I just bought the A4WD1 autonomous kit (botboarduino).
I’m really new to electronic and the assembly guide doesn’t provide much information.
As I would like to avoid toasting everything when I’ll plug it on… I will ask a couple of questions first.
The sabertooth 2x10 R/C specifies we can connect lipos to it (between 2S and 6S).
But I suppose there is no regulator ? So I have to choose between 2S and 6S according to the motor specs ?
If that’s the case, my motors are GHM-01, so 12VCC.
Which lipo should I use to power the motors ? 3S (11,1V) ? or 4S (14,8V) ?
(Btw, would nimh batteries be a better choice) ?
Can I use a 2S lipo to power the botboarduino + the electronic (one ultrasonic sensor, 3 IR sensors and 2 servos) ? If yes, which capacity would your recommend ? Is 430mah enough ?
I received 4 little components in the A4WD1 autonomous robot kit (botboarduino), looking like resistances, with HX3 0931 written on it. What should I do with that ?
Would you recommend using 3S lipo also for the logic ?
Maybe it is a stupid question, but as the servos and the ultrasonic sensors are all working at 5v, why would 7.4V (regulated to 5V) be a bit low ?
I powered the botboarduino with the 2S lipo and it works fine. However, with the external power, the rx and tx leds are blinking. But when using the USB cable to power the board, they don’t blink.
Well, I switched the jumpers, so I first set the jumper on usb, plug in the usb cable, not blinking.
Then I set the jumper to ext, plug in the lipo, blinking.
In both cases, I set all the other servo jumpers to 5V, in order to use the regulator and not toast the servos and ultrasonic sensor.
Yes, I can upload a different program, and run it via usb without the lipo, or via the lipo without usb connection.
I just saw, that removing Serial.println("…"); in my code, stops the leds from blinking when using the lipo power.
But, with the lipo power, the leds are a bit powered up (not much) while with the usb, they are completely off.
Just to be clear, everything works, but I was just wondering why, with the same program, these leds are blinking with the lipo and not with the usb.
Yes, I understand… encoders would be better, but I have just bought the autonomous kit with 4 motors, it’s a bit sad to throw these four new motors away and buy the back shafted ones.
I used a lipo 3S to power the motors and the rover is working fine, I can avoid collision and autonomously move inside a room.
I have two remaining questions:
When I connect the lipo (via the supplied switch) the motors starts running quite fast for half a second, the robot only moves forward for about 3 centimeters, but I cannot determine the cause of this. Do you have an idea ?
In order to turn, I have to power the two left motors in one direction (forward for example) and the two right motors in the other direction (reverse for example). I just want to check if this is the correct way to turn ? Because with less than 50% of the power, the robot doesn’t turn because the wheels stick to much to the ground.
I find a bit strange that I have to buy other motors in order to add the encoder.
I just bought the autonomous robot which is supposed to be a kit containing everything to start making an autonomous rover and actually with the supplied motor it is not possible to add encoders. I think that an autonomous robot needs to be able to determine precisely it’s own moves, so I find it a really strange choice to include the GHM-01 then.
Replacing the 4 motors + add 4 encoders would be quite expensive.
Would the 3axis compass be a good substitute ? I read a lot of articles how to use it, but none of them really mention how precise the measures will be. The robot will move inside an office, so with plenty of materials which could interfer with the magnetic sensors, the robot it-self contains two batteries, motors, servos…
Can I really use that 3axis compass to determine the position of the robot inside a room and precisely compute the heading (this needs to be precise when the robot has to turn) ?
For the GHM-01 gear motor:
The nominal voltage is 12V, meaning the motor runs most efficiently at 12V. Operating it at higher or lower than 12V means it will be less efficient and lose more energy, primarily in the form of heat.
The 90mA value is when you power the motor at 12V with nothing connected to the output shaft (i.e. no resistance). The 90mA is essentially needed to overcome internal friction.
The 1.5A is what happens when you physically stop the motor from rotating - the motor will be trying its absolute best to turn the shaft and consuming as much current as it can. This will fry the motor very quickly, and it’s best to operate a motor at around 1/4 to 1/5 stall, so in this case under normal circumstances it should draw about 0.3 to 0.4A.
The units “Ah” refers to Amp Hours which is a capacity, most often associated with batteries. If you find an NiMh battery rated for 12V, 2Ah, it can discharge at around 2A for 1 hour. If you find the same battery in LiPo (11.1V is the closest), and 2Ah, LiPo batteries can discharge at a higher current, and can go up to 10 times their capacity, which in this case would be 2x10 = 20A.
It supports up to 18V but higher than that may cause issues. Check the specs of the Sabertooth you received because some can go up to 24V (3.7 x 6 = 22.2V) There is no regulator.
3s (11.1V would be best since 12V is nominal = highest efficiency)
430mA is ok, but a bit low. In general, the batteries powering the motors will run out first, and the power supply to the logic will last a while. 7.4V is a bit low for the logic voltage.
The log should ideally be powered at above 9V. 11.1V is lower than the 12V max, so you should be fine.
There is a minimum value a voltage regulator can accept in order to provide 5V. For example 5V input would not provide any output (0V). In theory the regulator on the BBuino requires as little as ~7V before it provides 5V, but we have found this is not reliable (especially when using NiMh batteries where the voltage drops as it’s used up) and always suggest 9V or higher.
It’s one thing to power the BBuino, it’s another to be able to use it at 7.4V. Can you check that you are still able to send and receive signals when it’s powered only by the 7.4V LiPo? Note that there is a jumper to switch between external power and USB power which may be having an effect.
Are you able to upload code normally via USB without the LiPo connected? If so, the board is fine. Disconnect the USB cable, set the jumper to Ext and connect the LiPo - the code should still be on the board - does it work? You can create a simple program to sweet a servo (it’s under the Examples folder in the Arduino software).
You are indeed correct. We will modify the kit contents so that the motors which are included with the A4WD have back shafts.
A 2+ axis accelerate plus compass would be best, since a compass normally gives only the heading, which an accelerometer can provide a sense of distance. The ideal would be to also add encoders.
A 3 axis compass ideally has an accelerometer built-in where you can read the raw values as well as the compass heading. You need to use integration (twice) to get the distances traveled in the compass direction. Given losses due to friction, the process can only be so precise, and will lose accuracy the farther away from the origin the robot moves. Indoor navigation without use of external references is not easy - a robot like the Neato uses a 2D scanner to map the room.
]It is possible that your robot has a startup sequence where the motors are activated for a short time while a microcontroller is booting for instance and the pins are floating. You could add a pull-up or pull-down resistance to the motor control pins to make sure the pins always have a well defined electrical value. /:m] ]That sounds like the right way to turn for differential steering, If you want to reduce friction, you will need to reduce the distance between the wheels. /:m]
