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Hi, I'm planning to buy an Arduino UNO for a stair climbing robot (that will require high torque servos to 'lift' itself)

I am not so good in Electronics, can someone please clarify these doubts:

1) According to Servo specs, at 6V, the servo can provide (for example) 8.7kg-cm torque... but.. can I somehow achieve that torque on Arduino UNO ? - because it limits the voltage to 5V ?

2) Regarding the input supply power (in terms of Current or mAh), can I get the maximum torque with a 9V battery (because I think it has low mAh) ? - otherwise - do I have to use a good 7.2V Rechargeable battery with high ___mAh to get a good torque? - and what about those DC Adapters?

3) Would the maximum torque of each servo depend on the 'number of servos' I use? ..i.e. the power provided to each servo?

Any other related things that I need to know in order to work with High torque servos with UNO ?

Thanks !!
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1) No, you cannot power servos from the boards. You will need to supply the servo power form another source.

2) You will probably need to power the servos with heavy duty batterys or power supply. Under load, normal hobby servos can require 1a or more of current to be supplied for each one.

3) The amount of torque supplied by a servo will be dependent on the amount of current you can supply to it.
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3) Would the maximum torque of each servo depend on the 'number of servos' I use? ..i.e. the power provided to each servo?

Each model servo has it's own maximum torque specification. You must purchase the servos strong enough for the mechanical loads you will be giving them. And your power source must be able to supply the maximum current draw for all the servos combined. Plan on large expensive batteries, but battery selection can happen later while you build and prototype your project perhaps using AC powered DC output power supplies. Modified PC power supplies are an inexpensive source of DC power while designing, building, and testing projects.

Any other related things that I need to know in order to work with High torque servos with UNO ?

The Uno has no control or effect or limit on servo mechanical power, only the servos themselves and the current capacity of your voltage source is the system limits. The Uno will only be commanding the servos, not providing them with power.

There are literly hundreds of different servos avalible in all torque, speed and price points. Servo selection will be the most critical project decision you will have to make. Choose wisely grasshopper.  smiley-wink

Lefty
« Last Edit: February 26, 2011, 09:12:10 pm by retrolefty » Logged

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3) Would the maximum torque of each servo depend on the 'number of servos' I use? ..i.e. the power provided to each servo?

Each model servo has it's own maximum torque specification. You must purchase the servos strong enough for the mechanical loads you will be giving them. And your power source must be able to supply the maximum current draw for all the servos combined. Plan on large expensive batteries, but battery selection can happen later while you build and prototype your project perhaps using AC powered DC output power supplies. Modified PC power supplies are an inexpensive source of DC power while designing, building, and testing projects.

I would have to respectfully disagree with selecting the batteries after getting something working without batteries, especially a robot. Really, they should be selected as part of the design phase, if at all possible. You might need to do some test chassis runs or other experimentation to see what kind of torque vs. weight vs. current consumption is needed, then carefully design your chassis so that when you put on the selected battery, it works out properly.

See, the problem is you can get into this weird "vicious circle" where you need more current for more run time, but that drives up the weight, which requires more torque to move, which requires stronger (and possibly larger) servos, which require more current, which require bigger batters, which drive up the weight, which...

I think you get the picture.

The only way around this is to plan around it as early as possible - so you know what kind of battery technologies you can use for the run time, weight, torque and current requirements, etc in the final design.

/definitely not an easy way to solve this problem, on any robot - let alone a stair-climbing device...
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I would have to respectfully disagree with selecting the batteries after getting something working without batteries, especially a robot.

Well honorable people can disagree on this point I'm sure. However the battery is going to be a very expensive item and fundamental to the success of the project and until I actually had a chance to measure worst case current draw of all the heavy current consumers in actual operation, I would be uncomfortable selecting and purchasing the battery first. Possibly only to learn later during testing that it had too low a current draw capacity, or even to learn later that a smaller battery at half the price would have the current draw and duration spec I had in mind. I never 100% trust current consumption specs for many components. Or as Regan said trust but verify.
 
However your way may work better for you.

Lefty
« Last Edit: February 26, 2011, 11:22:34 pm by retrolefty » Logged

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