Servo Control with Arduino

Help & Support Robot Parts
1

I’m looking to built a little Halloween decoration as my first robotics project. My current plan is to create an assembly that looks like lynxmotion.com/images/jpg/asb043.jpg with a foam pumpkin (1.2 lbs - hoping I can lighten that somewhat by carving it) on top instead of the gripper. The goal is to operate less like an arm and more like a reverse knee. When a trick-or-treater approaches, a passive infrared sensor triggers a sequence that will raise the pumpkin up, turn on a Larson scanner, and then reset to a “sitting” position after some period of time or when the PIR sensor goes low.

What I’m trying to determine is:

  1. Will the HS-422 servos be sufficient to lift the weight of a foam pumpkin with this configuration?
  2. Will I need a motor controller to operate the servos. I’ve seen videos on youtube showing servo control from an arduino without a motor controller but I know that a motor shield exists. I’m not sure in which cases it’s required and when it’s not. My guess is that I’d have to interleave the servo commands to get the platform to raise and keep the pumpkin level.
2

I will let someone else answer which is the best servos to use for this configuration. I am pretty sure that the HS-422 will not be sufficient for that much weight.

You can run servos on Arduinos using the Servo library: More details in the library reference guide. In the environment go to Help menu, choose Reference menu item, In the window that opens, click on Libraries, Then click on Servos…

The difficulty with this is that normal Arduinos are not set up with the 3 pin servo headers. Soon Lynxmotion will release a board that has servo headers :smiley:. There are threads about this in the forum, such as: viewtopic.php?f=48&t=7469

You can setup a normal Arduino to handle servos by either using a solder less prototype board, but there are issues like what to do to setup a power bus, and the like. I have seen a few Servo Shields as well. The one I have however does not use the standard Servo Library and has some other limitations.

Good Luck
Kurt

3

The 422 is not a very high end or powerful servo. I do not know the weight of the foam pumpkin so I can’t tell you what servos you will need.

4

In my original message, I mentioned that the weight was 1.2lbs, although I’m hoping I can lower that with carving out the interior.

5

I would recommend either the 755 or the 805 servos and brackets instead of the standard size servos.

lynxmotion.com/c-116-large-brackets.aspx

The standard sized servos with enough torque will be pretty expensive. The 805 and 755 are more affordable.

6

If you want to use servos and arduino, buy an Arduino Nano with its extension board.

I’m using one to pilot my Bicopter (twin-electric ducted fan) by mixing receiver channels with gyros and to issue command to the servo.

7

I already have an uno, but wouldn’t be averse to building an arduino board up from components. @Jim That’s for the info on the larger servos. Question: Am I going about this the wrong way? Should I be looking at hydraulics, pneumatics instead? Obviously, the parts can be re-purposed for other projects, but I’m wondering if I’m crossing a threshold for a hobby project. (Not that it would be the first time)

8

The 1.2 lbs should not be a problem for the larger servos. I wouldn’t know where to start with hydraulics or pneumatics.