Installing the SPEEDBOX
The installation instructions in this section apply to the standard SPEEDBOX, and the SPEEDBOX with the RTK and/or the internal IMU option. For the SPEEDBOX-INS please refer to the separate installation instructions in this section.
The following checklist is designed to be a quick reference for connecting the system in day-to-day usage. It is recommended that the more detailed explanations of each step are read in their entirety before initially installing the unit.
- Ensure the power is disconnected.
- Secure the unit safely in the vehicle, taking careful note of the mounting orientation.
- Connect the supplied antenna to “RF 1” on the rear of the SPEEDBOX. For the RTK option, connect the rear antenna to “RF 1” and the front antenna to “RF 2”.
- Mount the antenna(s) on the vehicle roof – do not crush the cable in the doors or windows.
- Connect the power to a fused 9 – 30V DC supply, e.g. a “cigarette-lighter” type plug, or other fused power supply.
Mounting the SPEEDBOX Base Unit
In order to give accurate speed and acceleration readings, the SPEEDBOX base unit should be mounted so that it is flat, level, in the correct orientation, protected from vibration, as close as possible horizontally to the antenna, and restrained from moving relative to the vehicle. These requirements are discussed further below.
Correct orientation of the unit is essential. The unit must be mounted with the direction of travel as shown by the arrows on the top of the unit. When mounted correctly the longitudinal acceleration will read positive whilst accelerating and negative whilst braking.
The unit should be mounted as flat and level as possible. The combined speed calculation will compensate for a mounting angle of up to 20° from level, but accuracy is slightly reduced, so for best accuracy mount as level as possible. Neither the raw 20Hz GPS position and speed outputs nor the angular measurements from the RTK option are sensitive to the mounting orientation or level.
The base unit should be mounted as close as possible to the GPS antenna in the horizontal plane, i.e. the best mounting location would be vertically below the GPS antenna (the rear antenna on the RTK system). This ensures that the accelerometers and the GPS antenna “see” the same velocity. In practice, it is not necessary to conform to this requirement if performing low-dynamic testing, or straight line testing. This constraint does however become important if using the combined speed output whilst performing hard cornering, particularly at low speeds.
The base unit should also be shielded from vibration as far as is possible. “Normal” levels of vibration are tolerated with no problem, but particularly harsh vibration may degrade the operation of the GPS receiver, resulting in either reduced accuracy or loss-of-lock.
The unit can be securely restrained in the required position, either by bolting it in place through the four 4mm diameter holes that are pre-drilled in the unit, or by using a secure locking tape such as “Scotch-Lock”.
Note that for the SPEEDBOX-INS, the inertial sensor is within the rooftop sensor assembly on the vehicle roof, and hence the only base unit mounting constraint that need be followed is the avoidance of vibration; the orientation of the INS base unit is not important.
Mounting and Connecting the GPS Antenna
The SPEEDBOX requires a 3.3V active antenna (supplied) which must be mounted in a position giving a good view of the sky. On top of the vehicle is recommended. Care should be taken not to crush the antenna lead with the vehicle window or door closure. In view of the importance of good GPS reception to the measurement accuracy we have provided detailed guidance for antenna mounting on the knowledgebase here; please take the time to read and follow this advice.
On the SPEEDBOX and the single antenna SPEEDBOX-INS the antenna must be connected to “RF 1” on the rear of the base unit. For the RTK option and the dual antenna SPEEDBOX-INS, the rear antenna is connected to “RF1” and the front antenna is connected to “RF 2”. For the SPEEDBOX-INS please also refer to the additional antenna mounting instructions here (dual antenna) or here (single antenna).
Mounting the GPS Antenna – RTK Option
The magnetic mounting antenna strip is a flexible magnetic strip. It contains two antennas that are mounted in the correct orientation and at a known distance from each other.
- The baseline of the antenna strip is 80cm, so the SPEEDBOX-RTK must be configured to use this baseline using the configuration software supplied. If the unit is not configured to this baseline, it will be unable to obtain a lock (this configuration is the default setting for new units when they are supplied with the antenna strip).
- The antenna strip must be mounted in the correct orientation, as shown on the strip. The wires from the two antennas are labelled “RF 1” and “RF 2”, and should be attached to the corresponding connections on the SPEEDBOX base unit.
- Treat the cables with care. If they are damaged, then it is likely that the whole assembly will have to be replaced.
Figure 1. Mounting arrangement for the magnetic antenna strip (RTK option only)
Using two separate GPS antennas for RTK measurements
In some circumstances it may be impossible to use the magnetic strip - if for an example an obstruction exists between the front and rear antenna locations; if the available baseline is too short; if a longer baseline than 80cm is required; or if the use of antennas that are different to those on the strip is desired. In these circumstances, two separate antennas are used to provide the GPS signal to the RTK unit. As long as they are set up correctly, the results will be just as good as when using the magnetic strip. If, however, they are set up incorrectly, then the RTK solution will fail.
It is vitally important that both of the antennas used are of the same type. Using two different types of antenna may cause the RTK solution to fail.
Figure 2. Mounting arrangement for 2 separate antennas (RTK option only)
The general arrangement for mounting two antennas for the RTK unit is shown in Figure 2 above. Both antennas should be mounted on the roof of the vehicle, on the vehicle centreline. The distance between them must be measured, and must be the same as the configured baseline length (this can be changed using the configuration software to match the measured distance if required). The rear antenna is the “base” antenna, and must be connected to “RF 1” on the unit. The forward antenna is the “moving” antenna, and must be connected to “RF 2” on the unit. If the antennas are connected the wrong way around, the unit will not reliably obtain an RTK solution when the vehicle is moving. Both antennas should be mounted in the same orientation; i.e. the cable should emerge from the same side of both antennas to minimise the effect of antenna “phase centre”. It is also absolutely essential that the antennas are of the same type, model and manufacturer.
The SPEEDBOX requires a stable DC power supply, which must be in the range 9 – 30V. This should be connected to the cable loom assembly that is supplied with the SPEEDBOX via a fused connection to the vehicle. A 1A fast blow type fuse is recommended. Once connected to the power supply, the SPEEDBOX will automatically power up and commence its initialisation routine. The current consumption of the SPEEDBOX ranges from approximately 230mA @ 12V for the standard SPEEDBOX to 400mA @ 12V for the SPEEDBOX-INS. More current may be drawn during startup.
Unreliable power supplies are a common source of problems. In the event of any problems, please check the reliability of the power source or try an alternative supply in the first instance. The SPEEDBOX may also be powered from an external battery pack. If you require a battery pack, Race Technology keeps a wide selection in stock - please contact us with your requirements. Because of the current supply requirements, only rechargeable batteries should be used. Disposable cells are not suitable.