We are a group of Uni students tasked with making an automated CPR device that performs CPR on an infant dummy. We are looking into what we can use to perform the compressions. We need to have a compression length of 4cm, and are unsure of the force requirement but are assuming around a minimum of 40N. We have 12V to work with. We have had an idea to use a solenoid such as your large push-pull solenoid however are unsure as to what the ‘starting force’ means and whether it would be adequate to do the job. We would greatly appreciate your opinion and any other ideas you have on how we could make this work.
Cheers
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Hi Jess,
Welcome to the forum 
The force on the armature of the solenoid will change during the solenoid’s stroke/throw. Some solenoids will decrease from their starting force and others will increase.
There are a number of other factors that can contribute to the force as well including: temperature, duty cycle, magnetic saturation, the shape of the armature, and length of the throw. Typically industrial solenoids will be characterised by a force curve plot which shows how the force varies with all the numerous factors.
There’s some good discussion in this thread which goes over some of the factors in more detail.
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