Interesting speed reducer mechanism
 

I thought this speed reducer was interesting: http://www.zero-max.com/products/drives/drivesmain.asp

Check the animated GIF at the bottom.

Re: Interesting speed reducer mechanism
 

So... this reduces the speed, but I guess it doesn't do anything with the torque. Plus... wouldnt this cause very jerky rotation on the output shaft?

Sorry if i'm all wrong here... i'm not much of a mechanical engineer when it comes to levers... :o

Its a really cool way to reduct eh RMS speed of the output shaft though...

-q

Re: Interesting speed reducer mechanism
 

The high speed ratchet reduction system... I've never seen anything like it... very, very cool. And since I've never seen or worked with anything quite like it, the following comments are based upon my impression of the animation and description of the mechanism... those with more experience or insight are invited to add to or correct them.

I suspect since the input would be just under 2000 RPM that the jerks would be fairly small. At an output speed of 20 RPM for instance, there would be 100 "jerks" per revolution... not so different from stepper motors, perhaps... as the output sped up, well, at 400 RPM there would be five "jerks" per rev. A bit more coarse, but considering the speed, perhaps not a problem.

It would also have to magnify torque in inverse proportion to the reduction in speed... or else give off a LOT of heat. This is because power = torque x rpm. If you reduce the input speed without increasing the output torque, then you have a whole bunch of power that has nowhere to go... which leaves me wondering a bit about their claim of "constant torque across the speed range".... this must require changes in the speed and/or torque on the input shaft.

Jason

P.S. The real questions are... how efficient is it, and does a CIM mount to it easily....

Re: Interesting speed reducer mechanism
 

I like the idea but I see a few problems with it

1. The output can only rotate in one direction since it employs one was clutches. As a result one would have to use a trans to reverse the direction for a drive train or the like.

2. In any situation this looks really heavy and really complex. I certainly think it has its aplications but robotics seems iffy.

I would actually really like to get my hands on one of these. I would be really tempted to make one myself if I had the time.

Re: Interesting speed reducer mechanism
 

Isnt that true only if the input and output shafts are constantly connected? What I think happens in this transmission is that the output shaft is, in a manner of speaking, periodically engaged and disengaged in small increments from the input shaft, and depending on where you put the lever, it changes how much of the time the shaft is disengaged. Something like a Pulse Width Modulator in hardware.

As with electrical PWM, though there is less power output (due to lower duty cycle) there is no loss, since instead of doing resistive (linear) control of the output, we're just engaging/disengaging from the power source in varying ratios... weather the power source be an input torque or an input voltage source.

Anybody else?

-q

Re: Interesting speed reducer mechanism
 

I think I'd need to CAD this out a bit to figure out the relationships between the controller arm and 2 shafts before I truely understand how this thing works. Infinite amounts of steps in between two speeds seems a bit far fetched from that particular description/animation -- if the controller arm lengthens, should at least the arm to the output shaft have to lengthen as well?

I also question its reliability under heavy stress as well, as unintentional forces from defenders and bumping could stress the ratcheting output shaft in directions that were not designed for -- if the shock of being bumped is normal to the rachet (i.e. parallel to the output shaft) I believe the ratchet could miss/grind a couple of teeth or come off its track altogether. I wonder what amount of torque would break mechanism if it were stalled.

Neat concept.

Re: Interesting speed reducer mechanism
 

We may be describing the same thing, but in different ways. The analogy to PWM control is an excellent one. If a speed control is set up so that a motor draws 100 watts, then the load on the power source is 100 watts plus whatever the speed controller gives off in heat. If the duty cycle is increased so that the motor draws 200 watts, then the load on the power supply is just over 200 watts.

Electric watts (voltage x current) are the same as mechanical watts (rpm x torque), and power in must equal power out (plus heat loss due to inefficiencies).

So when driving our robot motors (we'll assume a constant voltage situation), when you use PWM to chop the average current to the motor you get a lower motor speed... but you also get a lower current draw on the battery. In this mechanism since you are lowering the speed of the output shaft, relative to the input shaft, it must also increase the torque on the output shaft relative to the input shaft in order to keep the power equations balanced.

Like I say... I think we're both kind of getting at the same thing from different ways, rather than debating a point here, and the PWM model is an excellent way of looking at this system for people familiar with speed controls.

Jason

Re: Interesting speed reducer mechanism
 

I don't know, I think it is easier to simply say that If the tourque didn't increase as the speed decreased the box would start getting hot a lot faster than normal or would start vibrating a lot. Which ever way the power comes out if your talking 100 watts of lost power I would think that it would become pretty obvious.

From what I see I think the way that it effects to output speed is by changing the length of the arc that the output shaft moves through every time the lever engages the clutch. For higher output speeds it move the lever through a very large arc and for lower output speeds it moves the lever through a small arc.

Thats what I get from looking at the animation.

Re: Interesting speed reducer mechanism
 

When i was explaining this in PWM terms... i was referring to the fact that while the RMS power throughput of this transmission does decrease with the speed... however while a 'jerk' is taking place, the output shaft is connected to the input shaft, in a 1:1 configuration. The only power that is lost is due to friction, since the two shafts are either directly connected, or completely disconnected. This would cause the input shaft's load to drop near zero (constant voltage) while the two shafts are not 'jerking', and when 'jerking, the motor would take the full torque of the output.

It moves like a stepper motor... just varys the number of degrees of revolution of the input shaft are connected to the output shaft... kind of like periodically engaging/disengaging a clutch VERY RAPIDLY, making little tiny high frequency steps of the output shaft. It does not change the torque, it does not generate heat (besides friction).

</engineering soapbox>

-q

Re: Interesting speed reducer mechanism
 

But the output shaft is directly connected to the input shaft constantly because the animation is only 1/4 of the actuall mechanism. The acutall mechanism inslude 4 sets of of levers so the output is constantly being provided with power.

The reason that the output tourque would increase is not because the length of the lever on the one way clutch is increasing but because you are pushing at it from a different angle. An angle that simulates a longer lever.

Also you can think of it in terms of the movement of the shafts. If there were just one cam then the output shaft would only move when the levers were moving in one direction and be stationary the rest of the time. The levers would be moving in the right direction while the input shaft was moving through 180 degrees of arc. No matter how big an arc the output moves through, the arc that the input shaft is pushing for is 180 degrees. During that time if the output moves through 90 degrees then the reduction is 1:2 and there is twice as much output torque as input torque (during the push). If you then change the arc so that for 180 degrees of imput you get 45 degrees of output I really don't care what happens when the output is stop there has to be a reduction of 1:4 and there has to be 4 times as much output torque during the push.

Yes when the output is stoped there is no output power or torque just like in a PWM. However, since there are four sets of levers the output shaft is never stoped since there is always one set of levers pushing on it.

Re: Interesting speed reducer mechanism
 

As per the bullet points above the animation, the mechanism "delivers constant torque throughout the speed range." It doesn't increase torque as speed decreases because the output shaft's angular velocity is equal to the input when it is turning -- assuming they're of equal diameter. It's output is intermittent. Glancing at the animation suggests that arrangement rotates the output about 30* per control arm cam per input revolution. Four control arm cams, then, rotate the output 120* per input revolution; a reduction of 1:3. Adding more control arm cams or changing the geometry of the existing cams can vary this ratio. For the 2/3 of each input revolution that the output is not moving, the energy is being lost to friction (heat) within the one-way bearings.

Presumably, the attached lever has some role in adjusting the control arm cam geometry and varying the output speed as a result, but how it does so isn't clear from the animation.

Re: Interesting speed reducer mechanism
 

Definitely interesting...

Although, for robotics applications (not necessarily industrial) the downsides of it definitely outweigh the advantages. However, I can see the benefit of such a device in industry (After using a similar, much larger version for a fixture this summer).

It'd be nice if we had an explanation from an engineer who 100% knows how it works.

Re: Interesting speed reducer mechanism
 

As Qbranch pointed out, this thing is a system of levers and clutches. By moving the fulcrum, the user adjusts the lever ratio and thereby swaps speed for torque. The manufacturer's "constant torque" spec refers to a safe operating area (SOA).

My boss, whose current title is VP Engineering, recalls specifying one of these units for a factory machine about 40 years ago, when he was a co-op. So it seems these have been around for quite a while. They must work well in some applications. But I don't think FRC robots would be one of them.

Re: Interesting speed reducer mechanism
 

I wouldn't be surprised if that thing (or a predecessor) was patented 100 or more years ago. Must be many steam-powered machines that have some such mechanism.

I can see this concept being useful to ratchet out a robot appendage or perform some similar task.

I did see a site with a laboratory stirring mechanism that uses this same reducer.

Re: Interesting speed reducer mechanism
 

See that doesn't seem right. I don't think the lever distance has anything to do with swapping speed for torque but rather the frequency at which the shaft is engaged or disengaged. If this frequency is increased (by moving the lever farther back and forth) then we get higher RPM but the torque still remains the same.

Essentially all this really is is a fancy clutch mechanism.... it engages and disengages the output at different frequencies resulting in different speeds. However this does not change the torque characteristics of the system because during the time that the shaft IS engaged the motor is still in the same state had we just connected it directly to the output shaft.

I don't see the practical advantage over a traditional gear box, perhaps less motor load (because you allow the motor to free spin between cycles)
well... of course the fact that it is continuously variable

Re: Interesting speed reducer mechanism
 

Exactly what i've been trying to say!

-q