I am working in a project with a group of people and part of our design involves pulling back a platform connected to a spring. This platform has to be able to be pulled back different lengths. We have two ideas on how to do this: 1) Have a gear strip that is in a fixed position. Have a motor that turns a gear attached to the platform, this motor is attached via a gear to the gear strip. The motor will pull back the platform. The motor will be attached to a wheel which can rotate in order to engage and disengage the motor. This will be controlled by another motor. The main problem with the design is we do not know how well it will work when engaging, and diisengaging, whether the wheels will get stuck. 2) Have the platform attached to a linear actuator which can pull back the platform, this actuator will be attached to a hook that can be hooked onto the platform and disengaged by a motor. The main problem with this design is cost. I am looking for advice for which design is better, any possible shortcomings of the two and if there are any improvements or additional designs you can suggest. If the designs are not clear please ask for clarification.