Variable Speed Control or Contraption of Merit?

[Charles Lessig]

Here is a video my friend made at our meeting of the Chesapeake Area
Metalworking Society in Maryland USA. Our discussion did not come
through so you don't need to turn on the sound.

http://www.youtube.com/watch?v=eKzTW...ature=youtu.be

It is a differential variable speed control mechanism mostly copied
from others' designs. I built it to help me understand how they work.

There is a variable belt drive of limited range and a fixed ratio chain
drive connected to a differential which compares them and provides
the output.

Differential speed controls have an extremely wide range of ratios since they can cross zero.

The video shows what is going on pretty well. The wheel drive part
got finished only a couple hours before I left for the meeting. It
shows better than looking at the drive sprocket that is sort of buried.

The neutral here is a bit odd since it is not disengaged but an infinitely
low gear.

The only thing I think is new is the skate wheel differential. I had no suitable gears for the differential and thought it would be quieter at
high speeds.

Pressure on the skate wheels is not constant. The idea was to use
them as a true disengaged neutral but that happened at at one of
the high speed ends of the range and not near low so a better way
is needed to make them disengage for that to be useful.

Gears would carry torque better. The limit would be the belt.

[rohart]

Charles - That looks as if it is fascinating, but I can't tell what is happening.

I know my display shows dark stuff as too dark, and I can grab and enhance single frames because of that. What would be better is a good still photograph with annotations - this is called the XXX and does YYY.

Or alternatively, a more close up video with sound as the designer goes through the workings.

Like I said, it looks fascinating.

[Edwin Dirnbeck]

Charles ,this is a very nice piece of work.I too have pondered various diferential speed control mechanisms .One can easily see that you are changing the speed and direction. My question is does this mechanism also provide an increase in torque as the output speed goes down. Keep up the fine work.Good health to you .Ed

[Charles Lessig]

Charles ,this is a very nice piece of work.I too have pondered various diferential speed control mechanisms .One can easily see that you are changing the speed and direction. My question is does this mechanism also provide an increase in torque as the output speed goes down. Keep up the fine work.Good health to you .Ed

Thank you Ed. I believe the torque goes up as the speed is geared down.
The drive I built is limited by the friction of the belt and skate wheels.

Here is a commercial unit that looks like it won't slip and should have
some mechanism to protect it as the reduction nears infinity.

http://www.specontransmission.com/products/10/MD.php

It is fairly complicated and I'm not sure exactly what is going on.

The unit I made might be good for a scooter or lawn mower.

Best regards, Charles

[RB211]

I think I have seen these before...

[darryl]

One of the configurations I've seen uses a motor on each side of differential gearing. If both motors are spinning at the same rpm, the output from the center gears is zero rpm. Using it in pure electric fashion, the output torque available can be double that of the weakest motor, but it does depend on the relative rpms of the two motors. In this mode, you cannot increase the output torque beyond two times the motor torque capability.

If you add a flywheel to one motor, and a brake to the other one, you can get a much higher short-term torque output. If you use the motor with the flywheel as a generator, you can feed that juice to the opposite motor. While that motor revs up, the other one is slowing down, and the output shaft speed builds up.

You can use the generator/motor balancing act to drive a vehicle. Normally, you would arrange for the electronic balancing act to spin up the flywheel to absorb braking energy, then use that energy to augment battery power to re-accelerate or begin moving from stopped. Having a brake on the side opposite the flywheel gives you the option to send a higher torque to the output than either motor can supply. Using the brake wastes energy, but it's only used for short periods of time- the rest of the time the motor on the flywheel is used as a generator until the flywheel rpm is too low, and the other motor is the main drive motor.

This type of system can use either a planetary gear set or a differential gear set such as found in a rear axle.

[Optics Curmudgeon]

http://bbs.homeshopmachinist.net/showthread.php?t=41469