so my senior design group at UCF needs some help with the electrical engineering aspect of our project as we are all ME majors and lack confidence in this area.

Our design is driven by a DC gear motor that has been geared down to rotate at 0.9RPM. From the motor is a rotary shaft that is 9" long and 1" in diameter and will rotate the system from 0 degrees to 90 degrees and from 90 degrees back to 0 degrees in the XZ plane. At each of the two positions (0 and 90 deg.) the system needs to remain locked in that position. A plate attached to the rotary shaft with a diameter of 3.5" has 2 holes for the pull solenoid to enter and hold the system. With the integration of microswitches that are timed to power/unpower the solenoid is able to lock/unlock at the required times/positions. The shaft will have indents that push the microswitch buttons in and out at the appropriate times. While the system is moving from one position to the other we need the solenoid to be powered on and the motor to be powered on. Once the system reaches one of its locking positions (0 or 90 deg) the motor needs to power off and the pull solenoid needs to power off and drive itself into the locking hole thats on the plate attached to the shaft (a spring on the solenoid shaft will allow for this motion once the solenoid is powered off).

We are planning to us a DPDT switch to power the system and allow the DC motor to be reversible.

Our groups main struggle is how to wire the system as a whole and also how to time the system so that the motor does not power up simultaneously with the solenoid because that situation would jam the motor up and also put to much force on the pull solenoid to be able to pull out of the locking hole. Another concern would be the motor powering off simultaneously as the solenoid shaft enters the locking hole.

In summary, locked at 0 degrees our system will unlock (pull solenoid powered on) and motor power on and move out to the next position of 90 degrees. Once he motor drives the system to 90 degrees the solenoid will turn off and the spring will drive the solenoid shaft out and into the locking hole on the rotary shafts plate. At the same instance, the motor will power off. From here, the system needs to repeat the process to move from 90 degrees to 0 degrees and lock again. The time that the motor takes to move from each position is 25 seconds.

Hopefully this is not to confusing in words....all help is greatly appreciated and let me know if I can clarify anything to help!

  • \$\begingroup\$ Sounds like a single disc brake mechanism would work better, rather then using a solenoid pin that can become jammed. \$\endgroup\$
    – Nedd
    Dec 6, 2015 at 1:22

1 Answer 1


You might place a micro-switch at the far end of the solenoid pin's throw. The motor enable signal then passes through the normally closed contacts of that micro-switch. As a result the motor cannot start up until that micro-switch (and the solenoid pin) disengage. Similarly, the motor stops the instant the micro-switch (and the solenoid pin) re-engage.

Similarly, you could detect the opposite side of the solenoid pin and use the normally open side of the micro-switch contact. At that point you are guaranteed that the pin is fully out of the way.

It may also help if the solenoid pin and the mating holes had a tapered shape. This could reduce the tendency of mechanical jamming (and even provide some self aligning) of the moving parts.

  • \$\begingroup\$ Nedd, love the addition of the microswitch to come into contact with the pin and disengage the motor at the required times. Thanks so much! \$\endgroup\$
    – UCF_MechE
    Dec 6, 2015 at 16:11
  • \$\begingroup\$ If that seems to solve the issue click on the Accept to close out the question. Good luck with the project. \$\endgroup\$
    – Nedd
    Dec 7, 2015 at 7:04

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.