[CyL3D] Rethinking the motor

We had a long discussion with a student from SpiROSE (last year’s project with a rotative LED panel). He told us the problem they faced with the motor and ESC (Electronic Speed Controller). They could not get a constant speed output from the motor because the ESC was overheating, causing a shutdown and a boot up. It was caused by the motor asking too much current. The motor was one the had on hand and not perfectly fitted to their use. It was rated at 2100 RPM per Volt. While turning at 1500 RPM the ESC pulled 5A on 12V from the power supply, the same 60W would go to the motor, but to rotate at 1500 RPM it only needed 0.7V so the output current from the ESC was closing in on the max output, which caused overheating.

So I am looking for a motor  with a lower RPM per Volts constant. I reckon a motor at around 500 RPM/V would be suitable for our project. For now I have have settled on Turnigy Aerodrive SK3 – 4250-500kv Brushless Outrunner Motor from HobbyKing. 

Another problem was to convey the power through the axis. They had to scrub the anodising paint from the top of the motor to make a connexion to a ball bearing which was connected to the motor shaft. I would like if possible to stay away from passing to much power through the ball bearing as it can cause sparks and damage the balls. To replace this connection I am looking toward brush slip rings.

[CyL3D] Motor’s First Turns

In order to determine how much current the motor pulls, we had to make it turn with a load and monitor its consumption. The perfect load was in hand, we took last year’s LED pannel, as ours will have approximatly the same weight and dimension, therefore giving a good estimate on our power consumption.

We took the same brushless motor as last year, a MEGA Acn 22/20/4. Which is connected to a motor controller, a EZRUN Max 10 SCT. It is rated to be able to supply up to 120A, so we could not take this value to size our power supply.  So I tested the whole system to see how much would it drain.

First I had to understand how the controller worked. The datasheet is not very helpful, as it only says to put a RC receiver on the input wires. So I emulated one with an arduino. A RC receiver uses PPM signal, and is waiting for a 1 to 2ms pulse every 20ms. 1ms being the command for neutral throttle and 2ms for full throttle.

In order for the motor controller to acknowledge that you sent a RC signanl, you need to start by sending neutral throttle command. It is a security measure to prevent the motor turning on when it has just been plugged in. 

After came my first attempt with no load on the motor. It ran fine and the controller pulled around 1.5 to 2A. Then Itried with last year’s pannel, and it would not start rotating at the lowest speed, or be all jittery. My teacher told me that last year, in order to start the rotation, they sent a high speed command and backed down to lower one when it started. I did so and now the whole structure is rotating.

LED pannel rotating.
Slowed down 16 times.

I filmed it slow motion to be able to determine the speed it’s rotating at. With the almost lowest setting it is rotating just under 20rps. At this speed it is pulling 4A under 12V. I tried making it rotate faster, so I just left it at the high speed command I use to start it up. I did not go well. Leaving a high speed command made the controller pull more than 20A because it was unable to match the requested speed. So the power outlet shut down.

In order to get the whole system to high speed I proceeded gradually. Letting it establish at low speed for seconds and increasing the speed slowly.

An other problem rose up, at low speed it was not that wobbly. The structure was only a bit unstable. At high speed it is a whole different story. The metal structure would move around the table and produce more noise. We will have to be very carefull about the placement of the component and plan to be able to put masses and the lower rotating part to balance the whole structure, as you would on a car tire.

[CyL3D] Motor Controller (Help needed)

We are taking the same mechanical parts as last year’s project. Now we are trying to get how much currennt the motor pulls in order to get a proper estimation of the consumption. 

I ran into a problem while testing the motor though. I don’t know how to use the motor controller (which is a Ezrun max 10 SCT). So I went looking for the documentation and found the very extensive 🙂 doc which just tells us to connect a receiver and everything should work fine. On our side we are trying to drive it with an arduino or something alike.

So far I know that the controller is driven by a 5V PWM, but I haven’t been able to make it work. So I would love to know how last year’s group made it work. 

[CyL3D] Simulation and Dismantlement

Simulation

While Paul worked on producing images that are going to be displayed on our system, I used Processing to create a simulation of the rotating LED pannel. Processing is a Java based language made for easy visualisations. My simulation is able to load an image and then works simillarly to the LED pannel. It displays a slice, rotate a farction of an angle and displays the next one. Even if it is only showing a single image for now, it should be straightforward to change it to show a video.


Here is an image of two cubes made by Paul.

Dismantlement

As we are using last year base, I dismanteled their project to find the inner working of their project. We knew that the power was transmited the revolution axis, but we were not sure how the connexion was made.

It turns out that a wire is connected to the top of the case of the motor, so to go through the axis the current needs to travel first through a ballbearing. We then learned that it did not make a perfect connection so the voltage would be unstasble. To counteract this problem we will use capacitors and also raise the voltage going to the rotating part in order to lower the current.

[CyL3D] Power setup

During this week we have mostly focused on determining the architecture of our system. I have tried to look at the different power comsumption, and the solution to supply energy to our system.

Using the same structure as last year’s project, wehave decided not to change the flow of energy. No power supply will be carried on the rotating part. We will use the axis to carry the current. From the bottom part, we will input power, voltage to be determined. The top will be grounded, as will the whole structure.

There is a lot of energy to be supplied to the system. First of all the 1200 LED, then there are the controllers, the fpga, esp32, and many more power sucking devices to be determined. But for now all that we seem to bring on the rotative pannel seem to work on low voltage, 5V or lower. The problem resides in all the current our component will drain. For now I’m thinking about hacking a computer alimentation bloc. Some give out 500W (which might be overkill) in three different volatges, 12V, 5V and 3.3V. 3.3V might not be of use but 12V can be use to power the motor underneath the pannel.

There is still much researched to be done, we will focus on that this week, having a set list of components so that our project can really take of.