Recommendations on getting started with VREP/Arduino

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coppelia
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Re: Recommendations on getting started with VREP/Arduino

Post by coppelia » 15 Apr 2016, 08:27

Your kinematic chain doesn't contain a single joint. How do you want IK to work properly? Did you even read the IK tutorial or the related documentation?

Cheers

dnahar
Posts: 30
Joined: 07 Jan 2016, 03:03

Re: Recommendations on getting started with VREP/Arduino

Post by dnahar » 19 Apr 2016, 16:33

Thanks for the information. Actually, our real robot is a continuum robot, do not have rigid joints. But, i have changed the simulation to as mentioned and we are going ahead with that. There is one more very important feature in our real robot that we have to give the simulation in vrep:

Our middle and distal(end or proximal) section contracts in the real robot, could you give me an idea how can i add this feature in the simulation in vrep?

https://www.dropbox.com/s/k4tihb59nnz9o ... l.ttt?dl=0

Thanks,
Dixit

coppelia
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Re: Recommendations on getting started with VREP/Arduino

Post by coppelia » 20 Apr 2016, 10:48

Ok, that is already better. Your IK is working. You might have to add a bit more of damping, since when your targets are far out of reach, things can get less stable.

If you need a special behaviour at some joint locations, you have several possibilities:

1. You could simply set the joint angle to a specific angle.
2. You can also combine 1 by locking the joint afterwards for IK (i.e. it will be ignored by IK). For that, you can change the joint mode to passive instead of IK (simSetJointMode)
3. You can build-in additional, local IK constraints, which can force a joint to prefer a contracted state for instance.
4. With revolute joints, you can also have joints in dependent mode. This means that those joints will be linked to other joints via a linear equation.
5. You can programmatically move the IK targets in order to bring the robot in a desired configuration.

Cheers

dnahar
Posts: 30
Joined: 07 Jan 2016, 03:03

Re: Recommendations on getting started with VREP/Arduino

Post by dnahar » 30 Apr 2016, 22:41

Hello,

Still, i do not know how to go ahead with my requirement. If you look at the above model, the model is currently of full length, i want the model to contract between dummy 4 and dummy 6, dummy 2 and dummy 4. Ideally, the joints should come closer to each other and cylindrical shape between them should contract. Please let me know if this can be achieved.

If not, then when i want the model to contract, i am thinking of a possibility of deleting one joint and one cylinder, then proximal to this deleted shapes, the joints and cylinders should come in IK mode with previous(parent to deleted shapes) joints and cylinders resulting in decrease of total length, leading to contraction.

Let me know if this is achievable.

Thanks,
Dixit Nahar

coppelia
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Re: Recommendations on getting started with VREP/Arduino

Post by coppelia » 02 May 2016, 08:44

You can also add some prismatic joints, if you need contraction, like a telescopic mechanism.

You have to remember that you can't do everything with IK. You can adjust many parameters so that the mechanism starts behaving as you want, but for that you need to have a very good understanding of IK. IK will not magically do what you want.

Since you have a long kinematic chain, try first with a much shorter chain, adding different types of joints, constraints, and experimenting a bit. Only once you are able to reproduce the desired behaviour, can you combine several behaviours and finally reach what you want.

Cheers

dnahar
Posts: 30
Joined: 07 Jan 2016, 03:03

Re: Recommendations on getting started with VREP/Arduino

Post by dnahar » 10 May 2016, 00:53

Hello,

https://www.dropbox.com/s/qbbdddlenac2x ... t.ttt?dl=0

I want to have contraction in below model using prismatic joints which i am testing using above model. I have developed a small kinematic chain for that(above). I have few problems with that:
Could you tell me why i am not able to move it during running. I am trying to move in z direction only to use the prismatic joint.
Also, to the blue colour cylinder(above model) i visualize of adding spherical joints to the end to achieve bending as in below model and continue doing that to make 1 complete model. Is this possible? or how should i go ahead with this?

https://www.dropbox.com/s/k4tihb59nnz9o ... l.ttt?dl=0

All your help is appreciated.

Thanks,
Dixit

coppelia
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Re: Recommendations on getting started with VREP/Arduino

Post by coppelia » 10 May 2016, 08:54

Your first model has following problems:
  • Your have a 1 DoF mechanism, but specify 6 constraints (x/y/z/alpha/beta/gamma). Keep only the Z constraint. Or use the DLS damped solver, and set a relatively large damping factor (e.g. 0.1 or 1)
  • Your joint has range zero: it will not be able to move at all!
  • Your IK element is not active (check the Element is active checkbox)
Your second model also has too many constraints set too. The orientational constraints are not needed in your case (I guess). But there at least, you are using the DLS solver.

Cheers

dnahar
Posts: 30
Joined: 07 Jan 2016, 03:03

Re: Recommendations on getting started with VREP/Arduino

Post by dnahar » 13 May 2016, 00:28

Hello,

Thanks for the suggestions. It seems i have completed the simulation. The model looks capable of bending and contraction. Please have a look at it.
Now, our next step is naturally, to map the movements of real and virtual robot. The real robot is highly nonlinear in bending and the curves it can take, on different actuations. Could you suggest me, what should i look at from what v-rep has provided on motion planning, position planning or all related topics on how to map real robot(actuations and position) and virtual robot(positions) movements?
https://www.dropbox.com/s/125w6or15mpiv ... F.ttt?dl=0

Thanks,
Dixit

coppelia
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Re: Recommendations on getting started with VREP/Arduino

Post by coppelia » 13 May 2016, 14:07

Dixit, your robot is very specific and we can only support you up to a certain point, since we lack knowledge of what exactly you want to do, what algorithms you want to use, what the real robot looks like. At the same time, we cannot spend hours in looking at people's scenes and code and solve their problems, otherwise we would only be doing that. We are here to answer precise questions related to V-REP, but the algorithms you want to use have to be developed by yourself.

Cheers

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