Servo Control for perspective project
The Captain
Posts: 60
I have recently just finished an engineering course where we got to play with the BOE-BOT for the class project. It was really fun, and easy to program because I had already and experience with TI-BASIC.
The robot I want to do is a build a spider. What I am wonder is how would i go about controlling the 58 servo's required to leg movement? 2 B.O.E. in asych to split the work or what?
Halopema Spider
The 8 long legs requies 6 servos to function.
The 2 short legs beside the fangs require 5 each.
I DO NOT CURRENTLY OWN a Stamp, B.O.E, OR the 58 servo's. I have to save up the money for this project. The high torque servos are rather $$, and that's not even including the hardware for the exoskeleton.
It will contain the following once completed:
Color Sensor(s)
PING sensor(s)
Camera(s)
2 6-Axis robitic arms
GPS
FlexiForce Sensor
RF or Bluetooth
Compass
PIR Sensor
TSL230 Sensor(s)
Piezo Vibra Tab(s)
Sensirion SHT1x
EMIC TTS
LED's
I will post a 3D model fron AutoDesk Inventor once I have completed my sketches and begin modeling it.
The robot I want to do is a build a spider. What I am wonder is how would i go about controlling the 58 servo's required to leg movement? 2 B.O.E. in asych to split the work or what?
Halopema Spider
The 8 long legs requies 6 servos to function.
The 2 short legs beside the fangs require 5 each.
I DO NOT CURRENTLY OWN a Stamp, B.O.E, OR the 58 servo's. I have to save up the money for this project. The high torque servos are rather $$, and that's not even including the hardware for the exoskeleton.
It will contain the following once completed:
Color Sensor(s)
PING sensor(s)
Camera(s)
2 6-Axis robitic arms
GPS
FlexiForce Sensor
RF or Bluetooth
Compass
PIR Sensor
TSL230 Sensor(s)
Piezo Vibra Tab(s)
Sensirion SHT1x
EMIC TTS
LED's
I will post a 3D model fron AutoDesk Inventor once I have completed my sketches and begin modeling it.
Comments
You've got a lot of sensors and other actuators on your list as well. You're clearly going to need a bunch of processing power just to service all the bits let alone any "making sense of the data". You might consider using the Propeller instead of a Stamp. Normally I'd suggest using the Propeller for everything, but you have so many devices planned that there's just not enough I/O pins available. You could devote a Propeller for each group of 28 servos, but that's overkill in terms of processing power. You could build your own I/O extender for use with the servos or you could just use the Serial Servo Controllers since they'd do the job well, are already developed, and are similar in cost to a Propeller/Board package (about $80 for 28-32 servos). You still might need two Propellers because of the number of sensors, but you might consider learning the SX-48 and using Parallax's SX-48 Prototype Board. They're only $10 and have 40 I/O pins available. You could develop your own version of the Servo Controller and develop a sensor board to monitor most of the sensors and provide reports to a "main" processor like the Propeller. The SX-48 really isn't suitable for something as complex as your spider controller, but it could sure off-load a lot of
the simple I/O processing with the number of pins available.
THe wulfden propeller board can easially be modifyed so you can daisy chain additional boards to increase your servo capability.
One thing you might need to consider is the power requirements of that many servos. 6 DOF is a lot of motion, and can alternatly be "simulated" with 4 servos, thus reducing your servo, hardware and power requirements. Just a point to think about is you don't need to 'mimick' all the motions of an appendage for it to work correctly.
For an example, look at the HEX and QUAD crawlers. Each leg has 3 servos, and it's mobility is very good. By adding a rotator servo at the sholder (first servo), you can mimic 99% of the movment of a true leg, with only 4 servos.
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Just some humble views on this other wise awesome project... Good luck!!
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Propeller + Hardware - extra bits for the bit bucket =· 1 Coffeeless KaosKidd
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If you need high torque servos and are on a budget, I would suggest looking at Blue Bird servos (www.slickzero.com), or even contacting their distribution center if you plan on spending so much on servos. Blue Bird servos are just as powerful as hitec's high torque servos but perhaps not as "finished" or "refined." You may want to try some out first hand before you decide to get 50 of these.
I made a road map for the project. it's a very long one spand an estimated 7 years, but probably going to take 10.
I also think it would be cool to have it walk around the yard during Halloween, that will scare the Smile out of the kids.
Goals for my Spider Robot
1 – 6 months from now:
1. Prototype leg assembled and working
6 months – 1 year from now:
1. 1 fully functioning leg
2. Basic layout of design
1 – 2 years from now:
1. 4 fully functional legs
2. Walking algorithm in place
2 – 3 years from now:
1. 10 fully functional legs
2. Complete chassis of robot and cosmetics
2. Complete walking algorithm
3. Speed control
3 – 4 years from now:
1. Radio Control
2. Ping Sensor integration
3. Ability to climb stairs
4 – 5 years from now:
1. Video
2. GPS
3. Data logging
4. Motion Sensing
5. Environment Sensing
- Wind
- Temp
- Humidity
- Tilt
- Collision detection
5 – 6 years from now:
1. Live Data feed to PC
2. Lay “babies”
- Control
- Direct movement
3. Autonomous
4. Mapping
- Build a “map” of its world to know where it can and can’t go
5. Sense when it’s time to “eat”, recharge
6 – 7 years from now:
1. Ability to pick up objects with 2 arms
I may have forgot some things, or some things maybe be added.
Estimated cost once fully completed: ~$20K
Eidt:
Embedded PC's will be much later down the road. I have just begun my Computer Science Degree, so I'm trying to get that done. Plsu I want to learn as many languages as I can, I will always be programming(keeps the mind sharp, and alert) .
Edit Again:
If anyone has SolidWorks 2006, can you please go here and download and convert the files to STEP files so i can use them in Inventor. Your help would be much appreciated.
Edit Again:
I was able to get the files converted.
Post Edited (The Captain) : 8/30/2006 8:40:39 PM GMT
PS:
The spand of the robot is looking to be about 10ft across.
... and DON'T forget the remote emergency stop! I don't wanna' turn on the news and see "Giant robot goes on rampage thru city, finally stopped by millitary A-10 attack plane..."
Maybe a R/C glow plug engine w/ alternator anyone???
Some of the larger four cycle "hobby engines" may do the trick. Salvaging something like a leaf blower or chain saw engine may be more appropriate.
As far as the "alternator", use a DC motor as a generator, and you should be good to go.
For starting out, I'd think about sticking with "wall power" and just have the cord dragged around. Use a white cord, and call it a thread of "silk". You could use some weight to simulate the presense of the generator. Then when you have things worked out on walking, etc., worry about the generator at that time.
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John R.
8 + 8 = 10
Use a leaf-blower or chainsaw engine. not only are they cheaper, but they're a biit more rugged, too.
(And you probably won't have any problem with the extra weight.. )
There's a bit of a problem with the power generation, though...
Even at 1000W, it equates to almost 80A/12V, which is 'a bit of power'. you need a rather hefty alternator to get that kind of juice, and if you want a bit of leeway, say up to 1500W, we're suddenly talking about 120A.
I suggest you invest in the largest car-battery you can get hold of and run it with a heavy umbilical at first.
(If you're working in a garage, you could just clip a couple of leads onto the battery in the nearest car... )
What kind of controllers will you be using?
(I assume the actuators are steppers)
In a project this size it may be a good idea to consider the placement and cooling of them already during the early phases of construction.
You may also want to place (some of) the motors/actuators in the body and use steel wire 'tendons' to transfer the power to the joints.
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However, this is for the big Spider. I can actually use servo's for the minature spiders i plan on making. The will have a span of about 3' if fully laid out. These will be light because the frame doesn't need to be as thick to support the weight, and forces acted uponit.
Actually, most chainsaw engines are not designed for continuious use, either. I would look for a lawnmower or a big leaf blower (such as the backpack kind). Used lawnmowers can usually be had for a song, and some have electric start...
>> You may also want to place (some of) the motors/actuators in the body and use steel wire 'tendons' to transfer the power to the joints.
Very good idea. Also, longer actuation lengths are available. Check out http://www.surpluscenter.com/ if you haven't already; they often have this kind of stuff for cheap - both electrical linear actuators and hydraulic cylenders & pumps.
Finding a motor with an intact electric starter...
Add a couple of decent batteries and stick in some power-management software, and it'll start the gas engine only when needed.
(The neighbours will like that... As soon as they get over the idea of a huge robot walking about... )
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Don't visit my new website...
Heres the pic of the actuated arm Im designing. In actuators go as follows farthest to closets.
200lbs of force - 4in stroke
165lbs of force - 3in stroke
165lbs of force - 3in stroke
200lbs of force - 4in stroke
165lbs of force - 2in stroke
It's reach is 48" long, and 20" high
Estimated mass of arm in picture ~12kg
Almost 100Kg just in the arms...
Crikey!
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Don't visit my new website...