
Noobot
Canada
Asked
— Edited
I have recently bought the EZR kit, but the servos only rotate in a circle. I have since learned that there are things called solenoids which don't rotate but move linearly like a pogo stick. I can't find them here. Are they available?
This is just one source....but I am pretty sure solenids require an H bridge much like DC motors....You coulkd make a "linear activator" with a fine threaded rod and a modified servo!
One problem with solenoids is they get hot when held in the energized state or used a lot. If you use a solenoid you must also install a blocking diode across it's two power lugs in the proper direction. If not a voltage spike will slam back into your control circuit and destroy it.
irobot58 is also correct and has a great idea about using a threaded rod and a Servo. That may be a lot easer. ARC does a great job controlling servos.
A lot of these "ideas" we have have, have never been done with EZB. They usually reside in our heads however I'm sure other robot clubs have used these building ideas. EZB is a new platform being only a couple years old and evolving and growing all this time. Look through the projects on this web site and others to see how others have built there robots. You may see something that could help. I'm sire if someone scan help they will post some pics for you.
Good luck and keep in touch.
Here is an example using a MOSFET. (Our favorite thread)
There was a lot of discussion about using TIP120 which is nearly the same functionally but the mosfet uses less power. I googled the above image but edited the EZB block in.
On and Off switch
Noobot, just remember that the diode is required for ANY device which uses a coil (inductive motors and solenoids) but otherwise you wouldn't need the diode. The problem Dave mentions is due to the magnetic field which is briefly present after the current is removed. The magnetic flux lines pass through the coil as the field collapses. That induces a brief voltage spike. The amount of voltage varies with the coil size and the amount of current but it's truly irrelevant since it's most certainly too much for logic circuits to handle. This circuit and others give a safe path for the excess current when the coil is shut off.
EDIT: OOPS he beat me to it.
Btw linear servos do exist if that's what you're after. Here is a conversion kit for a standard servo. This will give you more precise control than a solenoid however it doesn't have the speed a solenoid has. How will you be using it?
I own some pinballmachines and know solenoids, most solenoids in pinballs will only akt for a short time, except the flipper fingers, but there is a little trick....if you press the buttons the fingers have much power because they are activated by the power-coil and switch to a smaller coil that is for holding the finger in position.
This trick will be used, because the powercoil would burn when it's activated to long.
You can use linear servos (look at ebay) or use a other relution.
Can you tell more about the projekt?
Is it really required that buttons will be pressed, or is it possible to solder some cables to the switches that should be pressed and switch them directly with a transistor or relais?
Marc