MSR-H01 Mandible / Gripper Kit

Hexapod Robots

MSR-H01 Mandible / Gripper Kit

Postby Matt Denton » Thu Apr 23, 2009 4:35 pm

Well this is clearly inspired by Zenta's beautiful A-Pod, and having seen the 3DOF gripper head in action I decided to see if it was viable to make a gripper head for the MSR-H01 hexapod. I have approached this with budget in mind, so the kit will not be able to lift the kind of weight Zenta has achieved with A-Pod, but I have tested it with approximately 125 grams which it seems pretty happy with, including walking while carrying the payload.

Image

Adding an abdomen would help to shift the COG back to the middle with heavier payloads, but in order to keep the cost of such a kit down I hope to use low cost servos, in whihc case 125 grams will probably be the limit.

Image

The current servo list is as follows:

Pan: HS-225BB
Tilt: HS-475HB
Twist: HS-225BB
Grip: HS-322HB

I used these servos so that people who already have a pan/tilt kit will be able to use their existing pan/tilt servos. Only one servo is needed for the gripper as the second mandible is gear driven from the first, thus keeping cost & weight down.

Image

As far as a sensor for the gripper is concerned I have a couple of thoughts on this:

A) With the current design, the HS-322HB is a pretty low torque servo, but with a reasonably good gear box, so although driving the gripper fully closed on to an object causes the servo to stall, it does not draw much current and doesn't get too hot. If I used a high power servo for this then it would most likely burn out.

B) I have considered making a small in-line current monitor or pressure sensor unit to reduce drive to the servo.. but again up goes the price.

C) I have just made a second design of gripper whihc uses a spring return mechanism to close the grippers, in this case teh servo can only drive the grippers open, but is disconnected in the closing direction where by the spring takes over. This is a pretty good solution, as no sensors are need to safely grip an item, and the servo takes no current when the grippers are closed! The spring used is pretty critical, as the servo has to be able to back drive the spring in order to open the gripper, but If the spring tension is nearly matched to teh force the servo can apply, then the closed force of the gripper should be close to that of the servo if it was directly connected.

Image

With the addition of the modified pan/tilt/twist mechanism, the gripper sticks out a little further than I would have liked, but without making expensive specialized brackets, or modifying the hexapod top plate, this is about as good as I can get it.

Image

To complement the Gripper head I have also implemented head auto levelling within the HexEngine firmware, this will be available in the next V1.2 release. I will see if I can shoot some video soon.

I have no idea how much the kit will cost yet, as I am still trying to simplify the design. In order to keep the weight & cost of the gripper head down, the kit will be made in acrylic.
Matt Denton
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Re: MSR-H01 Mandible / Gripper Kit

Postby pem » Thu Apr 23, 2009 5:18 pm

A very fine addition to the MSR-H01 kit. What level of support in the PIP command set do you plan to include?
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Re: MSR-H01 Mandible / Gripper Kit

Postby Matt Denton » Thu Apr 23, 2009 6:57 pm

I have added a few CONFIG commands for head twist and grip servo limits:

TWM: Twist Middle
TW+: Twist Max
TW- Twist Min
MAM: Mandible Middle
MA+: Mandible Max
MA-: Mandible Min
AHL: Auto Head Level

The 'H' PIP command will take two additional parameters for Head twist and grip.
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Re: MSR-H01 Mandible / Gripper Kit

Postby jebidiam » Thu Apr 23, 2009 7:12 pm

This totally rocks!! I will definitely get one of these for my MSR-H01.
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Re: MSR-H01 Mandible / Gripper Kit

Postby Zenta » Thu Apr 23, 2009 9:42 pm

Great work with the head Matt! :D Now you've made a B-Pod ... ;) "A beetle inspired hexapod". You could also add some rubber to the inside of the mandibles to make the grip even better. I liked your spring solution, I've also played with that thought but didn't find a way to make the sping less visible. You sure save some weight by using only one servo for the mandibles (I wish I had a CNC machine... :roll: ).

Anyway I'm looking forward to see it in action!

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Re: MSR-H01 Mandible / Gripper Kit

Postby Noodle » Fri Apr 24, 2009 10:46 am

Awesome. Great to see that you're expanding on your platforms.
Making robots from a school students wage :(
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Re: MSR-H01 Mandible / Gripper Kit

Postby plingboot » Fri Apr 24, 2009 10:47 am

i like that matt - really great take on the zenta ant head - add me to the list of buyers. ;)

any thoughts on adding a vertical plate which could hold either/both an SRF ultrasonic module and a wireless cmos camera (ie the one used for blob tracking) - so it could be a full-on mulit-purpose head?

will you be able to add some kind of mandible 'nipping' to PS2 control?
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Re: MSR-H01 Mandible / Gripper Kit

Postby Matt Denton » Fri Apr 24, 2009 11:08 am

Zenta wrote:You could also add some rubber to the inside of the mandibles to make the grip even better.


I have some standing by :) just need to stick it on.. but I'm not sure if it will stick well to the curved surface!

plingboot wrote:any thoughts on adding a vertical plate which could hold either/both an SRF ultrasonic module and a wireless cmos camera (ie the one used for blob tracking) - so it could be a full-on mulit-purpose head?


Yes, I have a plan for this, however, although practical it doesn't look too good, so giving it some more thought.

plingboot wrote:will you be able to add some kind of mandible 'nipping' to PS2 control?


Yes I guess I will be able to add a twist and NIP option... ;)
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Re: MSR-H01 Mandible / Gripper Kit

Postby beez » Sat Apr 25, 2009 5:39 am

Oh, this is so AWESOME!
Put me on the list, I'll take mine in Black please! :)

In case you are still taking suggestions, I was going to do something just like this, and use the pan/tilt to start.
Can you re-use the pan/tilt brackets? My bet is most folks already have those and it would help control cost.

Peace!
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Re: MSR-H01 Mandible / Gripper Kit

Postby Matt Denton » Sat Apr 25, 2009 8:43 am

beez wrote:In case you are still taking suggestions, I was going to do something just like this, and use the pan/tilt to start.
Can you re-use the pan/tilt brackets? My bet is most folks already have those and it would help control cost.


Unfortunately the pan/tilt brackets will not be able to be re-used, this is due to the fact for the additional weight I have added a tilt bearing on the opposite side of the servo horn, so a very different design. I will probably only make the heads in black acrylic. :)
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