Cutting a motor commutator & motor tweaks

[SlickRockSpider]

Originally Posted by Cordwood

Holy sh*t that's some serious amps for a little 540. That 55t must of been screaming for mercy. What 7 volt battery did you use that let it draw 500 amps?

"Nothing got damaged but there was a bit of smoke."

My luck and we would have been a Fire. Even if I had 100C rating on my 2 cell lipo.
I have a carbon pile automotive battery tester. Its good for 500 amps at 12 volts.
Now that sounds like a fun day in the back yard.

Evan

[Cordwood]

Originally Posted by SlickRockSpider

Because it was on a bench maybe he used a dc power supply ??? I guess not.


Evan

A 500 amp 7 volt power supply?......

[JohnRobHolmes]

Just good batteries and less than a foot of 12ga wire.

Now the real question is where the motor saturates and stops producing more torque, and starts being a space heater.

[Charlie-III]

Originally Posted by JohnRobHolmes

A fuse wouldn't catch it quick enough before the FET goes, unless the FET is way over rated. In that case the next weakest link goes, which is normally a PCB trace. The only real solution is pulse by pulse current monitoring with a high enough impedance in the system to help clamp the current before things melt down. None of the old brushed motor tools had current limiting, they are all simple pulse width modulators with no feedback circuits.

Yep, fuses are not fast enough....even specific fuses (like "transistor" fuses).....diodes can help, but even they can be overpowered........

A clamping bar may be enough....it's a bit above my electrical knowledge....

[Charlie-III]

Originally Posted by JohnRobHolmes

Just good batteries and less than a foot of 12ga wire.

Now the real question is where the motor saturates and stops producing more torque, and starts being a space heater.

Yep, power supplies have a hard time keeping up with a decent battery source.....since I work with large (30KVA-1400KVA) UPS systems....there is little to compare to a "shorted" battery!!

[Onebdgti]

What is the benefit of cutting the leading edge of a brush. I have heard of people doing it but have never seen it till I took a motor apart and saw it.

[Charlie-III]

Originally Posted by Onebdgti

What is the benefit of cutting the leading edge of a brush. I have heard of people doing it but have never seen it till I took a motor apart and saw it.

For "fixed timing" motors, it allowed changing the timing of the motor since you can't rotate the endbell.

[Onebdgti]

But this was done on a motor that you can change the timing.

[JohnRobHolmes]

It would reduce the commutation duration, making the motor a bit more efficient and have less power. If you had to choose between two motor winds and one was too fast and one was too slow, brush thinning is a good way to get the faster motor dialed down a bit.

[schiesz]

The best thread on RCC needed something to get it bumped back up, so I got my new (to me) Twister lathe going last night. I read this whole thread a few months back, and just started reading it again a few days ago

You guys looked like you were having way too much fun in here, so I had to give it a shot.







First arm cut was from an old twister a friend gave me in college. The next was out of an old Integy 55T I had here. Then I started working on a big comm Reedy that the seller threw in with the lathe.

The twister lathe came in a plastic tackle box type carry case and came with some extra bits and shims and some thing that I don't know what it is. Its a nice little kit though. I am running it on 3.3V from a PC power supply right now, but based on the finish I am getting I wonder if I should try it at 5V instead. The first 2 comms cut looked great, then they started getting dull looking with lines on them. I am feeding it slow, probably at least 30 seconds per cut. I switched the bit that was on it for a new one (figuring maybe the bit was dull), and that didn't seem to change the finish. It is also possible that I have the bit on wrong, or something stupid like that, but I think I am good.

Also, a couple of the bits it came with appear to be left cut, and I think I need right cut bits with this one. Can anyone confirm/deny?

[stanmondz]

i dont remember which direction my was running, but i got much cleaner cyts when i swapped the drive motor leads to run the other direction. i can look when i get home and let you know which way im spinning now.

im running 5V from the PC power supply that feeds my chargers. i just added a 5V tap off one of the red wires, and the same ground as the 12v side

[Charlie-III]

Originally Posted by stanmondz

I don't remember which direction mine was running, but I got much cleaner cuts when I swapped the drive motor leads to run the other direction. I can look when I get home and let you know which way I'm spinning now.

I'm running 5V from the PC power supply that feeds my chargers. I just added a 5V tap off one of the red wires, and the same ground as the 12V side

You have to be careful on drive motor rotation.
The lathe pictured wants the copper to be cut to come up from the bottom to the tool, NOT over the top to the tool.
This helps "pull" the comm into the shaft rests rather than trying to pop it out.
As to power, I use a charged 4 cell NiMH (~5 volts).

[TEDROCKZ]

I have a Twister lathe. It uses the AR(right) its and runs with normal polarity. You want the top of the arm turn away from you or the arm turning up toward the bit(same thing). 5 volt will most likely cut a bit smoother than the 3.3. You may have to shim the bit up or down. Most instructions I've seen say .001-.005 above the center of the arm.

It is a good lathe you did not do bad in finding one

[stanmondz]

mine is turning clockwise (comm spinning up into the bit) it was wired counter clock wise when i got it and the arm was jumping around bad

[TEDROCKZ]

Depending on the make and style of the lathe the motor wires different. Most AR type wire regular polarity and most AL type wire reversed polarity.

Most common AR
Twister
Orion T4000
Trinity
Fantoms

Most common AL
Hudy
Team Orion Mod lathe
Cobras


The last lathe I bought(used AL style) come with a 27 turn fixed timed stocker that was wired reversed and it would get pretty warm.

[stanmondz]

CW/CCW determined by looking at the shaft spinning, or with the shaft facing away from you?

mines the old nasty cobra off ebay a few pages back

[TEDROCKZ]

I really don't use the CW/CCW wording. Just set the lathe like you are using it and the arm should be turning away from you looking at the top of the arm. The Cobra wires reversed -/+

[ultimate_monkey]

been alot of reading in this thread, and im looking at getting a lathe, but there is sooo many choices..

can any one recomend me a complete ready to go out of the box lathe? every thing i seem to find you need to buy all the cutters etc seperatly :S

links where i can order directly are always nice too! haha

[schiesz]

Originally Posted by ultimate_monkey

been alot of reading in this thread, and im looking at getting a lathe, but there is sooo many choices..

can any one recomend me a complete ready to go out of the box lathe? every thing i seem to find you need to buy all the cutters etc seperatly :S

links where i can order directly are always nice too! haha

Well, i've been reading the thread for a long time, and watching for deals on the RC sites and ebay. I just ran across the Twister a little bit ago on ebay, made an offer and the guy took it. It came with everything I needed to start, and it was in a padded tackle box type case. I'd suggest the same for you, especially if you want to spend about $50 like I did

For the tooling, as it has been stated many times in this thread, different lathes require different types... Mine uses AR tooling, but you can get either kind in carbide at McMaster for under $4. All these comm lathes use the 1/4" shank.

[TEDROCKZ]

I guess your budget would be a factor.

You want the best of the best
Holmes Hobbies / Holmes Bikes :: Motors :: Brushed Replacement Parts and Service Tools :: Fantom Factory Commutator Lathe

EddieO @Br00d had some really good one at one time to. The H.A.R.D. brand. No link

Probably the best bang for the buck for new
Motor Lathes & Parts for Slot Cars, RC Cars & Trucks R/C or RC - Team Integy

Best of new and used and my favorite place. Good deals come through pretty regular
lathe | eBay

Originally Posted by ultimate_monkey

been alot of reading in this thread, and im looking at getting a lathe, but there is sooo many choices..

can any one recomend me a complete ready to go out of the box lathe? every thing i seem to find you need to buy all the cutters etc seperatly :S

links where i can order directly are always nice too! haha