RotaryRacer wrote:
Jdpber wrote:
Been doing som physics this evening calculating the gas strut force needed for the ski locker hatch along with the new engine hatch. I think I have a set of 60# struts in the shop. And the ply is 75# I'm estimating 5# cut off, 20# resin and glass added. 5-10 of foam and vyinal. So around 100 so let's call it 130 to be realistic and safe margin. So I'm thinking dual 60-80s would do the job. But I will not know till built.
You have to be really careful with the angles and stuff when calculating the forces required. When the lid is down you typically have a very short moment arm and a lot of force in the horizontal direction. In some cases the gas spring could actually go over center and try to hold the lid down. That is not a bad thing in some cases. But when you are trying to lift 100#, getting the springs to help all the way (especially when it is down) is a big help.
Also, most inexpensive gas springs have a very wide tolerance on their force. I'd plan on them being as much as 20% lower than the stated force. Also, there is a wide range of damping that will affect how quickly your can raise the lid or how quickly it falls.
When you are trying to hold something that is 100# open while you work on an engine and if that something should fall on you it can do some real damage. Stabilus, Suspa and other gas spring suppliers have springs with locking mechanisms that may be a good idea to consider.
yea physics was on of my fav subjects in college. IF it was not for girls and fun i would be a mechanical engineer now. Laitly i have been thinking of going back to school for ME degree.
i have a source in state that i have used many times and he has some very dependable struts. We have been very pleased with the 50 or more that dad and i have purchased over the past 10 years.
AS FOR holding the weight up. YES the stability and strength of the strut to hold the weight is key.. And i will not know for sure until i put an actual scale under the hatch in place finished and find the true center mass force that it is producing. But i can ball park it fairly well and go over 15-20% as i have done. I will test with a set of struts that i have that were too strong for the last hatch and go from their. Those struts will most likely be my "Set Up" struts.
TODAY i am looking at strut mounts and choosing what i want for the ski locker. Clean and simple is the plan. I already have mounts for the rear hatch.
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Not Penny's Boat
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