please help me with wiper geometry

[ari666]

hi all. im struggling (again) this time its with wiper geometry. the drivers side wiper goes too far, i need it to go about 90 degrees in an arc and its going more like 100 degrees, which then carries it over the edge of the window and scratches the A pillar

so far i have moved the pivot points on both sides of the connecting rod, in the hope that there would be less travel. but, it seems i may have actually increased it... is that possible? could someone please help me figure out what i need to make the drivers side move THE EXACT SAME AMOUNT AS THE PASSENGER?

fire off questions, ill be round
thanks

edit* its not really clear on my pic, but the motor (center thingie in the pic) spins round 360 degrees and pull/pushes the LHS arm, the LHS in the arm moves 90 degrees and then the connecting rod somehow makes the RHS move 100 ish degrees. the wipers connect to the BASE of the RHS and LHS arms.

[ari666]

[some_guy]

Just did a quick geometry diagram on my work pc to check I was right. To decrease the wiper blade spread you need to increase the length of the arm the connects the left wiper to the right wiper. So basically the opposite of what you have done which should net you and opposite result. I hope I made sense.

[ari666]

yep, just tried it and it works! now, if someone could just go ahead and explain the math behind that, that'd be great cos' im pretty sure my brain just broke.

basically: by shortening the driving arms distance from pivot to pivot it reduces the degrees of travel, but reducing the recievers arm it lengthens the travel... ???

[some_guy]

Becasue you have now increased the receivers arm length, you have lengthened the radius of the arc that the pivot point (point of intersection of the receiver and driving arm) follows. And without exponentially increasing the length of the drive arm, the pivot point cant travel as far as before. meaning that the wiper rotates less.

Again, i hope i made sense.

[ari666]

lol [scruntchy face] ok man.

[some_guy]

I can explain it in more detail if you like?

[some_guy]

I drew my own diagram

The bottom set is the step 1 the top 2 are after a quarter rotation of the motors full spin.

So as you can see by changing the mounting point in the topmost view the wiper has pulled further than the middle view.

I hope drawing that helped.

[ari666]

totally! i cant give you more rep tho pooter says i need to spread it round more