RPLidar Connection
subodh-malgonde opened this issue · 7 comments
Hi,
I am using RPLidar A1. Your tutorial recommends using a separate power supply for the motor. The motor supply has 3 pins - GND, VMOTO and MOTOCTL. VMOTO is DC voltage between 5-10 V. MOTOCTL is the PWM control signal for the motor. Here is a screenshot from the datasheet.
The PWM signal is generated by the circuit board provided by Slamtec (manufacturer of RPLidar).
However I noticed from your tutorial that you are using only 2 pins (RX/TX) from the board. See this:
Your block diagram also suggests 2 pins.
Initially I thought that if I don't connect the MOTOCTL pin then maybe the motor will run at its default speed. However when I tried this the motor did not start. How are you generating the MOTOCTL PWM?
About the connection of lidar, the order of pins defines as the first figure you post above:
GND: 5V BEC (-)
TX: to FTDI (USB)
RX: to FTDI (USB)
V5: 5V BEC (+)
GND: Dc2Dc (-)
DTR: Dc2Dc (+)
V5: Dc2Dc (+)
In this case, the motor speed is actually controlled by Dc2Dc voltage instead of pwm
DTR and V5 are in the same voltage means that DTR is in 100% duty cycle pwm, which is equal to max V5 voltage. So, you can change the voltage of V5 to modify the motor speed!
Thank you so much @jim1993! 👍 It is clear now. If I want to vary the duty cycle then I can use a potentiometer to reduce the voltage.
One last question about the lidar connection - why did you choose to use a BEC for the lidar's motor? The data sheet says the motor can accept 5 - 10 V, so if you have a 7.4V LiPo battery then you don't need to use a BEC. Am I right?
Hi
As you said, you can connect battery to motor pins.
The reason for using dc2dc module is that we could modify the rotation speed of lidar (Hz) by changing the input voltage.
The frequency is controlled by DTR voltage, right? If DTR and V5 are same then the frequency will be maximum. What am I missing?
Yes, If DTR and V5 are same then the frequency will be maximum.
However, the max freq depends on V5 voltage.
If the input volt is 5V, then max freq is around 5Hz.
For higher freq, it needs higher input voltage (max tolerance is 9V)
Hi @haochihlin , thank you so much for your team's hard work! I would like to reach out that is there any special reason you team also power the core separately (from the USB)? What's the trade off if use the FTDI to power the core (instead of separate power source)?