Vintage motor questions/discussion

[Dangeruss]

Comm Drops increased electrical conductivity between the brushes and the commutator for more power/rpm. RCCA did an excellent article on Comm Drops back in the day... I'll post a link when I find the article unless someone else beats me to it as it was a neat read.

Found the article but for the life of me I can't get the PDF viewer to open directly to the correct page so... click either the image or the link below and it'll open the July 1994 issue of RCCA from the Library... then you can scroll down to "page 63 of 65" (page 124 & 125 of the actual magazine) to the "Comm Drops: Fact or Fiction" article...



https://www.rc10talk.com/library/?RCCA/1994#7-RCCA_1994_July.pdf

Useless fact- Schottky diodes work exactly like regular diodes, except super fast.

Chotchkie diodes totally had more flair than regular diodes.

[juicedcoupe]

Click on pics for better resolution.

[terry.sc]

What's the theory behind cut brushes?

They were used for a variety of reasons, and any cut reduced the contact area on the comm which reduced friction to give you higher revs and more speed. The downside is it restricted current flow so you had less bottom end power. Because of this I usually used cut brushes in on road cars rather than buggies where you wanted the extra torque. I usually drilled a hole in the centre of my buggy brushes to give a reduced contact area while still covering the full width and length.

I wonder if the cut brushes were primarily intended for "can" motors?

Stock motors have a fixed timing, the rules dictated how much advance a stock motor could have. By using timed brushes you advance the timing on the centre of the brush which will give you more speed but a higher current draw. So your 24 degree fixed timing stock motor would effectively be a 28-30 degree advanced timing motor. Small changes made a lot of difference when you are using 1200-1400mah cells.

Why don't we do some of the things with the motors we did back in the day, such as:
Vary spring rate?
Use a brush to clean the commutator?
Use "com drops"?

Today no one uses open brush motors for racing. The only competition category that uses old style brushed motors is crawling, where they aren't trying to get the most speed and power out of their motors. All the brushed classes I know of today are using cheap sealed can motors which can't be tuned.

What exactly were those electrical bits we soldered on to the motors? They don't seem to be used at all anymore.

Capacitors to reduce electrical noise. Contrary to popular belief modern 2.4Ghz radios are still affected by motor noise, the difference is that old receivers picked up the signal and acted on whatever it received. Modern 2.4Ghz receiver still pick up the same glitchy signals that drowns out the one from your transmitter, but they are now intelligent enough to work out it's not from the transmitter it is bound to and waits until it receives the correct signal. Rather than instantly reacting to it like the old radios, a modern receiver pauses momentarily while switching to a different frequency until it finds the correct clean signal and because to happens at such a high frequency you don't really notice it.

[terry.sc]

I like this thread.

I have a question. When I power up my tx and then the rx, things twitch to neutral as expected. If i let it sit for a bit I can here the a servo doing a small twitch occasionally. Not sure if its the steering or throttle servo. Will need to pull the body so see for sure. Ideas on what this could be? Its a 35 year old RC10, stock MSC, AM Futaba electronics, stock Associated motor.

With a 2.4ghz radio I still have steering servos that make a little noise after sitting powered and centered for a little bit. A quick flip of the steering wheel quiets the servo for a little while. I think it's just how servos are, but I don't buy many brand new servos (I'm a cheapskate).

If it's twitching and actually moving the servo out and back it is picking up a stray signal that is more powerful than what the transmitter is putting out. Can be an electrical spike from a motor starting or a switch closing.

If the servos aren't moving or making tiny movements, that's often due to backlash in the servo. The receiver tells the servo where it should be, and the servo powers its motor to position it. If the servo has moved to centre, the potentiometer tells the servo when it's in the correct position and tells it to stop. Of course the motor cannot stop in exactly the same position every single time, so the servo tries to nudge the motor into the exact place. As servo motors are driven by switching full power on and off very quickly, like the motor ESCs, you hear a high pitched buzzing as it tries to move the motor a tiny amount, but with a tiny amount of power. The motor doesn't move because it has to move the whole gear train and doesn't have enough power to do that, so you hear the buzzing noise until you flick the steering which gives it enough power to start the gears moving.

[Frankentruck]

If it's twitching and actually moving the servo out and back it is picking up a stray signal that is more powerful than what the transmitter is putting out. Can be an electrical spike from a motor starting or a switch closing.

If the servos aren't moving or making tiny movements, that's often due to backlash in the servo. The receiver tells the servo where it should be, and the servo powers its motor to position it. If the servo has moved to centre, the potentiometer tells the servo when it's in the correct position and tells it to stop. Of course the motor cannot stop in exactly the same position every single time, so the servo tries to nudge the motor into the exact place. As servo motors are driven by switching full power on and off very quickly, like the motor ESCs, you hear a high pitched buzzing as it tries to move the motor a tiny amount, but with a tiny amount of power. The motor doesn't move because it has to move the whole gear train and doesn't have enough power to do that, so you hear the buzzing noise until you flick the steering which gives it enough power to start the gears moving.

My servos aren't twitching, they just get dissatisfied with their position and grumble about it a little. Just servos being servos.

[terry.sc]

Yep, play in the mesh between the many gears, or the motor not stopping in exactly the right place, means the potentiometer sees the servo position is very slightly out and tries to correct it without giving enough power to the motor to actually move the gears in the servo.

[Swath]

Most excellent information fellers, many thanks for the great info. I'm relearning things and learning new things I didn't know back in the day.

I still use a lot of brushed motors for my crawlers, I just like em. Ever since my youngest days racing slot cars (pancake motors) where I learned about brushes, brush springs, commutator, rotors and the magnets we could swap out.

Rebuilding this Ultima Pro and going through all my old components raised a number of questions. I appreciate the answers.

[Swath]

My question arose while I am rebuilding this Ultima Pro.

As I await the numerous parts to arrive so I can continue I began to ponder all the motor stuff from back in the day. (88-89 time frame)
These diodes were never attached.
Does anyone know if they are all essentially the same? I know the big round one is the capacitor, but the rest seemed to be used interchangeably.

These next 4 pics are the 4 motors I used back then. I had some set up differently. It seems clear the capacitor should be soldered between the + and -. While the diodes? go from either the + to ground or - to ground.

But in these two stock motors I used just diodes. This was 36-38 years ago, my memory fails me on the why do it this way part.

The brushes I used then, differing cuts, one for timing apparently, others just for the surface area change.

This one which is still installed in a stock motor is cut on two sides.

These brushes I found for sale on the net, I had no idea there were so many different cut types.

Remember these? They used to drain the Ni Cad batteries after use, to a proper storage level.

[Swath]

Some of the stuff still bagged from back in the day. A set of matched batteries for $49! I remember that being quite a bit of money back then. This was the first matched set I bought and never used them.

[RC10th]

Battery bugs were popular for NiCd.

Many used to drill a cavity in the brush and stuff a bit of cotton in it with comm drops.

[1911Colt]

In that first photo with the screwdriver at the top, those are all capacitors. The large one is an electrolytic, which means it is polarized. It has a positive and negative lead and must be installed correctly. The rest are non-polarized and can be installed either way. They are interchangeable as long as they have the same ratings printed on the side. It is possible that the large green one has a different rating. Before folks started using electrolytics, they would often use the larger ones across the tabs in conjunction with 2 smaller ones (1 from each tab to the can). I recall the smaller ones being .01 uf, but don't recall the rating of the larger one (47 uf maybe?).

The "standard" layout is to connect 1 standard cap from the positive tab to the motor can, another standard cap from the negative tab to the motor can, and an electrolytic cap from the positive tab to the negative tab. For sake of appearance, I would use the standard caps in matching pairs.

There were no diodes pictured, but if you want to use one, it goes in parallel with the electrolytic cap. Diodes are polarized as well.

[Swath]

In that first photo with the screwdriver at the top, those are all capacitors....

Great info, thanks. I had no idea they were all capacitors.

[Swath]

Battery bugs were popular for NiCd.

Many used to drill a cavity in the brush and stuff a bit of cotton in it with comm drops.

Comm drops used like that is quite interesting.

[terry.sc]

These diodes were never attached.
Does anyone know if they are all essentially the same? I know the big round one is the capacitor, but the rest seemed to be used interchangeably.

The picture shows various capacitors, the round can one at the top is an electrolytic while the others are ceramic.

All the smaller ones can be used anywhere on the motor, but the electrolytic one is directional. This can be used across the brushes on a motor, only if you have a forwards only speed control. If you use it on reversing speed control, when you select reverse you short out the capacitor, usually the capacitor will blow before it does any damage to the esc though.

[Swath]

All the smaller ones can be used anywhere on the motor, but the electrolytic one is directional. This can be used across the brushes on a motor, only if you have a forwards only speed control. If you use it on reversing speed control, when you select reverse you short out the capacitor, usually the capacitor will blow before it does any damage to the esc though.

That right there is a critical bit of information, thanks!