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[SKATEway]Post 8

Hello,

As says Alban, our project is currently suspended by th teachers.

We are waiting for the final decision. For the moment, I am redirected toward another branch.

Charles.

 

 

[SKATEway]Post 8

Hello,

Unfortunately the end of the week was as productive as the begin. I have not enough time to keep the project above the surface. I am currently in a compressed work week with three exams. I know it’s not an excuse. So this week in addition to the challenge, I only order this IMU 6 Degrees of Freedom to test the angle capture.

Charles

[SKATEway]Post 7

Hello,

The beginning of this week was not very productive, because I was in the country side for holliday.

So the next step is to purchase the IMU as soons as we can to test  the algorithm which provide the angle. So plan to let the IMU on the ground and notice that there is no gyroscope drift and also move the IMU to check if there is the right value.

We have to begin our PCB and determine the motor because the last motor we choose was wrong.

Charles

[SKATEway]Post 6 UPLOAD

Hello,

Here the diagram with more explicit anti drift.

Charles

[SKATEway]Post 6

Hello,

This 3 days I essentially worked on the diagram bloc to self balance our board with a null angle to the horizontal.

Its a simple PID but we have to add some stuff to make the regulation working. First we need to prevent the wind up on the integrator when the output is satured. Then the D componet increase hight frequencies noise. So we attach a low pass filter. FinaLly we have the value to apply on the motor. The board move to an other angle. Perturbations can emerge. Like the ground slope, the wind or humans. We got the final position now. We need accelerometer and gyroscope output to calculate the new angle of the board to the horizontal. We can directly use the output of the accelerometer but we have to apply an anti drift filter to the gyroscope output to cancel the integrated error over the time. Then we compare the request angle with this angle and do the operation again.

Here, the diagram bloc !

Charles

 

[SKATEway]Post 5

Hello,

I studied the most part of algorithms. And we will probably use the PID. It is the simple and the most appropriate for our application. Other algorithms are for more complicated functions, and have a longer process.

The PID is divided by three components. The first, P, do the most part of the job. It provides a proportional work according to the error. But with the P component only, we can’t search the final value. The system would be regulated +/- arround the control. To fix it, we add a I component, to integrate the error over the time to enable the convergence. Finaly, to increase the speed and the stability, add the D component, derivative.

I also see how to get an angle using accelerometer and gyroscope together. We cant use neither one, nor the other alone because we can’t have trust in their. We need to mix their output together. I saw two way to do. The first that we are more confident about the accelerometer and the second that we are more confident about the gyroscope.

The next step of our project is to buy the main stuff and to balance our SKATEway unladen.

 

Charles

[SKATEway]Post 4

Hello,

This week we got a scolding for our teachers because we have not worked a lot so far. We have to stand up and move on.

Now we have to concretize the choice of sensors and study about the regulation of the system.

On my side I will study about regulation. We already know we will use a closed loop because the output feedback on the system. Learn what is already existing. Chose several algotithm PID, SS, SIMO, MIMO, RST, LQR. Then determine the number of instruction to estimate the worst execution time of the loop, and the system’s response.

I know PID is the simple but not the more efficient, to be seen.

Determine what is the input of the regulation, an angle (not necessarly null), a speed. Think wich angle will we use. Absolute horizontal or about the road.

Charles

 

 

[SKATEway]Post 3

Hi, from now we have to post Wednesday and Sunday for more follow up.

We finally have all our component except the micro-controller. Motors are not final too. Because it is hub. It is compact but not necessarily enough powerful.

For the moment we have :

We are waiting for the teachers agreement to begin our PCB.

Sincerely,

Charles

 

[SKATEway]POST 2

Hello every one!

So the challenge of this week was to finalize the choice about batteries and motors. And we did it. First we did again the motors calibration we need for our system. Last week we did simple calculations. Taking all parameters, we conclude that we need two 450w 48v motors. Plus, we choose a hub motor to the gain space. We had to be aware about the function of the engine. We made sure it is a two direction motor with the good controller. I contacted the seller and he confirmed this fact.

Here motor + controller : https://www.aliexpress.com/store/product/8-inch-450W-48V-brushless-non-gear-hub-motor-electric-scooter-electric-motor/1461770_32476560207.html

For batteries, again for gain space, we found batteries kit to build by ourself. One more avantage, its less expensive. LifePO4 48V 15Ah (http://evcomponents.com/diy-battery-kits/48v15ah-headway-lfp-battery-kit.html).

For the next week, finish the list of composents (accelerometer, board, led …). Begin the PCB of our system with Expedition PCB that I installed this weekend.

Have a great week!

Charles

[SKATEway]POST 1

Hello,

Once week after the beginning. Here is where we are.

This week has been used to fix the system’s calibration. In the last post, I determined some values, but I based them on existing projects. I made calculs by myself for more accuracy from existing data such as acceleration (a = 2 m/s²),  total weight (100 Kg), spoke of the wheel (r = 0.11 m), rotation per minute (63 ras/s) . To extract resulting data such as couple (C), motors power (P), 48V batteries intensity (I).

C = a * m * r = 22 Nm

P = C * w = 690 W

I = P/U = 15A

The coming week, will be used to identify exactly what components we would use. The main challenge would be about motors and batteries. For motors, hub or not? A hub is space gain but the power delivered by the engine is less than a classic motor. The space is also a problem for batteries. We have to find the most flat as possible. We have to choose betwen several kind of batteries (lithium, lithium-ion, lithium iron posphate, lead …) We need to determine the need. We must not oversize our system because the battery is the most expensive item of the project. If a simple lithium battery is enought, we won’t pick the last lithium iron posphate generation battery.

Ps : A picture to visualize our SKATEway (made by my mate Alban)

rose_1v1

Charles