## Simulating Ratchet Mechanism

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Lance21
Posts: 2
Joined: 25 Jun 2020, 02:32

### Simulating Ratchet Mechanism

Hello, I am trying to simulate a robot that has a ratchet mechanism (which will allow the joint and robot to rotate clockwise, but restrict rotation in the counterclockwise direction). I was wondering how I could achieve this using CoppeliaSim as I am a fairly new user. Is there a feature that restricts passive joint rotation in one direction? If not how exactly could I accomplish this?

fferri
Posts: 627
Joined: 09 Sep 2013, 19:28

### Re: Simulating Ratchet Mechanism

Hi,

maybe you can do that with a Joint callback function.

Lance21
Posts: 2
Joined: 25 Jun 2020, 02:32

### Re: Simulating Ratchet Mechanism

So I was thinking of achieving this using sim.getjointForce to check if the torque applied to the joint was positive or negative. And if it is negative then write a zero velocity to the joint to restrict it from moving in the opposite direction. I do not require specific position control from the joint that the joint callback provides. Would you recommend implementing this method in the joint callback function within the joint child script or writing it in the main robot control script?

Thank you

coppelia
Posts: 7928
Joined: 14 Dec 2012, 00:25

### Re: Simulating Ratchet Mechanism

Hello,

I would put that inside of a joint callback function, inside of a child script attached to that joint. And don't check the torque applied to it, but the movement direction instead. Something like:

Code: Select all

function sysCall_init()
jointHandle=sim.getObjectHandle('joint')
lastPos=sim.getJointPosition(jointHandle)
end

function sysCall_jointCallback(inData)
dx=inData.currentPos-lastPos
dx=math.atan2(math.sin(dx),math.cos(dx))
lastPos=inData.currentPos
local outData={}
outData.velocity=0
if dx<0 then
outData.force=0
else
outData.force=10
end
return outData
end
Make sure that your joint is dynamically enabled, the motor is enabled, and the control loop is enabled too (and you are in position control).

Cheers