Looking for lifter/grabber combination ideas?

[TasV]

Is it possible to construct a lifter arm with a grabber on the end that uses only one motor to lift it and operate the grabber at the same time? I've been messing with differentials in such setups but have been unable to get one to work.

[07jkearney]

Laurens Valk has made a robot that grabs and lifts using only one motor, perhaps you could use it for inspiration?

[TasV]

Yes... I've got his book and was thinking about this... The robot that came 2nd at the Australian Robocup National Finals used this design. I've been trying to incorporate a grabber into a forklift design. I can do it with two motors. I was just wondering if it could be done with just one?

Edited September 28, 2013 by TasV

[Ramacco]

It is possible and I did this. I made BI instructions for my robot, but they didn't turn out great. If you want me to, I can send you the file.

http://www.eurobricks.com/forum/index.php?showtopic=74118

[Alasdair Ryan]

I made BI instructions for my robot, but they didn't turn out great. If you want me to, I can send you the file.

http://www.eurobrick...showtopic=74118

Are those the ones me and freakwave did?

Edited September 28, 2013 by Alasdair Ryan

[Ramacco]

Alasdair: I was referring to the first you've send me.I just looked on my PC and found the newer files!! (sorry, long time not been able to use my LEGO, I have forgotten a lot about what I have and not ) Thank you for those!!

So I can send you the good Building Instructions, thanks to Alasdair and Freakwave.

[Alasdair Ryan]

No problem....

[CP5670]

The old 8094 control center set had a model like this. It worked very nicely and had both functions on the same geartrain. Since more force was needed to lift the arm than to close the claw, the claw would always close first and the arm was then lifted.

Edited September 28, 2013 by CP5670

[TasV]

Hi Ramacco. I was sifting through the 100's of emails on my work account the other day and actually found an email from you that I had missed. I was going contact you this week because I'm on 2 weeks holidays to thank you for your email. I get 30-50 new emails through my education email account every day so I apologise that I missed your email; sometimes I just don't see an email. It's a lousy system! If you PM me through the Eurobricks forum I will get it because I get the notification to my home email address. My robotics boys went on to compete in the state Robocup finals and we came 1st, 3rd, 4th, and 5th (my Son came 3rd) and then one of my boys went to the national finals and competed in senior rescue and came 8th in Australia and then also competed up in premier rescue and came 15th in Australia. So I'm very proud of them and am looking forward to next year.. which is why I am starting to put ideas together now so I can share it with them for their builds next year.

8094 looks interesting! I've been looking at 8062 to see the lift/grabber in that too. We've made a linear actuator lifter and a simple claw grabber (using a worm gear between the two jaws), but it is very large and ungainly. It works but I'd like a more compact robot. I also need to leave room for ultrasonic sensors to locate the can it has to lift and then it has to find a platform and place the can down on the platform without dropping it.

[TasV]

Ok... I've made a few little mechanical models of grabbers with differentials and can get it to work... but I am still stumped by a few things.

The first is related to your 2nd video, Ramacco, that shows the mechanism in manual mode, without the motor. The grabber starts open and then closes before the lift starts because the load on the grabber is less than that on the lift. Once the grabber is closed the load on the grabber reaches 100% and the rotation is transferred to the lift. The lifter lifts the grabber off the ground and here is where I am confused. You wind the mechanism backwards and I would have thought opening the grabber would have less load than dropping the lifter but the lifter drops first and then the grabber opens. Is the load going down, on the lifter, different to the load going up on the lifter (due to gravity I assume)?

I'm also confused about how you simultaneously supply rotation to the lift and the grabber whilst the whole mechanism is changing height without changing the height of the motor.

And lastly, your action is slightly different to what I have to achieve, however; I hope it will still work anyway. In Premier Rescue you have to lift the can up (that's fine) and then locate a platform and then drop it down. Yours picks the can up from one level and then drop it back down in a different place at the same level. I'm hoping that when the can is placed down on the platform that this makes the load on the lift exceed the load on the grabber which then causes the grabber to open. I think it will...

I would love to look at your instructions to confirm the ideas we have and to help clear up the confusion.

Thanks,

Simon

[Ramacco]

And lastly, your action is slightly different to what I have to achieve, however; I hope it will still work anyway. In Premier Rescue you have to lift the can up (that's fine) and then locate a platform and then drop it down. Yours picks the can up from one level and then drop it back down in a different place at the same level. I'm hoping that when the can is placed down on the platform that this makes the load on the lift exceed the load on the grabber which then causes the grabber to open. I think it will...

Yes, the intention of this mechanism was to put a can on top of a shelf. The arm will open when the you place the can back on a higher platform than were you have picked it up from. I have tested this myself and it works without a problem.

[Lost_In_Noise]

The 8479 Barcode Truck uses a similar function with flex axles. When the first axle bottoms out, the entire arm is lifted.

[Philo]

EV3 GRIP3R robot also has a single motor grabber/lifter. BIs here: http://www.us.lego.com/en-us/mindstorms/community/bi/

[TasV]

Thank you for the plans, Ramacco. That method of delivering rotation to the lift/grab differential is quite ingenious!

[TasV]

We finished the grab/lift mechanism. I apologise for the crappy video... Ipad videos are hopeless. It uses just one medium PF motor at the moment. When the new medium EV3 motor arrives it will take its place. The robot is not finished yet and is not programmed to do anything except loop through grab, lift, lower, and open, just to test the mechanism. It doesn't lift all the way to the top at the moment either.

Ramacco, we decided not to use the worm gear setup as it slows the whole thing down dramatically (with the large NXT servo motor... with the M PF motor it speeds up dramatically) and have attached the motor the same way you did (I think) in your first model. Thanks again for your assistance. Your plans were excellent.

The power is just on 60% at the moment. We'll probably drop it back to about 40%. It's very quick and uncontrollable at 100% power. Eventually it will have a touch sensor at the top of the lift to stop the lift. Other robot specs are: 4WD skid steer, touch sensors x2 at the front to detect collisions, two omniwheels at the rear (lift is at the rear of the robot) to support the lift. It will have ultrasonics attached to the back and another brick mounted eventually as well. The colour sensor under the lifter is to verify the can it has to lift up and red platform it has to place the can on.

Edited October 6, 2013 by TasV

[pspeth]

Tasv,

I would love any info that would help me understand the lift mechanism.

Thanks