Bipedal bot (TONS of questions)

[zemata]

Total mindstorms noob here. Would love to learn more about programing and robotics in general. Only successful creation of mine so far is a contraption that plays Pokemon Emerald on a GBA SP lol. My current supplies include one NXT 2.0 set and a large collection of Lego and Technic.

So here's the deal. I want to make a humanoid, bipedal robot that can....
-Walk forwards, backwards, and turn
-right itself if toppled (using arms and waist swivel. Maybe leg movement too)
-avoids walls
-recognizes humans (MAYBE could I use a RFID sensor for this? If yes, could I combine the previous feature into this sensor?)
-Speaks and reacts with speech to different circumstances
-Light up eyes that blink (already have this part done using the PF LEDs on port A of my NXT. Programmed them to shut off for about 0.1 seconds intermittenly)
-maybe more.....

Parts I'd like to use externally (Not inside the robot, but connected via a grouped up "umbilical cable")...
1 NXT
1 4AA Battery holder

Parts I'd like to use internally...
5-6 Mindsensors microservos
1 set of PF lights
1 sensor to detect if robot is not upright (Don't know if I need a gyro, acceleration, or compass for this)
1 RFID Sensor OR 1 RFID sensor and Ultrasonic sensor
1 8 channel servo controller for NXT (mindsensors)

excuse the crude drawing

Now for the questions...
-Does the mindsensors servo controller allow for individual movement and measurement of each micro servo attatched to it? or can you only monitor measurements from 1 servo using 1 dedicated slot on the NXT?
-Can anyone with mindsensors servos or micro servos compare the torque for me in an easy to comprehend way to other Lego motors? Like this website http://www.philohome.com/motors/motorcomp.htm just with the mindsensors servos added. I'd like to use the smallest motors possible while still being able to measure their movement and bear a decent load. I'd like to know ASAP so I can order these parts.
-Do I want a gyro, acceleration, or compass sensor to determine if my robot is not upright? (bearing in mind that wobble will occur as it walks) http://www.teamhassenplug.org/NXT/NXTSensors.html
-Does anyone know anywhere I can get text to speech software to make samples for my bot? Should I be looking into voice synthesis? I know how to edit audio using programs like audacity and I also know how to convert them into proper format for the NXT.

Tired....may have more questions later. Thanks for your time!

[timpattinson]

-Do I want a gyro, acceleration, or compass sensor to determine if my robot is not upright? (bearing in mind that wobble will occur as it walks) http://www.teamhassenplug.org/NXT/NXTSensors.html

Acclerometer, i think.
I know the HiTechnic one has a tilt sensor in it.

[doc222]

Getting it to stand after a fall will be hardest part by far. The legs in alfa rex wont bend enough. The hips as well as ankles would need to be in the loop(able to bend at each point) as well i think. So any "shuffel" stepping would be ok to walk, turn. but to right its self will need alot DOF and power. Think about it like this; Lie on floor with legs stiff and try to stand up? How hard is that? Even asimo when it falls" cant get up" lol. Now I have seen a quad do this fully autonomous, see "Big Dog" on you tube from Boston Dynamics as well as other toy bots that are purpous built.

R/c Servos come in a few types and for big power they get rather expensive as well. hard to use a gear train with them as well, they suite best in a bell crank configuration. I am not sure but the ones that have full rotation wont count degrees( I may be wrong here someone who uses these may shed more light on this)

Best bet if new to Bipeds and Lego, keep it simple to start as these projects can get very very complcated very fast in Bipeds or we would see alot more Bipeds of Lego doing many things.

In my projects of many years in bipeds, I have still to get any arms on it do to many factors, weight, expense and will need a better design that what I am working with now. One thing I found through testing is that for the arms to be of any use will need to be almost as power full as the legs. with that conclusion and testing a working model i ended up with a quad known as X4 "sloth" ended up with for arms and four hands it can climb ladder and even a over hang but it is SOOOOO slow that most people can not watch it take almost 10 minutes to climb 3 feet up and under the roof a few feet. only a mom sloth could love it lol.

Best of luck and as you go take photos and videos it will help you see things in it that you may miss in real time.

Regards

Doc "Bipedial dreamers club"

[zemata]

Thanks for the replies! Good to see that this forum is active.

About the legs. I'm not using a direct copy of alpha rex's legs, but a slimmed down version using the microservos from mindsensors. I may put another degree of freedom at the hip of each leg (forward and back).

The biggest things I need to know before I get started are my questions on the mindsensors servos.
-I need to know how powerful the microservos are
-do they measure degrees, rotations, or both?
-If I power about 6 of them through mindsensors 8channel servo controller, can they be controlled independently of eachother, or only all run at once? Can they return individual degrees and/or rotation data when using the 8channel controller?

As soon as I know these things I can place an order and get started.

[timpattinson]

-If I power about 6 of them through mindsensors 8channel servo controller, can they be controlled independently of eachother, or only all run at once? Can they return individual degrees and/or rotation data when using the 8channel controller?

This vid uses the MS servo controller, and 5 servos You can see that they can be controlled independently

[dimasterooo]

Can they return individual degrees and/or rotation data when using the 8channel controller?

I'm not sure but I think so. The I2C addresses are specified in the user guide (http://www.mindsensors.com/index.php?mo ... ile_id=710). If you really wanna know for sure, you can contact them; their customer service is great and really fast (my experience).

[zemata]

alright cool. I just emailed asking whether their servos sense position and if they can send that data through the NXTServo-v2 to the NXT.

Now I have a new problem. I'm reading that these servos can't rotate 360 degrees. They don't have continuous motion and don;t have unlimited rotation correct? Why wouldn't they? I need the smallest, Lego-mountable servos that can send position data and rotate unlimited in both directions that I can find. Does such a thing exist?

[doc222]

Couple things to point out "Micro" servos in the Rc world have very little power. When an R/c thing needs big rc sevo power they use much MUCH bigger servos even up to 1/4 scale. In my research a long time ago about this very thought. should i use the 8 channel servo or the Mmux. It came down to a few points. If I remember correctly here( iM getting old and at times forget) but to have servo(rc) equal to legos gear reduction servos, micro is not even close. But the heavy duty ones do(not from mindstorms but from Rc suppliers) these things are not cheep and heavy as well, one could buy a few lego ones for the cost (about 100+$ each x 8 + the 8 channel thing+ mounting hardware= more money than the Mmux way to have equal. This is why in the end i went to Muxs each mux can run two servos cost is 80$ about+-. Keeps it Lego excepting the Mux. In toy robots that are 100% micro servos they are very light being made of purpous built parts of light weight things. So they can drive the Dofs with no need for full rotation since they are directly driving each.

Now your plan has most the weight off the bot, corded to the Nxt and power so you may be able to use direct drive. It so hard to say what will work and what wont since FEW have made one like it. (Lego-azimo{sp?} uses your idea no Nxt or power on the bot corded) in bipeds that are made of Lego. You may want to look at his bot as well since it has arms and a type of suffle legged design as well.

One thing I did with mucho testing of many designs of human joints made of Lego. The weakest link is the Knee by a factor of 2 once it goes past about 75 degrees. The knee as compared to the hip and ankle' ; takes 2x more revolution as well is most all movment example. A biped standing up right wants to do a deep knee squat. If all Dof are made the same or equal; to keep the bot upright the knee turns 2x time the rate of the ankle and hip. so if say you program the ankle and hip to turn say 25 servo turns to be where you want the knee is 50 turns. gear knee up to be equal in relitive motion( so it only need 25 turns and you get half the lifting power as well at the knee. I found this rather odd and tested many parts to breaking just to be sure. to keep ever move in sync the hip and ankle run at 50% power and the Knee 100% and it works as seen when X2 does the squat or splits or climbs steps. the more you bend a leg the harder it is on the knee. in early testing my bots knee would at full bend just stirp out gears or flex to much this creates instability a big issue in bipeds.

I do know this project will test your imagination as well as your knowledge

One thing about these type of projects be prepared to change what you think you will do alot. When you feel like its at a dead end, time to step back and view it from a-far. Even at times you may need an "other project too to give you a fresh perspective as well.

Doc "Will be watching this project from a-far "

[zemata]

Thanks for even more great info! I've been doing a lot of reading and research the last couple days and know a lot more about servos and what I need for my project.

All I really need to know now before I place an order from mindsensors is if someone can compare the speed and torque of their mini-servos to Lego motors (most of which I own) so I can see if they're powerful/fast enough for me. They look like a good size and have built in mounting for Lego. Also I need to know how much they can spin. What are their operating angles? 180 should be more than enough for me



Lastly here's some fooling around and rough sketching. Remember, I'm a mindstorms noob! I use NXT-G and am still reading tutorials and blogs!
http://www.youtube.com/watch?v=R-UcAPnJOj0

[zemata]

Here's the servos I have my eye on. http://servocity.com/html/hs-55_sub-micro.html
180 degrees and 1500usec compatible which is what the NXTServo takes. Correct?

So I compared the torque to some Lego motors. The website lists it as having a maximum torque of 18 oz.in, which, according to this http://www.magtrol.com/support/torque_calc.html converts to 12.7 n.cm. That's pretty decent compared to some of the older Lego motors http://www.philohome.com/motors/motorcomp.htm.

As soon as someone confirms my calculations I can order some servos and parts. I don't want to buy these things and have them be weaker than the red lego micromotor ):