Rack and Pinion problem

[pepper99]

Hi!

I'm building a servo-based robotarm as a school project and ran into a problem while building my last part (claw/end effector). I'm going to use a rack and pinion mechanism for the claw, where two racks facing opposite directions are placed onto the pinion gear. When the servo rotates (170 degrees max) the racks are going to be pushed apart or drawn closer. Thus if I one rack moves 5 cm, the distance between the jaws will be 10 cm. 

I have calculated the size of the pitch circle diameter of the pinion gear according to the arc length formula (since only 170/360 degrees of the pinion gears circumference will be moving the rack when the servo rotates) but I can't make it work with the spur gear component generator. Whenever I get the pitch diameter to the right size ( Module*Number of theeth = pitch circle diameter) it displays design failure. 

Any help is greatly appreciated.

Cheers

[johnsonshiue]

Hi! It is possible there is a flaw in the design (or parameters) or there is a bug in the software itself. Without the files (iam and ipt files), it is impossible to tell. Please use Pack and Go to find all the related files (iam and ipt) and attach a zip file here.

Many thanks!

[pepper99]

Hi again!

The parts in the assembly are not complete, and the cog ontop of the servo was only placed there to illustrate its purpose. If you edit the cog in the design accelerator you will see that there is a design failure. The pitch circle diameter is supposed to be 34 mm for gear 1. I chose "no model" for gear 2 as I will use a rack instead. Hope this gives some insight to the problem.

[jhackney1972]

Your design entry parameters are at fault.  You have elected to have gear calculations on, you have specified a gear/rack with a width of 10 mm and you have specified the system must transmit 1.0 kW of power.  The gear/rack system cannot transmit that amount of power so you have a failure!  You have three choices, turn off the calculation (see screen capture below, red arrow), change the power being transmitted or change the width of the gear/rank system or a combination of all of them.  I contend that you probably cannot buy a spur gear that narrow anyway.  Searching on the Musumi site, the minimum width of a spur gear with 17 teeth is 20 mm.  This width still will not handle 1.0 kW of power.  If you want to leave the width of the system at 10 mm, the approx. maximum power it can transmit is 0.35 kW.  Plug that value is your current Inventor calculations and you will get an acceptable solution.  See first screen shot.

[WHolzwarth]

This is a frequently issue in Gear Generator. The initial default Power settings are too much for small gears.

Try that:

- In Spur Gear calculation sheet, change power to 0.01 kW

- In Design sheet, change unit Correction of Gear 2 to zero.

After these changes it should be ok.

[JDMather]

Will you be 3D printing the gears?

[pepper99]

Hi!

Looks like I didn't look through the calculation tab carefully enough. Thanks alot for the help. 

Have a great day!

[pepper99]

Hi! 

Yes I will be 3d printing the the whole thing including the gears (when it's done).

[pepper99]

I will make sure to try those changes. Thanks!

[JDMather]

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@pepper99 wrote:

Hi! 

Yes I will be 3d printing the the whole thing including the gears (when it's done).

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The Gear Generator creates simplified gears with teeth that interfere - you will want to Right click on the Spur Gears node and select Export Tooth Shape to set appropriate backlash (clearance) for your printing process and pattern the tooth for a smooth running geatset.