Matt Bauer double knee joint for SES

Lynxmotion Legged Robots
1

This topic came up in the “KHR walks” thread. I thought it was really worthy of a separate topic.

I got to looking at the Matt Bauer double knee joint and thinking about how it could be done with the SES. This is what came of that process.

This was one of those times when I just felt like tinkering with brackets in true erector set fashion. I built the leg and then did the 3D CAD model. Here is how the Matt Bauer dual knee joint might be fitted to a BRAT. These images show the left leg.

Standing:
http://www.thedynaplex.org/robotics/bipeds/BRAT/img/BRAT-leg-dual-knee-joint-left-standing.jpg

Crouching:
http://www.thedynaplex.org/robotics/bipeds/BRAT/img/BRAT-leg-dual-knee-joint-left-crouching.jpg

Full forward bend:
http://www.thedynaplex.org/robotics/bipeds/BRAT/img/BRAT-leg-dual-knee-joint-left-forward.jpg
I don’t think adding this knee joint, using the ASB-09 as shown, would add much, if any, height to a BRAT. It certainly adds some interesting possibilities for motion. :wink: This leg really needs a fifth joint between the knee and ankle to be fully usable though.

8-Dale

2

Are you using the Short “C” brackets for that model? If not, the leg is a bit long for a BRAT.

3

The ASB-09 is the short “C” bracket.

8-Dale

4

Hmm, Maybe its just the picture making it look long then.

So what kind of servos would you use for ti?

5

Wow nice design i might try that with my brat. The dual knee from what ive seen really improves the performance of bipeds alot. What bracket do you have between the two knee servos?

6

It would probably be outfitted with standard sized servos, strength would be absed on preference and application

7

To build a BRAT from scratch now, with or without the double knee, I would not use less than the HS-645MG all the way.

8-Dale

8

Umm…

I am not sure that the double knee as shown provides any benefit. The lower servo doesn’t seem to move at all.

And in some of your configurations, you have a C bracket cutting a servo in half!

9

I couldn’t figure out any benefit. and it makes the leg longer/heaver.

Alan KM6VV

10

Dale, you have become quite good with Alibre!

The design is redundant. All it would do is provide more “bow” to the knee joint area so that the leg is more of an arch instead of a sharp 90deg bend. What the brat really needs are hip joints or rotating ankle joints. To me, one might as well build a biped pete if they are looking for greater DOFs.

The brat is a special class of biped with its 3dof legs but certainly one could modify the legs but I sense trouble with out hip joints, which would be needed to shift its weight. The taller the bot, the less 3dof per leg will work.

11

Yes, both knee servos move. Why wouldn’t they? I just have not shown all the range of motion of both knee servos. That can be fixed easily though - I just have to add a new configuration to the model.

How do you figure this? Nothing is being cut in half anywhere.

8-Dale

12

Of course it makes the leg heavier, Alan, because there is an additional joint in the leg. This probably does add a small bit to the height of the robot, but it will not be that much.

I already specified that this double knee joint really needs to be in a 5DOF leg. There needs to be a joint between the lower knee joint and the ankle, just as shown in the link for the Matt Bauer joint.

As for benefitting the BRAT, the extra knee joint adds more flexibility in motion. It also provides for a better kick move.

8-Dale

13

Thanks, Mike. :smiley: I learn as I go and it is taking me less and less time to create models.

Each knee joint servo only has to move half as far as would be needed with a single jointed knee. As stated in the orginal text for the Matt Bauer knee, it means faster motion.

I guess I am just going to have to upgrade MsBRAT with the Matt Bauer knee joint and fiddle with it. I am having difficulty getting her walking using HSERVO.

Yes, the BRAT is special - no doubt about that. You may or may not be right about this, Mike. I think actual experimentation with the double knee joint is needed to actually test how it performs.

I’m going to model the right leg with the double knee. Then I can really do some checking as to ranges of motion and such. I definitely do not think the double knee is redundant. This is new for the SES, so we will have to see how it works.

8-Dale

14

A picture is worth a thousand words …

http://www.siennahanon.com/Robotics/linux_guy_double_1.jpg

http://www.siennahanon.com/Robotics/linux_guy_double_2.jpg

:hug
Caitlyn

15

Dale,

This one uses two ASB-10s and one ASB-15:

http://www.lastantique.com/robotics/double%20knee%20joint.jpg

16

I considered this, but it would not be built like the Matt Bauer dual knee. It’s just not the same joint.

8-Dale

17

Yes indeed. I still don’t get what you are saying though. You can’t see the full range of motion possible in a few pictures. I’ll export the model in all configurations to a 3D PDF. You can then see the model from any angle you want to look at it. :slight_smile: Maybe that will clarify things. I’ll add a couple more configurations to show different moves too.

I’ll accept hugs from you anytime. :slight_smile:
hug back

8-Dale

18

Well im gonna purchase the kit soon to expierament with. And heres some examples of what the dual knee joint can make a bot do:
youtube.com/watch?v=1vWU6FAwA3Y-robonova
Bauer from what ive heard, got the idea from the Jap. robo one bots.

19

I’ve seen that video, and it is what really got me interested in the double jointed knee. The BRAT would not get that full range of motion with just 4DOF though. It would require that fifth joint between the knee and ankle for full range motion.

8-Dale

20

Yeah the video got my attention also. Im going to buy the dual knee from Bauer independents soon and im going to compare it with designs like what linuxguy made and finally compare it to only a 1 servo knee. Im pretty sure the results could be the same with the dual knees but i wont know until i try.