After putting together the lower platform of the Jetson RACECAR, the next step is to assemble the upper platform. Looky here:
Stiffening the Springs
With the addition of the extra weight from the platforms, computer and sensors, the RACECAR is getting a case of “droopy drawers”. Time to address that issue.
Before continuing the build, we add spacers to the front and rear spring assemblies. The TRAXXAS Rally comes with additional spacers. On the front springs, add two small spacers and a medium spacer. On the rear springs add one large spacer. This has the effect of raising the ride height and stiffening the suspension.
Depending on the total weight being added, it may be prudent to switch out to stiffer springs. Fortunately there are several different spring sets available for the car.
Lower Platform
In the video, the IMU is added to the lower platform using 1/4″ standoffs and 4-40 screws with nylon washers.
Upper Platform
The upper platform has three major components:
- Stereolabs ZED Camera
- Energizer 18000AB Battery
- TP-Link AC1750 Router
The MIT RACECAR uses the router to get a better signal and boost connectivity with the car. This may be optional depending on your circumstances. The Energizer Battery is interesting. The battery is 18000 mAH with three output voltages. The 16-20V outlet drives the Jetson. The 12V outlet drives both the USB hub and the router. There is a 5V USB outlet which is currently not used.
Using two batteries on the vehicle, one for the motor and the other for the sensors and electronics, keeps the sources “clean”. Motors tend to “dirty up” power supplies, and under load can cause voltage drops and spikes. Having two batteries eliminates that issue. There are circuits which can keep the power supply clean of course, but for now the two battery solution seems like a good choice.
There is a mounting hole for the ZED camera on the top platform. The ZED provides stereo vision capabilities to the vehicle.
With the judicious application of 3M Double Lock Fastener, both the battery and the router are mounted on the platform, as shown in the video. Both the battery and the router use the same mounting pattern so that both can be on the vehicle, or the battery alone.
The ZED is mounted using a 1/4″-20 3/8″ screw.
The platform is mounted on 1 3/4″ 3/16″ hex 4-40 F/F standoffs with 4-40 3/8″ screws.
Wiring
Preliminary wiring adds an extension cable for the steering servo to the VESC-X. The USB hub has a cable which may be used on the car, but a shorter 6″ USB 3.0 B Right Angle to A cable is wired up in the video. The cable connects the USB hub to the Jetson USB 3.0 type A jack.
The IMU is then wired to the USB hub using a short mini-USB to A cable.
The next step routes the USB 3.0 cable from the ZED camera through the platform to the USB hub. The ZED has a generous amount of cable, so it needs a little tidying up with zip ties.
As the last step, the power from the Energizer battery is wired. A cable supplied with the battery connects the 16-20V outlet to the Jetson power input. The 12V cable needs to be modified to connect to both the USB hub and the router. The cable then connects the 12V output from the battery to the USB hub and router.
Note: If the router is not being used, then the cable connects directly from the Energizer battery to the USB hub.
In general, cable management is an issue. We’ll have to remember to use caution and plenty of fasteners to keep wires away from moving parts!
Next Steps
At this point, the vehicle hardware is just about complete. The next step is to start installing the software.
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