Mobile Robot Arm
@ November 27, 2008
- Actuators / output devices: 8 HS-475HB servos, 2 GM2 224:1 Offset Motors
- Control method: BlueSMiRF Gold
- CPU: atMega8
- Power source: 8 1.2v Ni-MH 2500Mah (9.6v)
- Programming language: C
- Sensors / input devices: 2.4GHz Webcam (eventually)
- Target environment: indoor
I made this CAD in Google Skechup after I had an epiphany. I thought this would be a really cool idea, and would give me some good experience.
Here is how it will go:
It will use 1/8inch Sintra, simialer to PVC
The Servo brackets will either be custom made from bigbluesaw.com or pre-made from Lynxmotion.com
The gripper itself will also, either be homemade from aluminum or bought.
On the gripper, the actuator of the gripper itself will either be a regular DC motor with a Motor Controller or a Micro Servo (HS-81) Most likely the latter.
I will be using my custom Atmega8 MCU Board, which has fourteen servo connection ports.
Taken with my webcam so please excuse the crapiness
And I made an AVR Programmer from a kit from adafruit
I am aiming to use all eight servos as hs-475hb servos because they are cheap and sturdy (~$15).
It will be controlled via Bluetooth from the UART connection on the Atmega board to a nearby laptop with a Bluetooth USB Dongle.
Eventually I will find a suitable wireless webcam, and skin the plastic off and mount it on the bot.
Does anyone have any reccomendations as to the accessories of this robot? (motors, servos...)
@ Sat, 2008-11-29 03:39
Sweet
@ Fri, 2008-11-28 04:42
Dual servos
@ Fri, 2008-11-28 14:45
I thought that would have
@ Fri, 2008-11-28 15:36
Since they are mounted
Since they are mounted back-to-back, they obviously have to turn in opposite directions, so that is the first thing to remember.
Second, put the two servos on the same output from the controller and not to separate outputs. If you use separate outputs, one will get it's "move command" before the other and start ahead of the other.
@ Sun, 2008-11-30 11:04
Yeah, I suspect the
Yeah, I suspect the aesthetics of having the two base servos mirrored might not be worth the added complexity of reversing one of the servos. Lynxmotion skipped that and just mounted both servos in the same direction. It does look a little odd and asymmetrical, but it's nice to just be able to use a simple Y-splitter cable to control both servos.
Don't forget that using two servos at every joint also adds more dead weight that the lower servos have to lift, which will reduce the amount of payload you can pick up. Again, I guess you have to decide how much you're willing to sacrifice for aesthetics. There's no right answer, just different priorities.
But really, my limitation with the Lynx L6 was the gripper servo -- it just couldn't squeeze very hard at all without stripping gears. I upgraded it to metal gears, and now they don't strip when I try to squeeze hard, but instead the servo just tries to draw so much current that apparently my 2.5 amp power supply can't feed it enough, so the servo jitters, and drops whatever it's carrying.
I would also definitely suggest that you go with a flat gripper like you've drawn, rather than the round 'fingers' that my Lynx L6 came with. It's pretty hard to pick things up reliably with the round one, and there's no good way to mount a pressure sensor to let you control how hard you squeeze things.
Dan
@ Sun, 2008-11-30 14:59
I was planning on doing
@ Mon, 2008-12-01 12:33
Hall effect sensor
Your plan probably wont work. depending on the size and strength of your magnet you may not get a reading with the grippers open beyond a certain point.
When you grip something, unless the object is ferrous then it won't affect the reading.
Ferrous metal used in the gripper construction may have an effect on reading.
I'd stick with force sensing resistors as previously suggested.
@ Fri, 2008-11-28 16:19
I cant believe I didnt think
@ Sat, 2008-11-29 07:02
opposite directions?
Might need a servo reverser on one of a pair so that they both move the same direction though, as jka points out, they are back to back.
Might be possible to modify one to turn opposite of the input signal, by reversing a few connections internally.
@ Sat, 2008-11-29 12:35
You are right. Silly me.
You are right. Silly me. Putting them on the same output will of course make them turn the same way and then it won't work.
Theoretically, if you opened up one of the servos and swapped the wires for the motor, to make it turn the other way and swapped the outer wires of the potmeter, it might work. Provided, of course, that the motor isn't soldered directly to the PCB in the servo.