"slider-crank"-style lift mechanism. What workaround to avoid dead point/singularity?

I realize it is a bit difficult to see, but the fact that the platform is constrained side to side, as the front and/or back motors turn at the linkage point the blue link is forced to rotate the same as the orange link. You may have to set it up with the side to side constraints to see what I am talking about. The blue will rotate by virtue of the motor moving the orange relatively.
As for gearing that can remain also. Just keep the motor fixed to the blue link and drive the orange link at the pivot point connecting blue to orange. You can put whatever you want for gearing between motor and orange link drive shaft.
Jeff


thorq said:
Yes Jeff I already have a constrained vertical motion with 3 cranks, there are the two points I am worried about: one is when the arms become co-linear and the second is play, which will happen how ever tight the rotary joints are. Oh and the length of the arms should be equal so they pass one another, the image is from a version where I kind of settled with the limited-range solution.

I get that putting the motors at the elbow of the rotating arms would actually make the singularity a non-issue and that's a very good suggestion but how is the blue arm going to rotate around its own axis. I think I am missing something here.

Now, the problem is that I am using the large blue wheels as a gearing down mechanism to get some precision from the stepper motors. I would be more than happy to be able to use cycloid gearboxes but that is not an option so my idea is to gear it down via an at least 8:1 gear and pinion approach.

I wonder if I would use a 2 stage transmission, where I would gear down at only one crank and use a timing belt to serially rotate all other elbows as if the motors would be there... this might work. I'll have to think a bit about this, it's just an un-edited thought.
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What I mean by side to side constraints is just if you don't want to put the side linkages on right away and want to experiment. Once you have your side linkages on, they will serve as the side constraints.
 
Hmmm, I fail to see what you are saying :(. But if it is dependent on 2 motors then I have to say again that I designed this for light duty stuff so I have envisioned a single motor engaging the blue wheels in series via cable drive or synchromesh. I could up the number to two motors but I it would be quite difficult to put motor on a circular orbit around the blue wheel radius because of size constraints.

I am open though to further discussing it but I wish I could visualize your idea. Moreover i can't see how i can maintain gearing down via the difference in size between the motor pulley and the blue wheel and still rotating the orange arm at the geared down speed.

You have totally confused me :)
 
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If the blue wheels are the gear down, you are going to have to make sure the belt cannot slip from one link to the next. If you want 1 motor total with blue wheel gear down, put the blue wheels on the orange link pin joint, run the tootheed belt round the entire system looping around every blue wheel and use a spring tensioner to take up the slack as the blue wheels orbit around the blue link anchor point, which is where your drive point used to be.


thorq said:
Hmmm, I fail to see what you are saying :(. But if it is dependent on 2 motors then I have to say again that I designed this for light duty stuff so I have envisioned a single motor engaging the blue wheels in series via cable drive or synchromesh. I could up the number to two motors but I it would be quite difficult to put motor on a circular orbit around the blue wheel radius because of size constraints.

I am open though to further discussing it but I wish I could visualize your idea. Moreover i can't see how i can maintain gearing down via the difference in size between the motor pulley and the blue wheel and still rotating the orange arm at the geared down speed.

You have totally confused me :)
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If the blue wheels are too big to orbit, gear down first, which is likely a better option anyway. Gear down from motor to primary drive pulley, then take a second belt off the geared down shaft and thread it through the linkage system.

Jefflucasart said:
If the blue wheels are the gear down, you are going to have to make sure the belt cannot slip from one link to the next. If you want 1 motor total with blue wheel gear down, put the blue wheels on the orange link pin joint, run the tootheed belt round the entire system looping around every blue wheel and use a spring tensioner to take up the slack as the blue wheels orbit around the blue link anchor point, which is where your drive point used to be.
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This would bring me very close to the video in my second post in this thread, which uses a belt to have the arm origin rotate in tandem with the crank origin to avoid dead spots. (and as a side note isn't this solution patented? maybe it already expired)

With belts that solution would most likely work although threading the belt is more of a challenge than threading cable. Maybe synchromesh is a better alternative but simple cable is very difficult in this case.
 
Thorq,
I have been racking my brain for different applications that would make my linear linkage an exclusive best mechanism, but alas I am not so sure that there are any applications that just can't live without it. In short, here you go; it is now public domain:
https://www.youtube.com/watch?v=6iLu__COq4w
Perhaps you will find it useful in your application.
 
That is a strange and complex mechanism :-o . It does the job but the range is quite short for how long the links are.
Man I wonder how can a brain come up with such intricate mechanics. It's so cool watching it in a loop almost hypnotizing.

I am afraid this is way too complex for my application too :(( which is a pity cause I almost gave up searching something simpler than having the belt rotate the arm origin in tandem with the crank origin). For me that is the simplest because it needs fewer components and I need anyway 3 or four of them to balance a large platform.

In my situation I have to have the big blue gear at the origin of the crank in order to be able to thread the cable through all the cranks and use one single motor. I will have a better sketch foe everybody to see what I am talking about.
 
All agreed. I thought your initial chained/tooth belted discovery was the right solution. But, when you said you wanted to eliminate gears I took off down a different road.
Hope you see that you want to keep the non-orbiting sprocket fixed and 2x as big as the orbiting sprocket. Also note that this is a geared linear linkage, you would not need to constrain the side to side movement; you could just have the devices on two opposite sides, not 3 or 4 sides.



thorq said:
That is a strange and complex mechanism :-o . It does the job but the range is quite short for how long the links are.
Man I wonder how can a brain come up with such intricate mechanics. It's so cool watching it in a loop almost hypnotizing.

I am afraid this is way too complex for my application too :(( which is a pity cause I almost gave up searching something simpler than having the belt rotate the arm origin in tandem with the crank origin). For me that is the simplest because it needs fewer components and I need anyway 3 or four of them to balance a large platform.

In my situation I have to have the big blue gear at the origin of the crank in order to be able to thread the cable through all the cranks and use one single motor. I will have a better sketch foe everybody to see what I am talking about.
Click to expand...
 
I other words, drive the blue wheel directly, and keep the big sprocket locked (not rotating). Then the farthest point stays in a straight line without needing any constraints or rails.
 
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