170 replies to this topic

[idare2bdul]

I've been revving these things to full RPMs with no load for a while now and they seem to be holding up fine.

No load at full power isn't a good idea, especially with a home-wound arm. Throwing the wire off your arm or blowing up the comm can be a problem. In the early '80s the military tested an arm at over 250,000 rpm at 9 volts no load before it blew. They were looking to power a gyroscope for smart bombs.

One of my friends blew up a motor and imbedded parts in his hand by blowing compressed air into the motor to spin it up with no brushes in the motor.

[havlicek]

"Screaming" isn't the issue. For "scream", you could try 12/22!

But on the track, depending on the track and car, you will likely find that your "screamer" isn't the hot motor.

... well, that's understood as I have done this before and realize that torque is just as important as revs (although to a certain extent a balance in favor of one over the other can be mitigated with the right gear ratio). I have also experimented with winds above and below, thanks to the supply of arms from Ron (thanks again!). I have also installed these arms in cars and revved them to try and get a "feel" for how fast they spin-up... not just how high they rev. Still, thanks for the input!

No load at full power isn't a good idea, especially with a home-wound arm. Throwing the wire off your arm or blowing up the comm can be a problem. In the early '80s the military tested an arm at over 250,000 rpm at 9 volts no load before it blew.

I can always wind more.

One of my friends blew up a motor and imbedded parts in his hand by blowing compressed air into the motor to spin it up with no brushes in the motor.

While I can't really see the point in that exercise, as a carpenter I've lost bits of my hands and other parts over the years. After the wounds have scarred-over and the memory is still fresh I have learned to be prudent about safety. Still... I certainly don't advocate doing anything dangerous. However, we aren't talking about experimenting with rocket engines or explosives here. This stuff is pretty "safe" in the scheme of things.

[havlicek]

I got the Mura blank arms and commutators in and did one up:



These are really nice arms. The stack profile allows for a lot of room to wind and the comm has loads of room on the tabs to solder in that nasty #24 wire. :-) If anyone here (besides Pablo ) is at all interested in doing some motor winding, these are by far the nicest blanks I've messed with so far.

[MarcusPHagen]

Thanks for posting your results, John. Those _do_ look nice! Once I get caught up on housecleaning for the holidays (the "honey-do" list) and get to my watchmaking backlog, I'll have enough cash to buy one of Rick's rewinders and a few blanks with comms to do some winding. It'll be great to be back.

[havlicek]

Hey Marcus,

I hear you about the cash thing... especially with the housing market in the toilet (I'm a carpenter/builder). I've had really good results rewinding those D-can arms as well and have some ready to go into a car when I get that sorted. I also got (thanks to Pablo!) a Champion blank that was excellent, but these Mura C-can blanks are the best so far. They would be really easy to do a double-wind on as well, thanks to the room at both the comm as well as on the stack itself. When I get the balancer from Rick, I'm going to go over all the arms I've kept so far and see if they can be improved a bit. The last piece in the puzzle is Kevlar and I found some on Amazon for pretty cheap (like $2 for a 50 yard spool). These last arms I've been tying-up with fiberglass... but I have to believe that Kevlar will be even more "bulletproof".

So my little trip back into winding/rewinding arms has confirmed that:

1) With a little practice, you CAN whip-up some armatures that will be as good as the factory stuff! You can wind them hot as heck... or not so hot, but in the end it's cool to have a motor you wound sitting in a car you built. Now if I could only paint as well a Jairus or Noose... or build a chassis as good as Rick and some others around here... (sigh).

2) The D-can arms from Ron were super as a way to get back into all this. Being as cheap as they are... and easy to unwind/salvage... you can afford to try things out and not worry too much. When they're done, those arms can be "keepers", too. Their basic components may not be "top shelf"... but they work fine. I've got one D-can setup that rips... and have three backup arms. :-)

3) There's really no "black magic" involved here. This stuff can easily be learned and polished-up with a little practice. Pablo is someone who proves that and like he says... "it ain't braggin' if you can back it up!".

4) Once you get comfortable with all this, the Mura C-can blanks are the bee's knees. The problem with them is that for an arm and a com, you're paying $14 and you don't want to mess up at that point.

5) While static balancing is not the best... it's entirely appropriate for this stuff and all it takes is some patience and care to get these arms singing soprano. It's just a personal preference of mine to "do it all"... but I can see how others would want to send their arms out to be trued, epoxied, and balanced.

I've learned or relearned... I can't remember exactly what is stuff I knew and forgot or just stuff I never figured out before... a bunch from all this, which was cool in itself. You know what they say about once you stop learning...

[GTPJoe]

John,

So when can we start putting our orders in for "custom" arms??

Seriously! I wanna go to the local raceway and have the other racers asking..."So what are you running?" and replying ..."It's a Havlicek 24!!".

How cool would that be!!

I'll buy some single 24s for my Mura setups. 17t of 24 please!

Awesome job!

[havlicek]

Hi Joe,

I'm not looking to go into the arm-winding business, but I am going to give away a couple just to have folks give me their impressions. If you want, you can get one of those. With the Mura blanks costing about $14 each and around an hour and a half in labor for each arm, I would have to seriously set up for mass production to make it all economically feasible-attractive. After I get the "Rick-Balancer" and the Kevlar, I'll do a couple to send out. This way... nobody can complain about the cost :-)

BTW... 17 turns of #24 should be a nice medium-spicy meatball. :-)

Take care, Joe.

[Pablo]

Remember, on the R-Geo balancer, taper the ends of the shaft for best results. The more precise and fine the taper, the easier it will be to find the heavy spot.

Also, with the amount of care that goes into a Havlicek, you may well find it difficult to decide on a heavy spot. In such a case, you must force yourself to believe you did such a careful job, the arm is already very close to being balanced perfectly. Taper some junk arms first, and get the feel of that balancer. It works.

Dynamic balancing is overrated and you can true a comm by using a poor man's lathe (drill) and 2,000 grit sandpaper. WhoooHoooo, somebody just shoot me.

[slotbaker]

Great thread, John.

A few months ago, I did my first rewind on a 36D in 40 years, and it was gratifying to have it work. It even ran pretty quick, as well.

Remember, on the RGeo balancer, taper the ends of the shaft for best results. The more precise and fine the taper, the easier it will be to find the heavy spot.

I asked this question in another thread, but it must have been overlooked.

With Rick's balancer, how accurate does the tapered point have to be relative to the centre line of the shaft? I'm thinking that the magnetic 'pull' would be greatest at the very end of the point, and therefor be the pivot point of the arm. Then, if the point was not perfectly on the centre line, could the balance be affected??

If so, then by being a few thou off centre, could it result in significant weight out of balance?

I love the simplicity of the balancer, and maybe I'm overthinking a non-existent problem.

[havlicek]

Thanks for the reminder, Pablo... I had been told that by Rick as well and it makes sense. The smaller the contact point, the less friction and whatnot. I have a bunch of arms here... both keepers that I want a second shot at balancing... and junkers that I can experiment with.

I wonder what your experience has been with static balancing. So far, I am certain about a small error point past which I can only get by luck. What I mean by that is I can balance two arms and have visually the same result using razor blades... but one will run smoother than the other. Of course, the faster the arm spins... the more noticeable any small errors will be. As well as my best D-can arm runs... my first try with the Mura C-can blank seems much stronger still (!?), but I notice some small vibration. I'm hoping to get a little more in balancing precision from the R-Geo balancer. Between that and tieing the arms with Kevlar... I'm feeling more confident about these things every time I do one.

Here's another question for you Pablo... or anyone else looking in that knows. While surfing the net for info about Kevlar, I came across a forum somewhere and someone said that using super glue on the Kevlar was a super-strong and heat-resistant way to use the stuff. Does anyone know what the safe working temps for cyanoacrylate are versus generally good (but not NASA-spec) epoxy?

[Pablo]

Steve, I'll just repeat myself, "The more precise and fine the taper, the easier it will be to find the heavy spot."

A perfect 45 degree taper would be ideal. Me? I just chucked up my arm in a drill, donned eye protection, and hit the ends of the shafts with a spinning Dremel. No machine shop here.

[slotbaker]

I guess it's just a case of suck it and see.

[havlicek]

Steve,

Like you, I get a charge from doing this and comparing the arms I've wound to some Grp20s I have here... they seem stronger. Pablo's method of having the arm spinning in a drill and hitting the ends with a Dremel will produce a pretty darned well-centered point on the shaft end... certainly good enough for all this. The razor blade thing has other more significant limitations as well. A tiny amount of runout of the shaft itself could make the arm appear to be out of balance. Seemingly invisible particles on either the shaft or the blades seem like boulders and will stop the arm from rotating. Then there's the whole deal about handling razor blades themselves... and those edges go dull pretty fast.

Like Pablo... I don't have any machining tools here, I wish I did! You can get by just fine though with the basic stuff.

[Pablo]

A tiny amount of runout of the shaft itself could make the arm

I'll remind you again, don't spend your precious time and effort on arms with bent shafts. Not really a concern when buying quality new products from known sources, BUT vintage arms found on eBay are suspect, as they have probably been inspected, rejected, and repackaged.

BTW, John, how straight is the Champion blank? I never checked it. As far as I know, it is original, and unopened. I would never send a reject to a friend.

[havlicek]

... Well, in keeping with my low-tech methods... I don't own a dial indicator , but it seems straight and presented no problems balancing it. It's a strong runner right now (THANKS!). Still, when you're dealing with things on this scale visually unnoticeable runout could mess things up. Like you, I wouldn't have much faith in a vintage arm from eBay. As long as there are quality blanks (like the Muras!)... why bother?

BTW... I did some quick checking and cyanoacrylate glues aren't very well-suited to high-temps apparently.

[Bill from NH]

I just chucked up my arm in a drill, donned eye protection, and hit the ends of the shafts with a spinning Dremel. No machine shop here.

This procedure works great for creating a height gauge (scribe) when making inline brackets for FK type motors, too.

[Prof. Fate]

Hi,

Do NOT use cyanoacrylate glues for this. When CA burns, the fumes are toxic.

Fate

[havlicek]

...and a 26 double wind (something different). This one's not going to get tied-off, epoxied, and balanced until after I get the Kevlar... but that's the easy part

[havlicek]

... And here it is fresh from the oven. All tied-up with Kevlar and epoxied.



Now, with my R-Geo balancer on the way (thanks, Rick!) I feel confident that I've taken this stuff as far as I need to to get solid performance from home-brewed arms. The RGeo winder has been a GREAT help here as well... not just for the actual arm winding, but it also makes a dandy "vise" for working on the arms after winding for silver-soldering the comm tabs and tying-off the arm with the Kevlar. If I can do it... anyone can.

[Pablo]

Awesome. Looks like a missile.

[Jairus]

That is beautiful work there, John! Have you tested any of them on the track yet?

[havlicek]

Thanks, Pablo and Jairus... hey, Jairus, I'm looking for a test pilot, and the learning arm I sent you is probably better used as a sinker than to go into any of your creations. Check your PMs... hokey-dokey?

[slotbaker]

All looks great, John.

Just need a trademark arm dye, eh.

[Jairus]

Sinker? What are you talking about, Willis?

[havlicek]

... That's s'posed to be "watchoo talkin' 'bowt, Willis?"

I cleaned-up the comm on the 24 single fer you, Jairus, and wrapped it up. It's going out tomorrow morning... Thanks!