Cutting a motor commutator & motor tweaks

[Charlie-III]

OK, say you have a motor with a toasted winding and you're "feeling lucky" and want to try your own re-wind, do you measure the unburnt wire over the "varnish" coating, or scrape it down and measure the copper??

I'm assuming it is over the "varnish".

The difference it likely very small, but, it IS a difference, especially when you're looking at "1/2 ga" wires.

For others interested, do a search for "magnet wire" which is usually what you want for re-winds.

[EddieO]

Techincally its the raw copper....as there is no standard on varnish thickness....and you can buy it in different thicknesses. I actually just got some 25t motors wound up with Heavy insulation....just for shits and giggles.

In the end, yer not going to reinvent the wheel here, so just tell me what wind you want to do and which blank you have and I will tell ya what fits....assuming yer talking about a 540 here.

Easy stuff though...

30t on 5mm - 21 easy....20.5 harder, 20 you better be a pro.
35t on 5mm -21 AWG is fairly easy, 21.5 really easy, 20.5 not easy at all.
40t on 5mm - 21.5 not that easy, 22 normal and pretty easy.
45t on 5mm - 22 normal...


Later EddieO

[RcBro]

So when putting a motor on a dyno. What exactly are you guys looking for? And at what Voltage are you testing it at? Mine gives me the max rpm data and max amp date depending upon which test I choose.

[Hulksta]

Originally Posted by RcBro

So when putting a motor on a dyno. What exactly are you guys looking for? And at what Voltage are you testing it at? Mine gives me the max rpm data and max amp date depending upon which test I choose.

For crawler motors your best to aim for max power at 7v

[Charlie-III]

Originally Posted by RcBro

So when putting a motor on a dyno. What exactly are you guys looking for? And at what Voltage are you testing it at? Mine gives me the max rpm data and max amp date depending upon which test I choose.

I do before/after dyno runs. I use 7volts for the most part due to packs I run (use a voltage similar to your normal battery pack).
My dyno has variable loads as well as RPM, so I see what RPM's it pulls vs. load with a "ready to be cleaned up" motor.
Then do maintenance, seat new brushes if they were changed, then repeat the dyno run to see how it looks (are RPM's better at each load).

[RcBro]

Just did this. Man it's addicting and awesome to see the gain and efficiency of a motor after a rebuild and break in.

[Hulksta]

Originally Posted by RcBro

Just did this. Man it's addicting and awesome to see the gain and efficiency of a motor after a rebuild and break in.

That it is when i started out EddieO made a very good point to me about efficiency... dont tune to efficency for a comp rig its not needed (leave that for scale rigs )

What dyno are you using? Ive got a CE & a Robi but havent used the Robi yet, must get around to playing with that one

[73bronco]

I finally bought my own comm lathe and used it for the first time tonight! What a great little tool!! Super easy to use and looks like it did a great job I suppose it is better than sanding the comm with really fine sandpaper(considering I lathed a comm I had sanded and found it to be tapered pretty bad).

Any tips for the "backyard comm lather" to make sure it is done right??

[JohnRobHolmes]

Make sure your bit is super sharp and on center of the comm.

[EddieO]

I guess the basic tips are.......make sure its round, use calipers and make sure the cut is the same at all points. Taper is bad news, good way to hang a brush or chip the comm slots....finish wise, it should look the bottom of CD.......if its super shiny smooth glass looking, more than likely your bit is dull. A good sharp carbide bit works fine, but upgrading to a diamond is worth it.

Like I tell all first time lathe users..........find some old race armatures or something........and practice....if you mess up on one of them, no big deal!

Later EddieO

[Charlie-III]

Originally Posted by EddieO

I guess the basic tips are.......make sure its round, use calipers and make sure the cut is the same at all points. Taper is bad news, good way to hang a brush or chip the comm slots....finish wise, it should look the bottom of CD.......if its super shiny smooth glass looking, more than likely your bit is dull. A good sharp carbide bit works fine, but upgrading to a diamond is worth it.

Like I tell all first time lathe users..........find some old race armatures or something........and practice....if you mess up on one of them, no big deal!

Later EddieO

+1, also cover the comm with black Sharpie marker:
1-It acts like a cutting lube
2-Makes it easier to see where you have cut
3-If you have a lathe with V-blocks supporting the arm (vs. bearings) I use Lock-Eze (graphite lube) where the arm sits on the V-blocks to reduce heat & wear.

[EddieO]

Sharpie trick works....I don't do it, but there is no harm in it.

I am no a fan of graphite on the vblocks.....its messy and the crap gets every where....makes me think I am prepping my axles for the pinewood derby again...I am a fan of just a basic light oil. Bearing oil works just fine.....cleans right off nice and easy.

Later EddieO

Originally Posted by Charlie-III

+1, also cover the comm with black Sharpie marker:
1-It acts like a cutting lube
2-Makes it easier to see where you have cut
3-If you have a lathe with V-blocks supporting the arm (vs. bearings) I use Lock-Eze (graphite lube) where the arm sits on the V-blocks to reduce heat & wear.

[73bronco]

Originally Posted by JohnRobHolmes

Make sure your bit is super sharp and on center of the comm.

It is a diamond bit that looks brand new, very sharp. As far as cutting on the center of the comm...I thought it was supposed to cut just a little off center? This lathe is set up to cut just off center.

I cut a couple old cheapy motors last night and the comms were not super shiny, I thought I screwed up but based on Eddie's response it sounds like they are just about perfect.

The lathe came with V-blocks and rollers, which would you all recommend and why?

[killswitch]

V blocks all the way. Bearings develop slop WAY faster than a properly used v block will. Also, I've seen a copper chip caught between the bearings cause the arm to jump and the bit gouged the comm. Used to see it a lot back in my racing days.

[JohnRobHolmes]

Depending on how the bit is shaped, the cutting edge can indeed vary around center. For copper, we want a tool bit with a lot of clearance and top rake. Alternatively a bit with less top rake and more clearance can be set above center to prevent smearing. A bit with an extreme top rake can still cut well below center. I would assume your lathe is designed for a specific rake angle if the cutting edge is not on center.

V blocks are the best bet for long service.

[Charlie-III]

I say V-blocks for consistencey.......keep them lubed and they will be consistent........

[I'm probably spelling wrong.....sorry]

[73bronco]

Awesome! Thanks to everyone for their input I will definitely run the v-blocks. The bit has a pretty extreme rake to it so I assume, you JRH, are correct that my lathe was designed like this.

[Hulksta]

Haven't needed to do it yet but what's the best way to sharpen a diamond tipped tool?


Sent to you from my dam phone would you believe!
Cheers
Dan

[Charlie-III]

Originally Posted by Hulksta

Haven't needed to do it yet but what's the best way to sharpen a diamond tipped tool?


Sent to you from my dam phone would you believe!
Cheers
Dan

Replace it.......I highly doubt ANYONE here has a way to sharpen a diamond tool.......

[EddieO]

You need to send back a diamond tool to be redone.....not something we can do at home.

Later EddieO