Posted by Howard Gordon on February 13, 2008 at 11:31am
Big improvement in stability with the addition of a simple duct made from a sheet of 2.5mm RCF (extruded polystyrene) foam from rcfoam.com. The RCF is similar to depron that was recommended by another forum member, but somewhat more flexible and higher density. I was able to bend the RCF sheet to a 12-inch diameter, while a similar thickness depron sheet broke when bending.There is some yaw rotation at the beginning of the clip, but you can see toward the end that I got that under control, actually overshooting by a bit. Now that I have some semblance of control, it has become obvious that the current motor/prop configuration (CR2805 w/12" props) can't develop enough lift to get more than a few inches off the ground (i.e. out of ground effect), probably because there aren't enough windings on the motors (1430 rev/V), so I will have to return to the earlier CR2816 coaxial motor set, which weighs more but does have sufficient power.One other lesson which I mentioned on the forum - pre-flight inspection now includes a check that the electronics are secure. On the first test flight, the camera module worked itself loose and dropped onto the props -
Here's how things looked after I rebuilt the duct and replaced the camera (now secured with a cable tie)
I'd like to see it flying higher as well. I've changed the motors and now have to get everything rebalanced.
I could remove the camera board, but it's used by the software that is controlling the UAV. I'm actually getting a live digital video feed through the same WiFi connection that is relaying commands from the base station computer.
I really love what you do! I began a similar project using a gas motor. It looks like the honeywell UAV. I can't wait to see your machine fly higher. That is the sort of machine I want to build.
Keep it up!
ps- why don't you remove the camera when you test the machine? :P
Thanks for the link. I have watched various Coanda prototype videos and see many of the same stability issues I have wrestled with in my early test versions with the prop on top. My inspiration for this project has been the old Hiller Flying Platform video - https://www.youtube.com/watch?v=dmSCyy0_OX4 - which shows an inherent stability that is really attractive. I have experimented with coaxial rotor helicopters that achieve their stability with flybars, but at the cost of a lot of vibration, and I have experimented with quad rotors - in both cases, the exposed rotors scare me. With any of these projects, the "devil is in the details", and you just keep pushing forward.
I have been following the gfsuav threads for the last 6 months with much interest and see a recurring complaint involving the stability of the dish platform model.
It was also interesting to come upon your project and learn your views of the balance solution expressed so wonderfully in your analogy of a baseball bat being easier to balance with the heavy end on the top.
This may be of interest to the Coanda effect group since it seems counter intuitive at first and unfortunately not the direction they are following.
With the addition of your shroud, I can see the resemblance somewhat. The main difference being the use of the directed airflow to circulate over the shaped dish for the lift.
By coincidence, I was looking at http://www.gfsprojects.co.uk/ a couple of days ago. I have occasionally seen threads on Coanda effect saucers pop up on rcgroups, and did give them some thought. It's a cool idea, but I have some doubts about the power efficiency.
Anyhow, I'm headed back to the hardware store to get what I need to mount the larger motors. Though I've been tinkering with the coaxial approach for a while, it does seem like I have moved a couple of steps closer to something viable.
Fantastic resource for all aspects of telemetry , control and alternative propulsion methods.
From looking at your idea I was thinking that your more than half way. If you use the dish it would be interesting to see if you you get more lift with your power set?
If you have an interest there is a lot more interesting projects that Jean participates in.
Comments
I could remove the camera board, but it's used by the software that is controlling the UAV. I'm actually getting a live digital video feed through the same WiFi connection that is relaying commands from the base station computer.
I really love what you do! I began a similar project using a gas motor. It looks like the honeywell UAV. I can't wait to see your machine fly higher. That is the sort of machine I want to build.
Keep it up!
ps- why don't you remove the camera when you test the machine? :P
Jerome
It was also interesting to come upon your project and learn your views of the balance solution expressed so wonderfully in your analogy of a baseball bat being easier to balance with the heavy end on the top.
This may be of interest to the Coanda effect group since it seems counter intuitive at first and unfortunately not the direction they are following.
With the addition of your shroud, I can see the resemblance somewhat. The main difference being the use of the directed airflow to circulate over the shaped dish for the lift.
By coincidence, I was looking at http://www.gfsprojects.co.uk/ a couple of days ago. I have occasionally seen threads on Coanda effect saucers pop up on rcgroups, and did give them some thought. It's a cool idea, but I have some doubts about the power efficiency.
Anyhow, I'm headed back to the hardware store to get what I need to mount the larger motors. Though I've been tinkering with the coaxial approach for a while, it does seem like I have moved a couple of steps closer to something viable.
I like your idea and progress so far with a different take.
I am wondering if you have seen any of the development
using the Coanda Dish.
The link below is to a Frenchman's site, JLN labs.
http://jlnlabs.online.fr/gfsuav/index.htm
Fantastic resource for all aspects of telemetry , control and alternative propulsion methods.
From looking at your idea I was thinking that your more than half way. If you use the dish it would be interesting to see if you you get more lift with your power set?
If you have an interest there is a lot more interesting projects that Jean participates in.
http://jnaudin.free.fr/
I am interested in the electric lifter projects though I dont have a workshop safely kitted out to seriously witness it.
Cheers
Mike