I am building a wall climbing robot using suction. The suction will be provided by an Electric Ducted Fan(EDF) attached to a motor. I have estimated the total weight of all the parts of the robot to be around 700 grams in weight. My main problem is how do I calculate the suction force given to me by the motor and what is the maximum weight it can hold. The motor I am using is C20pro 3800kv with the following specs.
@ 10v @ 11.1v @ 12.6v
Current: 29.6A 34A 39A
Thrust: 24.8oz 28.9oz 33.3oz
Power: 296W 377.4W 491.4W
I was thinking of using 11.1 V (3S LiPo batteries). The fan of the EDF is 70mm is diameter. Can you suggest how I measure the suction force and how much weight it can hold when vertical? Also, I don't quite know how to interpret the value of 'Thrust' in the specs shown above. Sorry, I am only starting out with robotics and this is only my second project. Would appreciate any help. Thanks.
Hi, I think you are going to have problems with you type of fan for a start, these fans work efficiently when there is air flow through them.
You are aiming to stall that air flow by plugging the inlet to develop a low pressure area.
This fan cannot do that, block the inlet and its efficiency goes down and it will not provide any low pressure area.
"THERE is no such thing as suction" Prof Julius SumnerMiller
Quote from Australian TV show "Why Is It So" circa 1968 or there abouts.
One of the many things I remember of a great TV series.
There is such a thing as high and low pressure, and vacuum.
Sealing against the wall is also a problem, what are you going to use?
You will need a pump to get the low pressure you require.
Did you include the battery mass in your calculations because they are going to have to be large items to supply 30A at 12V.
700gms is a bit low.
You better go back and review the physics of your project.
Firstly thank you for your comments. Much appreciated.
I got the idea for this project from this video: Suction car robot "Ibex" from Operative RC - YouTube
I plan on a 3mm gap between the fan and the wall.
Do you have any suggestion for the battery that I can use? A LiPo battery perhaps? Also any idea on how I can calculate the force (weight) it can hold ?
There will be so much inefficiency in the airflow that I doubt if there is any easy way to estimate the suction effect apart from trial and error. You could probably influence the effectiveness a lot by changing the shape of the duct feeding air into the fan - avoiding sharp corners, for examples. Following on from what @TomGeorge said more airflow is probably better than less.
It's an interesting gadget, but there's a way to go before it can be a silent "spy-on-the-wall"
"Suction" does not create any force. The force is created because the atmosphere outside the suction cup is pressing towards the wall with a greater force than the atmosphere inside the suction cup.
The other thing you need to think about, is that the force is a horizontal force. To defy gravity you need a vertical force. This actually comes from friction between the wall and the robot.
What they are doing there, is creating a thin layer of rapidly moving area between the cart and the wall, which has a low pressure. That is a bit different to trying to create a vacuum. I suggest you try and copy their device.
