Let's Make Robots!

GRAB-E

Wanders around and grabs your stuff

Update 2011-10-06: Melty, melty

Poor GRAB-E. His foolish creator left him in the garage for a few days after taking him home from a trip. The hot summer sun melted his polymorph sonar bracket and parts of this tracks.

Last night I got around to carefully picking off the slagged polymorph. I remounted the sonar with hot glue for now. New tracks just arrived this afternoon, so hopefully I can fit him up today.

I also tried out some new NiZn batteries in GRAB-E. They are AA sized and have a nominal voltage of 1.6V. Fully charged, they are about 1.8V. Since I used a LDO voltage regulator and a 4xAA battery pack, these work out great. Now GRAB-E starts off at 7.2V instead of 6V, and runs for a lot longer. Also, since the motors run directly from the batteries, he should really kick it into high gear now!

While testing out the new batteries with the old melted tracks removed, I noticed a distinct wobble in one of the drive sprockets. I tried to unbend it, but I probably just made it worse. Ideally, I should take him all apart and try to bang the shaft straight again. Realistically, I might not see much of an improvement for all that work. I'll try the new tracks and see if he runs OK.

Update 2011-07-13: Integrated IR circuit and updated code

I moved the interface circuitry from a breadboard to one of those little circular protoboards from Radio Shack. It's only about 5/8th of an inch (or 1.5cm) in diameter. Getting everything on was a tight fit, but now it is hot glued to the little wooden block behind his sonar. 

As usual, check GRAB-E's build blog for more detail. I'll add new pictures and video soon.

Update 2010-09-30: New Head

I replaced GRAB-E's head and reduced my servo count by one by combining his sonar sweep with his claw. Check GRAB-E's  build blog for more detail.

Update 2010-09-12: The CLAW!!!!

GRAB-E finally gets some equipment to match his moniker.

Update 2010-02-04: Uploaded new primary image.

Still building, but here is GRAB-E. So-named because of the WALL-E style track configuration and the fact that I will build my first gripper for this bot.

You can also view the build blog for this bot.

I added a video showing GRAB-E's manueverability.

GRAB-E was originally somewhat of a distraction from my more complex plans for the Mr. Basic Challenge 2, which never really got finished (but will, someday!). I was up at 4 AM and I needed to do something fun that didn't involve load fabrication noises from the basement. 

CHASSIS

Based on a Tamiya Remote Control Robot Construction Set. I sacraficed my earlier (incredibly lame) robot for this one. I've reconfigured the tracks from the original to a triangular set up with the drive sprocket at the top and two idlers below. You can see the track setup in the main picture.

Dragging behind an Arexx roller wheel purchased from DAGU. This rear wheel works great, but definitely limits GRAB-E to an indoor, smooth floor environment. I'd be interested to hear ideas on a different approach that would let me take better advantage of the tracks and open this bot up for a greater variety of terrain.

The advantage of this set up is manuverability. The shorter track length makes turning easier.

 

BRAINS

Originally I sacraficed the brains from my Start Here Robot. Those brains eventually when to Robot Leader, and I have nowI built a new set of brains based on the Picaxe-40x2 loaded on the Picaxe-40/28 protoboard. Stacked beneath the protoboard is a DAGU Mr Basic motor controller board. The open space on that board has power regulation, a power switch, servo interfaces, etc.

SENSORS

I added an SRF05 sweeping ultrasonic range finder using a home-made pan-tilt based on the DAGU sensor brackets.

GRABBER

I finally built the grabber from which the bot gets his name. It is based on a single servo, with a plastic gear mounted where the servo horn should be. The gear is coupled with an orange piece of plastic that is actually a throw-away bit from a Canon ink cartridge. the driven gear is meshed with an identical one (also mounted to an orange claw bit). The second gear/claw is held on with a simple metal frame I banged together and hot glued to the servo. I hope to improve this setup later.

The whole mess is in turn hot glued to another DAGU sensor mount forming GRAB-E's wrist. I modified a DAGU sensor mount to work as the up/down control for the grabber arm. Check the build blog for more info on the sensor mount mod.

Later I may add pressure and position sensors so GRAB-E can be more precise. For now, I'm happy I have a decent mechanical design that lets him grab stuff.

More coming soon!

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Have you thought about adding my servo force sensor to tell if your servo isn't moving (The gripper is closed onto something) http://letsmakerobots.com/node/27892

I have indeed thought about some sort of feedback on the grabber. I may use a method similar to the one you describe, or use some conductive foam to make a tensile sensor.

Hi Ignoble,

What is the servo on the front of GRAB-E in the video you posted. I have noticed that a number of people on this site add a swivel point to a servo opposite the horn to provide strength and prevent the torquing that might result from only attaching to one side of a wider leg or other object. I was wondering if servos come with either a swivel point built in opposite the axis or with the axis extending from both sides of the motor. You seem to be using such a servo in GRAB-E.

Thanks.

It is actually just a normal servo. I fabricated a simple bracket by bending some sheet metal around the body of the servo. The bracket runs along the top, back and front, with some overhang on each end in front of the servo. It is crudely hot glued in place.

I have heard of people who will open up their servo, and drill out a hole in the case opposite the axis of the servo horn. Then they use this to mount a shaft of some kind to support that back side of the servo.  

Im currently building my first robot and im using a tamiya dual gearbox with the tracks as well. When mine arrived, one of the pinion gears was all mushed and I have the same problem as you with a gear that has a real wobble with it. When testing the gearbox and motors it would make a horrible noise. I have managed to silence it a bit with lube. The other side appears to be perfect (no wobbly gears) and doesnt make any horrible noise.

The Tamiya gear set it notoriously noisey. I don't think my set wobbled when it was new, and if you received a mangled pinion gear as well, you should contact the seller for a replacement.

The set should come with lubrication, and the instruction manual indicates that you should lubricate the gears during assembly.

Still, they are noisy little F'ers, aren't they?

Except I am going to put mine on a Rover 5 base.  It stinks that some of GRAB-E melted.  It must of got really hot in your garage.

Got him all fixed up. Pretty much.

His grabber programming still sucks, though. ; j

You must enter this robot in the Search And Rescue challenge

http://letsmakerobots.com/node/27789

I plan to. His programming right now is such complete crap as far as his claw is concerned. The challenge is just what I need to program him for a focused task.