Robotics 1 U1 (Kinematics) S5 (HTM) P3 (Denavit Hartenberg Examples)

[@Enidable]

Thank you for your great lectures! You've saved me so much time and frustration with your skills and generosity!

[@carbon273]

For the last question, The alpha value in the second row should be -90 not 90 degrees if you follow your definition for that parameter for DHM. If you rotate the previous frame, frame 1 relative to the x axis at frame 2 so that the z axis lines up, you will get -90 or 270 degrees. If possible can you enlighten me if I am misinterpreting the process. I have gotten everyone of these correct on my own besides that one.

[@asodemann3]

First, make sure you are using your right hand. Now, point your thumb in the direction of X2, which is pointing away from you (into the screen). Now, put your fingers pointing in the direction of Z1 (up). The palm of your hand should now be pointing to the right. Now, look at the direction that your fingers curl in this position - they curl down to your right. Z2 is pointing to the right, so we want to rotate Z1 90 degrees in the same direction that our fingers are curling in order to get it to match Z2. That's why the alpha parameter is a positive 90 - because we want to rotate the axis in the SAME direction our fingers are curling.

[@ismailkarnanokung4753]

Thank you so much, I like your videos , they all very instructive

[@gazzamgazzam4371]

Thank you for your explanaition, could you please give us the examlpes in a sheet of paper (word or pdf format)?

[@Blargmaster-pf4bf]

thanks lady for the finals cram material

[@poke_champ]

rotating clockwise should be -90 degrees

[@zv3495]

yes?

[@MegaSuscribe]

left rotation is mathematically positive rotation so yes you are correct

[@natnaelasmare3263]

the frame to be rotated is the n-1 frame not n

[@ansonpaul2538]

how to join your robotics course what is the 8 digit id code they were asking while registering?

[@muhammedmacit7191]

mrs. sodemann how did you write the second joint's TETA parameter which we rotated to counter clockwise, therefore ı think it should be -90

[@griouimohammedamine205]

yes I agree with you alpha is -90

[@isagumus1]

It depends on your notation. It could have been written like that either does not matter.

[@nemanjatrivic9505]

@@isagumus1 Yes it does matter 90 does not equal -90. Because -90 = 270.

[@jaiprathapgv2273]

Mam that doubt is u have to rotate the X1 to X2 in clockwise so the theta2 should be -90 degrees?

[@asodemann3]

When you are thinking about whether the rotation is clockwise or not, make sure you are looking at the frame from a perspective where the Z axis is pointing towards your eyes. If you look at the frame from the other side, you will get 'clockwise' backwards.

[@jeromeblacq7528]

Please, how can I apply this in a planar situation

[@drummytbone23]

Hi at 4:00 I was wondering why the theta value is positive 90 when you are going clockwise rotating around z1 so x1 will line up with x2.

[@asodemann3]

Z1 is going away from you (into the screen). Using your right hand, point your thumb in the direction of Z1. Now, look at the direction your fingers curl - they curl to your right. That is the same direction you have to rotate X1 to get it to match X2; that's why the theta value is positive.

[@tomahan044]

I was quite sure you were wrong but damn I was wrong

[@meeranalikhan2199]

@@asodemann3 You are absolutely to the point I appreciate that.

[@Amoetodio04]

Great videos! Thanks for sharing!

[@oleksandrvdovychenko7294]

Awesome!

[@narayandharwadkar9616]

Thank u for ur video mam. But I'm bit confused at 20:42 that why should we place 2 frames with their centres at same exact location.....only in spherical robot but not in scara and articulated robot pls can u explain... waiting for ur reply ...

[@TranThanh-ip9rq]

thank you so much

[@eudo81]

in this video "2 2 1 Lecture Video 2 of 6 Jacobian Matrix Explanation" you have the same manipulator to calculate the homogeneous matrix but the result of H12 about distance[x,y,z] is different than here. With denavit-harterberg method d=[0,0,0] and your calculations there ared=[a2cΘ2,α2sθ2,0]. could you explain why?

[@thetrippydeer8574]

but you don t need to sum with a cause d already counts the a distance

[@burakdemir1801]

The question after 29 minutes and 35 seconds is the same as my question. and how do I fill in the form of alpha i, alpha i, d i, qi when I fill in the DH table. I filled it with alpha i = (0,0,0), alpha i = (0, -90,0), di = (0.3, d2, d3), Qi = (Q1,0,0). Would you write your e-mail or did I go wrong?

[@user-wm8xr4bz3b]

sorry, can i check at 22:32, theta2 should rotate around z1 or x1 ?

[@asodemann3]

You're right! I should have said Theta 2 is rotation around Z1, not X1

[@Absolumify]

For the second example (spherical one I think), the D-H rules were referenced and as such the third frame placed on the second frame. So from my understanding Xn must be perpendicular to Zn and Zn-1 as well as intersect both Zn and Zn-1. So my question is, why move the frame to be on top of frame 2. If the frame stayed where it was, would it not satisfy the rules anyway?

[@Absolumify]

Never mind, I figured it out. Was just mixing up the Z1 axis orientation.

[@asodemann3]

You can go back to the frames video via this link: kzbin.info/www/bejne/q6WXpo1sjt-pbNE Or, you can go to my website www.robogrok.com and go to the Robotics 2 course, and click on 'Denavit-Hartenberg Forward Kinematics'.

[@Abhilash-.]

I cannot see the challenges and projects in the two courses , could you please make them available.I am trying to do projects really similar to those.

[@asodemann3]

Abhilash V J I am not sure what you mean by saying that you 'cannot see' them. The challenges are the hands-on part of the videos. If you can see the videos, you can see the challenges, too.

[@syedmuhammadmusab554]

Hi! In the case of determining the value of @ALPHA@ which frame do we need to consider for (x rotation to match zn-1 to zn ) frame n-1 or frame n. because you are using both of them in each example.

[@LololeoLolo]

rotate frame n-1 using xn . so you identify xn , but you rotate frame n-1 using xn .

[@AK47dev1_YT]

Charming!

[@burakayan3360]

mam first of all. i again thank you for the video. and i would like to ask a question. i have assigned the x0 axis as if towards up, and i contuniued my calculations. however i couldn't find the right answer. so, in DH table, i regarded Q1 (theta 1) as 0 because in my kinematic diagram there was no rotation. am i wrong to do so ? i mean, i thought that we had a complete freedom while choosing the direction of X0 as long as it is perpendicular to Z0 axis. i hope i explained my problem. thank you for the answer.

[@haroonjavaid3918]

Respected Madam last example which started at 31:30 in video...

[@haroonjavaid3918]

Respected Angels Sodemann whenever you talk about frame?? What does it mean?? Frame?? (So i need to ask myself how would i rotate the frame n-1 frame around the axis zn in order to get z(n-1) to match with zn) what is the frame??

[@asodemann3]

The word 'frame' is short for 'coordinate frame', 'frame of reference', or 'reference frame'. These all mean the same thing in this context. They refer to a single set of X, Y, Z axes that 'go together' - they are mutually perpendicular, they have the same origin, and the follow the right-hand rule. For example, in the first example in this video, there are four frames numbered 0-3 and drawn in a red color. When I say that we 'rotate the frame', it means that the center of the frame will stay in the same location, but the directions of the axes will move. However, since we are rotating the whole frame, we need to move the axes in such a way that the axes maintain mutual perpendicularity and the right-hand rule. So, still using example 1 in the video at time 00:00, suppose that we are going to 'rotate frame 0 90 degrees around Y0'. This operation would leave Y0 as it is, and would make Z0 point into the page and X0 point to the left. The center of the frame would remain where it is, at the center of the first joint.

[@bergamobobson9649]

please got a question why theta for the row 2 is not 180 instead of 90 am not getting that part...i was thinking that maybe we've to a double rotation to get the axes x1 and x2 to match Thanks

[@asodemann3]

Which example in this video are you asking about?

[@bergamobobson9649]

Angela Sodemann the First One Madame, and also also the Alpha of the second row(First e.g aswell i did not get It) Thanks

[@asodemann3]

Theta in the second row is the amount that we have to rotate frame 1 around Z1 in order to get X1 to match X2. In the diagram, X1 is pointing up, and X2 is pointing to the right. The directions 'up' and 'right' are 90 degrees apart from each other. In other words, draw a dot on a piece of paper. From that dot, draw one line going 'up', and another line going 'right'. These two lines will meet at the dot at a 90-degree angle. If we would hold on to the axis Z1 and rotate the frame 1 90 degrees to the right, X1 would then be pointing to the right. In order for two axes to be 180 degrees apart, they have to be opposite directions. For example, if one axis is pointing 'up' and another is pointing 'down', or one axis is pointing 'right' and another 'left', those axes are 180 degrees apart. So, X1 and X2 are NOT 180 degrees apart from each other, because they are NOT opposite directions. Alpha in the second row is the amount that we have to rotate frame 1 around the axis X2 in order to get Z1 to match Z2. Z1 is pointing into the page (away from us), and Z2 is pointing down. The directions 'away from us' and 'down' are 90 degrees apart; the two lines meet at a right angle. So, we know that the angle for alpha has to be 90 degrees. But, now we have to decide if the direction should be positive or negative. Using your right hand, make a fist with your thumb sticking up (a 'thumbs-up' gesture). Put your thumb in the X2 direction (pointing to the right) and look at the direction your fingers curl. If we would rotate Z1 90 degrees in the same direction that your fingers are curling, Z1 would point up. But, we don't want Z1 to point up, we want it to point down to match the direction of Z2. So, that's why alpha in row 2 is negative - we want to rotate Z1 AGAINST the direction of your finger curl.

[@bergamobobson9649]

Thanks a lot madame all things become clear now...Thank very much

[@harshprajapati6327]

at 8:08, Can I write +270 (positive) instead of -90(minus 90)?

[@hariprasanth9456]

you cannot... bcoz if the joint 2 rotates +270, joint 1 and joint 3 will collide..

[@haroonjavaid3918]

Madam thank you so much...Madam do you have more examples then please tell me..i mean to say not to solve the example so that i will do practice again and again...I shall be very thankful to you for this act of kindness...

[@vilva15]

Hi, Thank you for teaching robotics. You've made the concepts so much clearer. There is a problem that I was hoping you could help me solve. It's a spherical wrist of the PUMA robot. Is there an e-mail address I can send it to you at?

[@yashpamnani5391]

α2(alpha 2) should be -90 degree for cylindrical manupulator

[@asodemann3]

X2 is pointing away from you. Using your right hand, point your thumb away from you. Z1 is pointing up, so point all of your fingers up. Now, what direction do you have to rotate to get Z1 to point to the right, like Z2? You have to rotate 90 degrees to the right, the same direction that your fingers curl. That's why alpha is positive 90 degrees.

[@yashpamnani5391]

@@asodemann3 OK ma'am I got little confused with the axis of rotation i.e. axis around x2. But it is clear now Thank you

[@desi_in_us5548]

I think in the first problem X2 should rotate -90 about Z1!!Am i right??

[@asodemann3]

Keep in mind that we are ALWAYS rotating the frame n-1, not the frame n. So, when we are figuring out how much to rotate around Z1 to get the X axes to match, we need to think about how to rotate X1 around Z1, NOT how to rotate X2 around Z1.

[@athinthomas]

How to attach frames using DH method

[@asodemann3]

Look back to the Kinematic Diagrams unit of this playlist: kzbin.info/www/bejne/q6WXpo1sjt-pbNE

[@haroonjavaid3918]

Respected Madam you wrote alpha for row 2 is 90 degree..it is 180 degree.if i rotare z1 axes around x2 then alpha should be 180 degree..90 degree is point upward or simply in perpendicular direction...

[@asodemann3]

Haroon Javaid Which example are you referring to?

[@maker72460]

No! +90 is correct and she is right. Remember Y never plays a role. You have to rotate frame 1 about X2 so that Z1 and Z2 aligns. And Positive 90(ACW) makes that happen

[@haroonjavaid3918]

Respected Madam you alpha for row 2 is 90 degree..It is not 90 degree...It is 180 degree...

[@MrPrateek9711]

Haroon you need to rotate along Y1 with -90 to align Z1 and Z2, so -90 is correct

[@maker72460]

No! +90 is correct and she is right. Remember Y never plays a role. You have to rotate frame 1 about X2 so that Z1 and Z2 aligns. And Positive 90(ACW) makes that happen

[@qalababbas3690]

is r link length or joint offest.Cant understand. And what is d

[@asodemann3]

It might be that you missed the videos that come before this one in the series. One way to easily browse the videos in order is to visit my website, www.robogrok.com. The Denavit-Hartenburg stuff is in Robotics 2. Then, click on a topic and the videos are arranged in order.

[@haroonjavaid3918]

Angela Sodemann Please tell me

[@asodemann3]

Haroon Javaid The z1 axis is pointing up, but the z2 axis is pointing to the right. These two axes are 90 degrees apart. Rotating the 1 frame around x2 is the same as rotating around y1, since these two axes are in the same direction. So, imagine that we would rotate frame 1 around y1. The axis y1 would stay the same, only the z1 and x1 axes would move. How far would we have to rotate in order to get z1 to point to the right? We would have to rotate 90 degrees.

[@dradexx]

you would have to rotate by negative 90 degrees.

[@imvention5696]

In previous videos, u said compare theta zn-1 and zn..but this time u compare zn with zn+1..

[@asodemann3]

Can you give a timestamp?

[@imvention5696]

@@asodemann3 at 22:40, u compared axis 2 with axis 3 and not axis 2 with axis 1.. in previous video u said for theta, look at zn and zn-1..

[@asodemann3]

@@imvention5696 Robo Kit I am sorry, but I don't hear or see a reference to frame 3 around that time. We are using theta 2, which is a rotation around Z1, then we look at how X1 has to change to match X2. Since we are working on row 2 at this time, this is a comparison between n and n-1

[@imvention5696]

@@asodemann3 i just happened to get confused.. is it ok if i remember it like this, for theta, always compare to the frame at the front? btw ur videos helped me to complete my assignment. huge thanks miss angela

[@asodemann3]

@@imvention5696 Hmmm... I guess it depends on what you mean by 'at the front' . You should be camparing to the frame just before. So, if you are working on row 2, compare to frame 1. When you are working on row 3, compare to frame 2, and so on.

[@muhammedmacit7191]

sorry ı want to write clockwise

[@asodemann3]

Which of the examples in this video are you referring to? Can you give me a time stamp?

[@haroonjavaid3918]

Angela Sodemann please reply me

[@mrpossible5696]

8:42

[@amr.a-m8350]

Thank you for your explanaition, could you please give us the examlpes in a sheet of paper (word or pdf format)?