Compound gear meshing trouble with rack

AnupSebas10 · Apr 22, 2020

I'm new to the forum. I was designing a beating mechanism which consists of 2 arms hitting a variable diameter stem of a plant. These arms are pulled back by the driving gear(s) and when released, slides with the spring force and hits the stem. When the driving gear reengages with the rack to pull it back and get ready for the next hit, there is a problem in meshing, the two teeth's top faces can hit each other and damage itself.
Is there any way to ensure proper engagement as the rack can be anywhere when the pinion engages?
Some design constraints:
1. Very limited space
2. One motor drives everything
3. no space on both sides of the gear.
4. No heavy loads (<2kg)
5. Motor rpm will be around 60rpm

Gear A drives gear B or vice versa. Both these gears drive 2 racks on either side of the gears. These racks are the beating arm which is spring-loaded. Do not mind the sprigs ends, it only for showing the spring position. The dimensions of the outer boundary are close to 220mm x 120mm

btrueblood · Apr 22, 2020

You will always have a problem getting the gears to re-engage with that mechanism, and I'd expect the leading tooth to wear away severely within a few hundred strokes, regardless of the material of construction. Why not simply power the shafts through an electric clutch, which disengages to allow the springs to whack whatever they are going to whack. Or cut power to the motor at the end of the stroke (though that means the springs have to be heavy enough to overcome motor inertia and friction).

AnupSebas10 · Apr 23, 2020

I have to check out the clutch mechanism how it works and what are the main parts. How efficient and lasting are the clutch mechanisms? Also, The design constraints are crucial, I have to drive the mechanism with one motor in limited space. I found something on the internet which minimizes the damage on the teeth.
Check the link:

https://robomechjournal.springeropen.com/articles/10.1186/s40648-017-0084-4

The problem with switch on and off the motor is that the energy consumption will be high. I asked this to a electronics guy about this. The starting power is higher. The mechanism needs to continuously run for 3 minutes in one go which would drain the battery. Cutting the power was a great idea but the mechanism has a default open position. I use a worm gear motor to stop lock the mechanism when the power cuts off. The worm gear motor cannot rotate back under spring tension.

mfgenggear · Apr 23, 2020

So I tried to brain storm this issue, and I agree with BTrueBlood,
it seems to me also some type of clutch to engage and disengage.
to allow it to free wheel.
or maybe use a crank style mechanism.

AnupSebas10 · Apr 24, 2020

Sure, I am already looking into it. Crank style mechanism I'm trying if it works for my use.

Windward · Apr 28, 2020

I haven't tried to find a solution to your problem, but I have a suggestion I think would be valuable for all engineers. Search for "Mechanisms and Mechanical Devices Sourcebook." You will find free versions of the latest edition [5th] of this mighty work, nearly 600 pages of every kind of mechanism that has ever been invented. You might find something there to fix your problem.

I don't understand why this book is free on the internet, but there it is. Even a printed copy is available for very little money, $15-$30. This is an astounding bargain, which you will see if you didn't know about that book.

Nick Chironis got it going back in the 1960s. He is no longer with us. Maybe he wouldn't mind that this book is free to all. He was that kind of guy.

3DDave · Apr 29, 2020

It appears the copyright is held by "The McGraw-Hill Companies". I expect the "free" copies are from places that play whack-a-mole with the copyright lawyers. Apparently that is how Scribd operates.

Windward · Apr 29, 2020

I was afraid of that. I wonder why anyone would go to the trouble of stealing a protected work and then publish it without conditions. There is no advertising with the free book, just the full text in PDF. I feel guilty now, will buy the book.

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