3573 replies to this topic

[Prof. Fate]

Hi

So, the part about drilling out coat hanger didn't give you a clue on the HUMOR intended?

Fate

[Duffy]

Sorry, guys, I tried my best and failed. The drill kept coming out the side of the wire when it got to the hook part.

[Jairus]

Deep conversation...

[havlicek]

Well...I hate to drift this thread, but I finished assembling the #23 wire Mura:




It's not broken in yet...but at 5.5V it positively screams and draws somewhere between 5 and 6 amps. I'm kinda worried about breaking it in, so I'm running it about 30 seconds at a time This thing is a mofo!

-john

[Jairus]

[HarV Wallbanger III]

John it would help with some vintage "Elephant Ears" or Thrinity heatsinks..... REALLY.

(i got'z both.....)

[havlicek]

I'm sure either would help Barney, all I could find when I assembled this one were the little aluminum plates that don't do very much! I have made them in past out of sheet aluminum, a little fiddly but not THAT bad. If you have a pair of either I wouldn't argue with you if you were to let them go eastward Right now, I'm surprised that an arm that would no doubt vaporize an earlier motor seems like it actually has a chance of living in the old Mura. When I get Muras, I will clean up the old setups, replace the bushings, remove the rust, repaint them (in this case the really nice Rusoleum "hammered finish" silver) and set them aside for things like this. On this can, someone had slightly modified the holes so I reamed them out back to round and figured this motor could use the little extra airflow.

-john

[Bill from NH]

That's a beautiful looking motor, John! Although never as popular as the Champion C-can in the northeast, whenever it was used, it was common practice to enlarge the holes to 7/32".

[havlicek]

Hi Bill,

Thanks very mucho! Like I said, whoever had the motor before me had done some rough "customizing" to it so I had to clean it up, but I figure (like you said) the extra breathing room couldn't hurt! This particular motor is one I did just for the enjoyment and experimental value, not for anyone in particular. Whoever does wind up getting it will no doubt have to use it very sparingly (unless I suppose if it winds up as a period drag motor)...I see the motor as being in a nice period chassis and only getting really light use. Still, it's definitely got some impressive muscle and it probably is being "choked" somewhat by the light gauge shunts. On top of all that, a set of the absolute best magnets would probably bring out some more of the "beast" in this thing...along with ball bearings and real heat sinks. There's probably a LOT more potential in this thing that a balls-to-the-walls race setup would take care of. I like the way it looks right now though, sort of like a big block from the factory...before the aftermarket stuff gets installed

-john

[havlicek]

Here, I did up a 26D arm with #29 awg wind...a wind that's one of the ones I favor for a good balance between torque/rpms/ and liveability. With a set of Arcos, and a nice end bell setup, you can really move a period car with this wind and not really have to worry so much. I added a rescued Mura com and it balanced out very nicely:




...it should be a real strong runner

...next up a nice old Mura that really fried. Both brush tubes ("heatsinks") have melted into the endbell and cocked a little so it's going to be a challenge just to get them to sit straight again. Not a "special" motor at all for the day, but now a really nice specimen :




-john

[Victor Poulin]

John,

The 23 Mura came out SWEET !! Hows the heat factor? Im guessing if its pulling that many amps it's prob running pretty hot as well. Your right about breaking it in , in small doses.

I've had a couple that at first ran way hot, but I broke them in just a minute or two at a time and once they settled in and brushes seated they cooled down some. I think you'll find that a motor like this one is prob going to run somewhat hot even after breakin lol.

Still should be a fantastic period drag motor

[havlicek]

Thanks Vic The heat isn't as bad as I was expecting. I've had motors where you could feel them almost instantly get into "dangerous" territory when you power them up, and this isn't at all like that...even with what is a pretty basic Mura setup. There are things that could be added to keep it cooler like I mentioned above...and you could even add a com-cooler. I don't know how much they do...but they sure look bad-***! I was originally going to do 15T/#23 and now that I've run the thing, I'm glad I put the extra 2 turns on there. I also really like the "Hammered Finish" paint for these old Muras. It doesn't look right to me on Mabuchis, but it's a really hard/glossy/durable paint.

-john

[Alchemist]

Hi John,

I was originally going to do 15T/#23 and now that I've run the thing, I'm glad I put the extra 2 turns on there.

May I ask what change in characteristics do you believe would have taken place if you hadn't added the extra 2 turns please?

Thanks John!

Ernie

[havlicek]

Hi Ernie,

what change in characteristics do you believe would have taken place if you hadn't added the extra 2 turns please?

Well for one thing, this would have resulted in an even lower resistance than the stoopid-low resistance as it stands...think more RPMs. It probably would have also passed more current and got even hotter. Because there's always a balance...a "push-pull" going on between the permanent field of the magnets and the alternating fields of the arm coils/poles, it's also possible that going to stronger magnets might have completely changed everything. In theory, more turns should also result in more torque...but there will be diminishing returns there depending on magnet strength, spring strength, available current. There are so many factors at play in a motor that it makes my head hurt to think about them all, so I leave that to the physics experts.

-john

[HarV Wallbanger III]

I dig them out John and send you another care pak. I have a bunch of arms you can rob the comms from ....maybe and some more Mura stuff. I will try to send this week.

[Alchemist]

Well for one thing, this would have resulted in an even lower resistance than the stoopid-low resistance as it stands...think more RPMs. It probably would have also passed more current and got even hotter. Because there's always a balance...a "push-pull" going on between the permanent field of the magnets and the alternating fields of the arm coils/poles, it's also possible that going to stronger magnets might have completely changed everything. In theory, more turns should also result in more torque...but there will be diminishing returns there depending on magnet strength, spring strength, available current. There are so many factors at play in a motor that it makes my head hurt to think about them all, so I leave that to the physics experts.

Thanks for the info John! I appreciate it!

Ernie

[Alchemist]

Pardon me John but I have a few questions regarding your #23 wire Mura you just finished.

Do you feel there would be a significant drop in motor performance if you did not run shunt wires? What is the purpose of shunt wires please? Is it a mandatory practice to employ the use of shunt wire on motors that have certain wire gauge?

I'm trying to understand the use of shunt wire and why some motors have them while others do not.

Thank you for your time.

Ernie

[Jairus]

Electricity follows the path of least resistance.
This is a rule just as is the law of gravity or the the one about a fool and his money.

The current will travel from the brush hood to the brush through contact inside the tube for a while. But as the motor runs dirt begins to build up inside the tube as does carbon from constant sparking. Eventually the resistance builds and power will eventually switch to flowing through the brush spring as resistance builds between the tube and the brush. The brush spring is a poor path for the electrical current due to it's small size and resistance equals heat which is bad. The result can be a weakening spring at the least and a melted spring post at the very worst!

A set of shunt wires provide the electrical current a direct path from the lead wire to the brush. This means no carbon build up in the tube (freely moving brushes) and no power traveling through the brush spring. (consistent spring pressure)
They are not necessary as long as the brush tubes are cleaned with a tube brush from time to time, but the use of shunt wires ensures longevity of operation of the motor with little maintenance required.

It's a good thing!

[havlicek]

Jairus got it right and I pretty much agree with what he says. The current path following the brush hoods to the brush is not that great. The brushes must sit loosely in the hoods or they'd get hung up...so contact there won't provide a good current path...especially if the motor is one that will "ask for a lot of current". The springs themselves are skinny and steel at that...not as good a conductor as brass. I'm not sure when Jairus says that shunts will prevent carbon buildup in the hoods...carbon will build up mostly inside the endbell from wear/contact at the spinning com, and shunts shouldn't really have an effect on that as far as I know. Also, high-amp draw motors can wind up "starved for current" without shunts as the simple contact between the brushes and the hoods may not be solid enough to pass all the current the motor is asking for. So when Jairus says they aren't "necessary" if the brush tubes are cleaned, I would change that a little and say that shunts are "necessary" on any high-current draw motor...maybe anything over a #27 wind. Those motors will run without them for a little while...even if they're not getting enough current, but the springs will often either lose their temper or melt outright from the heat generated by so much current passing through the spring's resistance. Think of the burner element on an electric stove.

-john

[Alchemist]

Thank you Jairus! Thank you John!

I appreciate the both of you taking the time to provide me with the technical information I was hoping to acquire.

Really appreciate it!

Ernie

[havlicek]

...couple of more things about shunts Ernie:

1)Shunts are like guns, better to have them and not need them to not have them and need them. In other words, shunts by themselves (and if installed and functioning properly) will never hurt a motor's performance. When installed on a motor that doesn't "need them", the motor will run just as well as it did without them. So (and this falls in line with Jairus' recommendations), if you have a motor that you think may need them, by all means stick 'em on there.

2)If improperly installed and causing the brushes to get hung up, shunts may not only hurt a motor's performance...they could burn it up. Doing a nice job with shunts is pretty fiddly and often may mean modifying the brush hardware and you may have to reinstall them when you change brushes, so it does add a maintenance thing. I've seen some super-tidy shunt installations here by Rick T and others, so look around for ideas about how to get the job done. I got some teensy-weensy eyelets with crimp connectors on the other end from Kim Lander that would make it possible to connect the shunts under one of the endbell hardware screws...pretty neat! So there are many different variations on how to install shunts. People have even posted pictures here in the past on how they do it and might post some again.

3)If you run the motor no load at low voltage...say around 5V, and you feel the springs getting hot after 15-20 seconds, the motor will probably do better with shunts and spring insulation. That heat is from too much current passing through those skinny steel wire springs.

4)Spring insulation is there to break the current path through the springs. You can put it on the short leg of the spring or the long leg...or even both, any should work but if on the short leg, you have to make sure the spring will still fit easily through the slot in the hoods. You don't want the spring or the brush getting hung up because of the shunt or the insulation. Since electricity will follow the path of least resistance, you would think that spring insulation might not be necessary on a moderately high amp draw motor. Since the shunt wire is a much better conductor than the spring, it would seem like current would mostly flow only through the shunt. It seems though as if current will flow through both if the spring isn't insulated, maybe more so if the motor needs a lot of current. Probably a good idea to always insulate the springs if you're adding shunts.

-john

[Alchemist]

Hi John,

Thank you for the additional info. I will definitely need to read this a few or more times to fully appreciate and understand what you are stating about shunts.

Thanks again for your time.

Ernie

[Gus Kelley]

Hey Guys! I tried to do a search in this section for the answer to my question but the format of this blog didn't allow me or I don't know how to do the search. What is a "Hemi" wind VS a regular wind? Gus in Sacto

[tonyp]

A hemi wind vs a std wind is the way the wire comes off the comm onto the stack. A standard wind the wire goes from the tab over the top of the laminations and around the pole. A hemi the wire comes off the comm and goes straight down then around the pole. A hemi has a little less wire for the same number of turns and runs in reverse rotation.

On a hemi the wires do not cross over each other at the comm tab.

[Gus Kelley]

Hey TonyP! Thanks! I guess there would be oh! solittle less resistance but is there some some possible more chance of throwing the wind? Gus in Sacto