# Servo motors

1. Dec 2, 2006

### guru

I am building a small satellite for my project in which I have to release a mechanism to eject the landing gear at a certain altitude before landing vertically. The landing gear will consist of spring-loaded rods, initially at 90 degree angle with respect to the circular base of diameter 2 inch. Each spring is going to be connected to a small metal piece.
I'm thinking of using a servo motor to detach the metal piece before landing, so the rods will extend.
What kind of servomotor will be appropriate for my project? Where can I find more info on servo motors?

2. Dec 2, 2006

### Danger

I would actually recommend a solenoid rather than a motor. If I understand your set-up correctly, it would be essentially the same as pulling the trigger on a gun. A solenoid will easily retract the sears (retaining lugs) to allow the springs to deploy the gear.

edit: You could achieve the same end with pyrotechnic charges, compressed air, etc.. But the air thing would still require a solenoid to work the valve.

Last edited: Dec 2, 2006
3. Dec 3, 2006

### guru

solenoids?

Thnaks for your suggestion. However, is the soleniod capable of interfacing with the microprocessor (BASIC Stamp). What type of soleniod will be appropriate and where can I get more info.
Obviously I have no experience whatsoever in design....this is my first

4. Dec 3, 2006

### Danger

I'm afraid that I have absolutely no idea of what 'Basic Stamp' is, and no knowledge of microprocessors. If it can drive a motor, however, it can drive a solenoid as well.
As for what type of solenoid, they're all pretty much the same except for strength and power requirements. If it's a really light load that it has to pull, check out a hobby shop for units that move track switches in a model train system. You could also use one that pulls in the Bendix in a car starter, if you need a lot of strength and have some good batteries on board. There are all sorts in between those extremes.

5. Dec 3, 2006

### FredGarvin

The solenoid sounds more like the correct route. You don't need a variable positioned part (which is what a servomotor is really for), just an on-off. You wouldn't directly connect the solenoid to the IC. You would use the IC to control a relay which would then provide your switching for the solenoid. I guess that does all depend on how large of a solenoid you would need, i.e. forces involved.

6. Dec 5, 2006

### guru

Sounds like a great idea. But after doing a little research, I still have no idea how relay works and how its going to interface with the microcontoller and solenoid. Any help will do.
Thanks !!!

Last edited: Dec 5, 2006
7. Dec 5, 2006

8. Dec 5, 2006

9. Dec 5, 2006

### guru

those were really good sites. I now have a good idea how relay works. Most of the relays I saw on the internet were rather huge. Do they have very small ones? It really won't be easy to do the interfacing, but am willing to explore my options.

10. Dec 5, 2006

### sas3

11. Dec 6, 2006

### Mech_Engineer

Since you mentioned BASIC Stamp, I thought I'd jump in and let you know that Parallax makes a Servo Control Board that interfaces with their main boards quite easily, and can handle servo control independently. Just send a command and the board handles the rest.

I realize that a solenoid is essentially what you want, but servos are so cheap and easy to implement in this setup, I say why not. Just make sure the servo has a torque rating that is sufficient for your application, hobby shops carry heavy duty metal geared ones (for use in RC cars, but their control structure is the same) if you need more oomph. You can have a fully programmable system with full individual servo control and a couple micro servos for under $200. It would also be quite easy to add buttons, LCD displays, and sensors to your package for a little bit more. For little tinkering and custom robotics and hobby projects, it's hard to beat the expandability and price of the Parallax stuff. Basic Stamp 2SX Module ($59.00)

BASIC Stamp Super Carrier Board ($19.95) Servo Controller ($39.95)

Parallax Micro Servo (\$15.00 ea.)

Last edited: Dec 6, 2006
12. Dec 6, 2006

### FredGarvin

Great post ME. I hadn't realized that they had come down in price so much. I think that would be easier in the long run.

13. Dec 6, 2006

### Mech_Engineer

Yeah, the Parallax stuff is so cool and easy to use (as in you don't have to be an EE to figure it out). All of their available expansions are really cool too, they even have a bluetooth module to add wireless control from a computer.

Poking around their site, I found this one too: http://www.crustcrawler.com/

Turns out, they have advanced hobby robotics powered with the very same Parallax stuff I mentioned. In the future I may end up buying one of the HexCrawler HDATS kits, paired with a video camera and bluetooth control, it would be a very cool off-road rover! Add some sensing equipment and gps and it would practically navigate itself