PBP projects for R/C models

[Ioannis]

Hi Ken.

I would like to ask, is the steering servos linear in control or just like ON-OFF switch?

I mean can you control the amount of turn, or the angle that the car will turn? Or is it full right, full left and center?

Also I cannot see if you really have speed control over the car. It seems that it accelerates fully in every direction.

Anyway, sure it is very nervous in reactions. I will repeat my self and tell you to have a look at PID control. It is the only way to have smooth control of the speed and steering.

Ioannis

[Kenjones1935]

Yes, the difference between the 1/10 scale TOY cars and MODEL cars is proportional controls and $150. The original idea came from the URL below. In it is a 1/12 scale TOY car (cost about $25). He took out the radio control electronics completely.

http://letsmakerobots.com/node/696

I put my toy car up on blocks and used a large cardboard to simulate the presence of a wall on its right. I could not, even with me in control of the distance, get the car to steer straight ahead. Using my model level car it was easy. My code gives a window of 12 to 24 inches from the right hand wall for which the car should steer straight.

Ken

[Kenjones1935]

I think the model level car is getting close to understandable. Not so the toy. This video shows one under control, not the other.



One more step for the model level - get it more up to speed. This needs a bigger room. I've got that, but it needs cleaning. The toy level needs my understanding of the servo that drives the steering. Presently the car does not easily go straight hugging the wall. It just goes left or right. I will clean up and post my code.

Ken

[Ioannis]

It looks like your sensors are not detecting long distance and that is why it hits the walls.

Can you make a test program and see with RS232 or LCD the distance it actually measures? And then use both sensors as it may interefere each other.

Ioannis

[Kenjones1935]

I took the car to an old gymnasium this morning. I had adjusted the "frontfree" distance from four feet to five feet.
That's the proximity response from the front sonars which triggers the code to turn sharply left.
I left the potentiometer at the speed that was too fast for my garage. In the gym it negotiated the corners fine, but could not hug the wall.

I may need to recalibrate the steering, but more likely I need to restructure the wall hugging code.

Here's a link to the code I am presently running. The only difference between the toy car code and the model car code is the servo and DC motor driving commands. For the model code I use the HPWM PicBasic command. For the toy level I command certain pins to be HIGH or LOW.

http://www.employees.org/~kjones/HPI2_left_SyRen02.htm

Ken

[Kenjones1935]

I made a video today of my model level robocar going about 1/2 speed inside an old deserted gymnasium. It largely works. I am now pretty much at the end of my road. YOUR IDEAS???

1. The kit fits underneath the body skin. It is reasonably robust.
2. The kit costs less than $80. The model car costs ~$200 assuming we do not have to purchase the HPI ESC-15 and we can swap in the SyRen ESC.
3. PICBASIC code is not too difficult for middle school students.
4. A potentiometer controls the speed. No need to go back to the USB port for that adjustment.
5. Pulse Width Modulation is necessary ( and understandable).
6. Each car needs PWM calibration of its steering.
7. The characteristics of sound (sonar) must be understood.
8. This is a good example of 'how things work' in the 21str Century

http://video.yahoo.com/watch/8324343/22230090

Ken

[mackrackit]

Do not forget the cost of PBP.

[Kenjones1935]

Yes, the PBP is not freeware. But from the point of view of a middle school club or group project it is a 'one of'.

I did not anticipate the complexity of upping the speed of this car and only asking it to follow the wall. This has been a good lesson for me.

Ken