Having seen a vast improvement in the Arducopter handling when vibration was reduced I decided to experiment further. I thought it was worth trying to soft mount the tubes so cobbled together a test frame on a bit of 4x2. The 12mm tube mounts are held in place with ‘o’ rings. The video is with standard 75 shore rings 17mm ID. This was just the first test so was quite pleased but will experiment with other types/sizes.
This method will probably only work on a ‘H’ frame where the motor lift balances out.
Comments
Dont suppose you saw the end result. Extremely low vibration values, no jello with direct mounted camera, crash survivability, twice the yaw rate of other copters.Original idea taken to a successful conclusion. Come on.
Guys, I just use regular quality scissors. It helps a bit to sharpen them on a course stone block so they feel a little jaggy. Also I often tape where I am going to cut and then cut up the middle of the tape. Its still not that easy though and you have to chomp away for a while. I guess I can do about 10cm a minute.
I always laminate with a hair dryer in one hand and a squgee in the other. A quick pass with the dryer will make the resin very runny and it will soak in quicker.
The problems with Kevlar dont stop there though. If you have to sand, cut or drill it will leave a very scruffy edge. I will only use it in future to ad plies between layers of carbon to make a thicker laminate. Its good for that.
I did this last project with it just to use the last of it up.
Oliver, I always use vacuum with foam, no probs, but not light white foam, it will crush.
Joshua, Vaccum is great and if you are working on a solid mold (not foam), heating the whole thing while curing provides even more resin penetration, like an autoclave! Not easy to do at home.... Still, regular lamination methods yield and incredibly strong result. Have fun!
Thanks Olivier,
What's this "Google search" you're talking about?
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How embarrassing, of course it's that simple, and they're not even expensive.
I did make a few test pieces with ugly edges, and you're right about needing to work the resin in. I'll be vacuum bagging for sure!
Joshua, there are special scissors for cutting Kevlar, the blades have a specific angle and when you use those, you will be amazed, it`s like cutting regular cloth. For even better results, sandwich the area you want to cut between two boards, this will prevent the fabric from moving around as you try to achieve a straight cut.
Do a google search for kevlar cutting scissors
Another thing to keep in mind with carbon kevlar fabric is that the kevlar is reluctant to absorb the epoxy or polyester that you will be using. You need to make sure your resin penetrates properly to soak the fabric. You can always wipe out the excess before it sets. Apply resin prior to applying the fabric, apply resin on the fabric then add another coat and force it in there with a roller. It`s tricky stuff but it`s well worth it. This stuff is indestructible.
Vince, I bought some carbon/kevlar weave to remake the front of a Raven for a camera gimbal quite a while back, and pretty much just shelved it after trying to cut that fabric : /
I would like to get back on it soon, however. What method did you use to cut the cloth, rotary cutter, scissors? My sharpest TiN scissors just squished it around leaving a very ugly frayed edges, very frustrating.
You make good progress friend, I hope you get that adverse yaw figured out. I'm intrigued by your idea of changing the rotor directions.
Im in UK so prob not much help.
http://www.easycomposites.co.uk/
I wont be buying Kevlar anymore. Its such a pain to work with.
Hi Thomas.
All good info thanks.
I did put a post somewhere (Mission Planner forum?) asking if we could highlight parts of a graph and get statistical data.
My test was not that scientific but I was just proving to myself that the o-ring mounts were worth taking further. I will use the APM to get good data when its flying. It would be nice to have a league table of 'good' and 'bad' vibration measurements. The phone program I was using gave a vector total vibration but Im not sure the APM will go that, just separate axis.
I think almost everyone misses the trick of using the battery mass to dampen vibration by just hanging the battery loosely below.
I will clamp it tightly just above the APM and will try some 5mm 'special' foam to mount the APM on but have seen it cause more problems in the past.
There have been comments that my 4008 type motors have weak shafts and that any prop ground contact will cause a bend. I think some of mine may be slightly off so will replace with hardened ground shafts.
Expect to be flying in the next day or two.
I found that my traditional open ‘X’ frame was getting splattered with mud and debris and is very difficult to clean. I thought it was just a cosmetic problem until one ESC failed. On examination it was very wet inside the plastic wrap. It started working again after being dried out.
I expect tuning will be like a normal ‘X’ except it may need slightly higher gains in pitch due to the increased inertia around that axis.
The shell will be of Kevlar/carbon around a ‘lost foam’ mould. It doesn’t produce a nice surface (without a lot of finishing) but Im not bothered. Hope to start that today. The ‘airplane’ shape fuselage is just to help with visual orientation. Some people think the 5.8G FPV interferes with GPS so they will be at different ends. I do intend to put legs on it when I attach the camera gimbal.
It probably would be easy to make the booms quick release but Im not bothering this time.
Am in a hurry to finish so I can try 2.9!
Good looking project Vince. I've said before, multirotors are ultimately just a packaging exercise and the traditional hub and spoke frames are a bit tight, especially when one is trying to separate video Tx, RC Rx, data TRx, GPS Rx, power supplies, ESCs, batteries, etc. It's amazing any of these things work at all!
Have you considered making the motor boom quick release or rotate to facilitate ground handling and transport? I have vowed to only make folding frames in some type of H config for all my future projects.
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