Step 1: Got a micro-controller. Step 2: Need servos...

Ok, I started another post simply because this is onto a different topic in my construction. Ultimate idea for now is to construct a four legged walker with a camera, a few distance and infrared sensors for motion tracking and knowing when a wall is nearby. The child in me wants to stick an airsoft gun on it as well...

Nevertheless, I now have a UNO board with a starter pack with things to play around with, and I think I got a decent handle on how to operate various gizmos. Now I want to get started on my robot by making the four twist and lift servo combos that will rest at each corner of the "body" for the four legs.

Here are the supplies I'm looking at: Shield: http://emartee.com/product/41953/Sensor%20Shield%20V5.0%20%20Arduino%20Compatible Servo Possibilities: http://www.hobbypartz.com/37gexidised11.html http://www.hobbypartz.com/33p-solarservo-d222.html Pan and Tilt Kit: http://www.robotshop.com/lynxmotion-pan-and-tilt-kit-aluminium-1.html

I was planning on using the same servos on the leg's mid-joints, with metal legs, 3-4 inch segments. I'm not yet sure how much the body will be carrying, but it will have my camera (weighs probably 10g at most) the UNO and shield, metal chassis, at least 2 distance and 2 infrared sensors, battery pack. The airsoft gun is still optional, but will definitely be the heaviest.

From other opinions and research, I've been told that controlling 12 servos with the arduino board has a power issue, and am curious that it's the same way with a shield.

Anyone have any opinions on this? Thanks!

From other opinions and research, I’ve been told that controlling 12 servos with the arduino board has a power issue, and am curious that it’s the same way with a shield.

That doesn’t make much scense. You normally don’t power servos from an arduino. You will need a seperate power supply for the servos.

From other opinions and research, I’ve been told that controlling 12 servos with the arduino board has a power issue, and am curious that it’s the same way with a shield.

Controlling 12 servos should not be a problem, with or without a shield. It takes only a miniscule amount of current to tell a servo to move.

Actually moving a servo requires huge amounts of current, more than the Arduino can provide, with or without a shield.

Bottom line: The shield is not necessary for controlling servos and is of no help powering the servos.

Ok, sorry to make the statement vague, but PaulS response answered my question. Baiscally I just need to wire the servo’s powersource directly to an alternate power, via the battery, but wire the signal to the arduino. Would the shield be worth getting still for the sensors? Or does it just simply make pluggin sensors in easier? Mainly, if there’s any preformance boost, where the shield relieves the arduino of any processing or not, would I get one.

Anyone have opinions on the servo’s I picked out? They seem decent quality, but I’m not very familiar in the servo world.

Yes, you definitely cannot “power” the servos from ANY Arduino board, the Arduino
is only used to send control pulses to the servos. You need to power the servos
directly from a battery, typically 6-7.2V, but you can probably power the Arduino
board from the same battery too, if you add a bypass cap [0.1uF] and a large
electrolytic cap [100-220 uf] across the servo battery buss to filter the servo
motor noise.

Also, definitely [maybe] buy the sensor shield - as I indicated previously, it’s a royale
pain to connect servos to a standard Arduino bd. OTOH, you can plug them directly
into the shield.

HOWEVER, one caveat → I cannot tell from the info shown for the shields where the
Vcc buss power [middle row] on the 3-row headers comes from. If it’s the 5V Arduino
buss power, then forget it.

Also, I don’t personally like those RJ45 style connectors used for analog, and I have no
idea what they mean by “buckled ports”.

Just doing some quick back-of-envelope calcs (which may be wrong) - but it seems like your mass/torque budget might be blown; I don't think the servos will be strong enough (without knowing the mass of the chassis, batteries, arduino, shield, etc). You may want to run the calcs yourself, using your actual and best-guess numbers for the parts going into your robot.

Those servos are more or less identical in specs from what I could see; basically @ 6 volts they develop 6 kg/cm. Since you want, at minimum, legs with 3 inch segments (7.62 cm), that'll mean that at then end of one segment, the servo will be able to lift at most 787g. There will be 8 servos (@ 37g each) and 4 pan-tilt brackets (which I guessed each at about the weight of a servo, but I am probably off by a lot) on the body; a total mass of 444g...

You need to do these actual calcs yourself, since you know (or should have an idea) what your total mass (plus any extra for other "accessories") for everything will be. Once you know that, you can pick out your servos. I would seriously recommend using metal-geared dual-ball bearing output shaft servos for this application, as anything will likely strip the gears in short order (but it may be alright for initial testing).

cr0sh:
Those servos are more or less identical in specs from what I could see; basically @ 6 volts they develop 6 kg/cm. Since you want, at minimum, legs with 3 inch segments (7.62 cm), that’ll mean that at then end of one segment, the servo will be able to lift at most 787g. There will be 8 servos (@ 37g each) and 4 pan-tilt brackets (which I guessed each at about the weight of a servo, but I am probably off by a lot) on the body; a total mass of 444g…

You’re right that it needs calculating, but your figures seem rather pessimistic. You’ve calculated the worst case with the weight applied at right angles to the servo, but it may not be necessary to support that much deflection. You could also double the servo’s carrying capacity by preloading it in the opposite direction. On the other hand, it will presumably need to lift legs off the floor at some point which means the weight will be carried on less than four …

A practical thing to do is buy three of the servos and make a test leg to see if the servos meet your expectations. Otherwise you might research the quadrapods made by others and see what works in their designs.

Both of the servos you have linked have all plastic gears. For durability (avoiding a stripped gear) it's worth the extra money to buy one with metal gears. There's a lot of pressure on those little teeth in that final gear and all of the wear is placed on less than a third of those teeth.

Ok, new approach. A little costly, but it's not like I'm in a hurry for this thing yet.

I'm looking at this for the leg structure: http://www.robotshop.com/lynxmotion-aluminium-leg-pair-no-servos-brushed-3dofc-blk.html And this for the chassis: http://www.lynxmotion.com/p-435-quadrapod-body-kit-mini.aspx

I figure since they're the same company, they'd be more compatible than trying to jerry-rig my own thing. Plus, being a first project, figure I'd get a couple things pre-made than do everything from scratch.

I understand with the plastic gears, I played airsoft a lot and plastic gears were an assault rifle's worst nightmare. Luckily, the real ones in the army doesn't rely that much on them.

I figured since the chassis and legs would be coming from there, might as look into the servos from there as well, and I found these: http://www.lynxmotion.com/p-509-6x-hs-645mg-with-6-free-metal-servo-horns.aspx http://www.lynxmotion.com/p-293-hs-645mg-133-oz-in-standard-servo.aspx

They have abut the same speed and a bit more torque. My only concern is the cost. Total price of all those parts is about 600$... I don't really want to shell out that much for something that may now work the way I want it to, much less I still need to add things to it... I may revert to building an RC car by the looks of the pricing, but then again, I may be over my head with looking at these more expensive things.