this one. No need to disassembly anything. All that had to be done was some cleaning and some good ole 3 IN ONE oil.

Now on to number 3 and the last motor. Will my luck hold out?

Brian
KB3WFV

That's the Collins way Fred - why make is simple when you can make it complex.

Good to see progress on these motors!  See the March 1954 Service Bulletin enclosed.  The setup of your IPA cap motor is the same as the two motors in the final but many of the IPA motors have survived while most PA motors are gone.
The failure mode on the PA was the internal surface of the ceramic coils were coated with cigarette smoke, dreck and mung.  The tuning motors attempted to push the piston through the ceramic coil but eventually bound and stuck in the mung.  The engineer could hear the motor spinning and plate current was not changing so the motor was kept spinning. The flexible metal push tape got wrapped around the axle and broke (first safety) , then the drive shaft reached its mechanical stop.  At that point the slip clutch (second safety) should have started spinning.  But, the slip clutch no longer slipped because it too was now glued together with cigarette tar, dreck and mung.  So the next and final sacrificial part was the fiber gear.  And that was the death of many a drive motor gear train.

Squeeky clean the gear train and clean/lube the slip clutch (it is the larger aluminum cylinder attached to the large, very fine tooth gear).  The slip clutch should give way relatively easily using hand pressure on the gears.  Clean & polish the inner surfaces of the coils and the aluminum pistons so the pistons slide smoothly without binding.  But be careful removing those coils so as not to let them unwind like I did unless you plan to rewind the coils that scorched.  From what I remember when seeing your transmitter in Florida it was much cleaner than many but still has some accumulation of 60 year old dust/dirt/old grease to flush.

Todd and I have talked about printing new gears so if someone has access to a print solution a few are needed.  There is a bronze gear centered on the fiber gear so that bronze core could be epoxied to the printed gear.  At one point I was in touch with Boston gear but never pushed to finding if they had a replacement.

I have a vague plan to replace the motors with small 24vdc gear motors that will tap into the original gear train.  

73
Tom  

A good Clock builder will be able to fabricate pretty much any gear that you would need.  They do it all the time.  Brass would be the preferred material. 

FWIW

Curt