Gears Problem

tom_gullan

Hello,

Can anyone point me in the direction to a solution for my gears problem?

I am trying to assemble crankshaft and camshaft gears so that the crankshaft turns the camshaft. I have read lots of articles on this subject but, so far, the answer has eluded me. Using the respective revolutes, I can get each shaft to rotate independently. However, when I try to setup a Gear Relation and use the crankshaft rovolute, the gears do not turn together.

Any help would be gratefully appreciated.

https://cad.onshape.com/documents/be47b9c94cde49171681bc0b/w/f4123ba9e380434b1beaaf3b/e/4ef366bc242e1419a4110d9b

Regards
Tom

NeilCooke

Set your gear ratio to 0.5

tom_gullan

Good evening Neil,

Thank you for responding. I have tried this but it does not seem to work.  

When I animate the Crankshaft Revolute, the crankshaft turns but its gear does not. At the same time the camshaft gear turns but its shaft does not.

Do you have any other suggestions?

Regards
Tom

john_mcclary

Your cam gear should be fastened to your cam shaft. It looks like both your cam shaft and gear are independently mated to the gearbox wall with revolute mates. So they are free to move independently of each other 

matthew_stacy

Yeah, what @john_mcclary said!  I probably should have read that before jumping into the document. 

You can suppress or delete that revolute mate between camshaft-gear and wall.  Apply a FASTENED mate between the camshaft-gear and the camshaft.  Then apply a gear relation between crankshaft and camshaft (0.5:1 ratio, play with direction and/or reciprocals till it works right).

https://cad.onshape.com/documents/e485eb4a808db8cf2348ffd2/w/b642ca7adcb3a6e8507f99ae/e/38fba5fcdf1c6733767bf947

(Workspace B, V2)

tom_gullan

John, Matthew,

Thank you very much for all your help. 

I know a bit about fabricating model engines from bar stock but I'm a total novice when it comes to CAD. This has been a very steep learning curve for me. 

Mating the camshaft gear to the engine casing was an error which I know was wrong but couldn't see the wood for the trees. What really confused me was that I tried to configure the Gear Revolution with the gears and not the shafts.

Once again, thank you for all your help.

Kind Regards
Tom

matthew_stacy

@tom_gullan ,

It took longer than I care to admit to embrace Onshape's mate schema. Very different than SolidWorks. But I'm getting there. Keep at it. That is a very cool model that you are working on.

tom_gullan

Matthew,

I've hit two more problems. Can you help?

1. I have used the same fasten mate to secure the second cam to the camshaft but it will not rotate when I use the camshaft revolute.

2. When I use the camshaft revolute to animate the engine, apart from the second cam not turning, everything else seems to work fine. However, if I use the crankshafts revolute, the camshaft appears to only rotate 180 degrees then reset itself.

https://cad.onshape.com/documents/b1097b3cdc5f46f3e36bf722/w/1d4b15b35bcd41833649067d/e/0e596987b72c16d226793cd4

Regards
Tom

Prachi

The animate of crank shaft setting is 'reciprocate'. Change to 'loop' and it works fine as your expecting.

matthew_stacy

@tom_gullan both cams seem to be rotating properly with the camshaft. I didn't make any changes there. But as @glen_dewsbury suggested, selecting the 'playback type' to 'Loop' we keep the rotation moving in the correct direction. However it should be noted that you need to rotate through an entire cycle for a smooth animation. If you animate the crankshaft from 0 to 360 degrees and then loop, you will observe that the camshaft (and cams) instantly skip half a revolution. The crankshaft should be looping from 0 to 720 degrees.

If you haven't yet run through the Branching & Merging lesson in the learning center yet, I highly recommend it: https://learn.onshape.com/courses/fundamentals-branching-and-merging. Might just blow your mind. Anytime that you're contemplating making a risky design change (mucking about with mates in a complex assembly for example) just create a VERSION and then BRANCH off of that version to create a new workspace. That way you can recovery gracefully to the original design condition if things go sideways. I promise that lesson will be an evening well spent.

The tangent mates for your pushrods seemed a little goofy. I believe you'll be better off mating to the end FACE of the pushrod, rather than the EDGE. Note that there is an icon in the lower-left-corner of that mate dialog box to 'Reverse Primary Direction' of the mate if you are getting an error.

I copied your document, versioned it, and then branched off into a new workspace (B1) to play with the pushrod tangent mates. But note that your original is still there. You can toggle back and forth between the MAIN and B1 workspaces.

This is a really cool project that you've undertaken. Nice work!

tom_gullan

Matthew,

Once again thank for the detailed feedback.... I really appreciate the help.

Regards
Tom