Atmos 4WD Fixing

Written by Kavindu Ratnayake Photo by Kavindu Ratnayake

During the competition season this past summer the team ran into trouble with the front-left motor, which refused to spin. Unable to diagnose the problem in time it was decided to cut the connection to the two front motors and just use rear-wheel drive. This obviously reduced the performance of the car significantly. Since the Mechatronics group is responsible for fixing the driverless car our highest priority task was set: to get Atmos driving on all four motors again.

The first step was to test both front motors. With the help of some more experienced Revolve members we were able to connect each of the motors to a separate motor controller and inverter. Using these we could check if the motors responded any input from the inverter. The front-right motor spun as expected while the front-left gave no response. Checking the phases on the motor with a multimeter showed a very high resistance between two of the phases. We concluded that there must be a broken connection inside the motor itself and that the only solution was to replace it.

Even though the faulty motor was confirmed there was still a chance for the inverters responsible for the two front motors to be damaged. To check this, we decided to spin the rear motors, which we knew worked, using the front inverters. This was also done on low voltage using a PCAN to send setpoints to each inverter. We consulted relevant alumni throughout the process to ensure that what we were doing was right and to learn as much as possible about the system. All inverters were confirmed to work so we could go ahead with the motor replacement.

A replacement motor was taken from our 2017 car Eld. Both the replacement motor from Eld and the bad motor from Atmos were drained of oil, removed, and stripped of all their attachments. We took pictures as we worked so we could check when assembling everything together again. One of the challenges we encountered was the cooling jacket around the motors which allows the motors to be water-cooled. The jacket on Atmos, being newer than Eld’s, was much slimmer and lighter. The jackets were press fit and sealed with silicone. After consulting alumni, we decided the best way to take out the motor was to 3d print a cylinder to act as a jig and press out the sleeve. To everyone’s relief this worked perfectly, and we were able to continue our work. Once the motor was finally mounted back on Atmos we had to connect it back to everything else. A new cable and connector were spliced on, the oil cooling loop reattached and filled with oil, and the water-cooling loop reconnected. After checking for leaks we connected all four motors to the inverter in preparation for the final test. Sending messages through the PCAN we were able to get all 4 motors to spin simultaneously. Atmos was back on four-wheel drive!