The client requested a robotic rotisserie. The rotisserie had special features that made it unique among the other similar products. The product had such sophistications that turned it into a robotic design instead of a home appliance. The final design took about 4 months to get completed.
Also, since the product was supposed to be used in camps and parks, it had to be capable of working with a car battery.
1. Due to the complexity of the design and the changing requirements during the course of the design, one of the main challenges was the mutual understanding of all the details as set by the client. The changes caused a lot of communication with the client to come up with a final understanding.
2. For cooking all types of meats, a user-friendly configuration set up for different timings and temperatures had to be considered.
3. Considering the wide variety of consumer cooking tastes, the product had to be flexible enough to cover all spectrum of demands such as providing the consumers with the flexibility on how they wanted to rotate the meet.
4. Choice of the proper sensor was another challenge. The needed sensor had to meet the following conditions:
a. Ability to work at a high cooking temperature outside and inside the meat
b. Having a good temperature resolution
c. Linearity of the sensor’s output voltage vs the temperature
5. The other challenge was non-linear nature of the voltage produced by different temperature sensors.
The design was proceeded according to a scheduled plan. For each of the above challenges, their corresponding solutions were discussed and implemented as follows.
1. In order to overcome the changing design patterns for the work, after extensive discussions with the client who was himself a highly skilled mechatronics Ph.D. student, we reached an agreement on the basics of the design. Based on our agreements, a detailed Memorandum of Understanding (MoU) containing all the requirements of the client was prepared and agreed on. Also, in order to make sure that all in-work design modifications were included, at each step, the design path was reconsidered and discussed with the client. This procedure was an essential part of the successful completing the project.
Also during the course of the work, such issues as the block diagram, electronic design, PCB design, firmware flowchart, and algorithm were all discussed on.
2. In order to include all features of the design regarding the different functions of the design, the following modes of operation were agreed on:
a. Mode 1. Start at 0 degrees absolute angle (polar coordinates, minimum -190, maximum 190 degrees.). At each angle, wait for the temperature at the bottom of the meat to rise by X degrees Celsius. Turn sequentially to the following angles: 0, -180, 90, -90, 135, -45, -135, 45, repeat. If, at any point after the first complete rotation, the temperature of one of the four measured sides is Y degrees less than the average of the four, turn to that side until the current average temperature is reached, then continue the sequence where left off. Display status degrees, temperatures, elapsed time at angle and status of heating a too cold side.
b. Mode 2. Like mode 1, but only the first four angles
c. Mode 3. Like mode 1, but with a time limit instead of delta temperature limit at each angle.
d. Mode 4. Turn at a slow constant speed. When the end of the rotation is reached, go quickly back 360 degrees and start over in the same direction as before, at the same constant speed. (Otherwise, one side is grilled slightly more than the other.) The change of direction should be smooth, not abrupt.
e. Mode 5. Like mode 4, but turn in increments of 20 degrees and wait for Z seconds at each angle. When the end is reached, go quickly back 340 degrees and start over in the same direction as before.
f. In all the modes, the indicator for proper cooking of the meat was reaching the temperature at all sides to the target value.
3. In order to provide a user-friendly setup for the consumers for choosing their desired settings, and LCD display with some buttons were considered.
4. Also, to make sure that different consumer cooking tastes and demands were included in the final design, a wide variety of cooking options were carefully reviewed and discussed and finally 5 general cooking modes were agreed on. These options as cited in the above section covered almost every taste and cooking type. Such options like how the meat in the rotisserie was to be rotated were considered to be displayed on an LCD. Considering a large number of different options, an LCD with 6 momentary buttons was selected with 5 buttons for changing the temperature of meat and fire, measuring the charging level of the battery, speed, and direction of the rotation and the remaining one for sending the configuration parameters to the main board. Also, an Atmega32u4 was used that could add 13 ADC pins.
5. Regarding the proper sensor for this design, a PT1000 was selected. This sensor has many advantages like offering an excellent accuracy over a wide temperature range (from -200 to +850 °C). Due to its robust and accurate functions, his sensor is extensively used in food industries.
The main challenge with using this sensor was that despite the fact that the relationship between the temperature and the resistance for this sensor is approximately linear over a small temperature range, for a large temperature range, the non-linearity deviations had to be taken into account; otherwise, the requirement for fine tuning of the temperature could not be met. In order to resolve this problem, a current source was used to read the current value of the sensor.
6. The final design was simulated by Proteus to make sure about its proper function.
7. In order to make the design flexible enough to incorporate last-minute modifications, the design was made using an Arduino micro that had a good number of ADC pins. This provided the designers with the flexibility to finalize the work with all the requirements.
8. Another challenging feature of this project was the complexities of making the firmware. Due to the different options and varieties of the rotisserie’s work like its cooking modes, the rotation pattern of the rotisserie rotation axis, etc. that needed to be included in the design, a complete algorithm was created and then further developed during each design step.
9. The control of the motor’s angular speed was done by a PWM design. The design also was capable of changing the direction of the rotation at any moment.
Results and feedback:
After 4 months of work, the final design was completed. The design met all the requirements set by the client and brought his full satisfaction. The final feedback of the client was “Meee Services worked very systematically on my PCB design and firmware project. The design engineer is experienced in the field and reliable. I will now hire them for my next project.”