PBP projects for R/C models

[Kenjones1935]

scalerobotics,

1/10 scale TOY level cars cost about $50. 1/10 scale MODEL level cars start at $200. The TOYs are plastic toys. The MODELs are miniature automobiles.

The TOY cars have only [full on / full off] steering and wheel power controls. Their steering servo has two inputs. Three of the four possible states are used:
[A=7v, B=gnd] ==> steer left
[A=gnd, B=7v] ==> steer right
[A=gnd, B=gnd} ==> steer straight (spring loaded)

The corresponding is true for Forward, Reverse, Brake (due to back EMF) for their DC drive motor.

The TOYs have no differential gears, no drive gears at all, no toe in, no caster, no spring suspension, no dampening and plastic tires. They are inexpensive, fast, lots of fun and colorful. They do a great racing skid turn - just turn the wheel and put the motor in brake state. They are large enough to easily accommodate my solderless PIC kit.

The 1/12 TOYs are considerably slower than the 1/10 size. I have succeeded in making one run smoothly around the room hugging the wall. A bit boring.....

I'm off to the old gym to test my MODEL level with velocity and warning distances now all proportional to the position on one POT. Hopefully now all I need to do is find the correct velocity proportionizing formula for each of the SONAR warning distances which are:
frontclear
frontdanger
stopreversing
desiredtrack
outertrack

Ken

[cncmachineguy]

heres my 2 cents. I think I read somewhere in this thread you are driving the steering/drives with actual relays. First thing to do I think is trade them in for H-bridges. Then you will be able to get much higher switching speeds.

next, see if you can get the steering to become semi proportional or at least slower by pulsing the control. I am guessing it is a solinoid and not a motor for the steering. These take time to move fully, so if you can release the signal before the wheels have turned all the way, it will become at least stepped. the springs will smooth out the signals to make it appear proportional.

Now I am sure you can do the same with the drive. Once you have H-bridges in there, you can PWM it

[Kenjones1935]

cmcmachineguy,

You are correct. My TOYs use DPDT relays (6msec contact. 4msec release - so they say) driven by SN7407's I have been trying to avoid more electronics. I had hoped to have middle school students build the cars using solderless protoboards and to keep the cost down.... I may need to teach-the-teachers first. They did not major in Science, Technology, Engineering or Math in Ed School. Hmmmm.... In Massachusetts that means hooking up with a local college to give a course which teachers take for "professional development points".

I did find that the TOY steering servos are slow to return to zero. A 50milsec kick to the opposite end gets them started. If I could figure a way to control the kick steer, that would be ideal. It is so spectacular.

I am having a difficult time PIC controlling the MODEL car at cruising speed. This is no where near how fast I can make the car go around the track using the R/C, my eyesight and my coordination.

I took it to the gym today with proportional SONAR thresholds implemented. BIG IMPROVEMENT but still it occasionally hit the wall. Don't know why yet......

Thanks again for the interest and support.
Ken

[cncmachineguy]

Any way you can measure the current for the steering? Maybe it isn't real high and you can use 1 of the DIP H-bridge-on-a-chip. The stall current is what we are after here. Then you would still be able to easily proto board it. Leave the relay on the drive motors.

I suspect if you can get the sterring under control, the drive will become less of a problem

[Kenjones1935]

Today in the mail came two toy store Xmas catalogs. Both feature toy level R/C vehicles. All the more reason my autonomous car for introduction to STEM is a good idea. It may be that we need to teach-the-teachers first.

On the subject of cost. In Fitchburg well over 50% of our public school students come from families that fall below the poverty line. In Massachusetts that means they are eligible for free or reduced price school lunches. If we were to use my cars to teach STEM to middle school kids, it would be nice if they could keep what they build. (Maybe in the context of an after-school program.) If we use my cars to guide teachers toward this corner of STEM through a college supported Professional Development course, again it would be nice if the students could keep what they build.

Here's the question. What games can $50 1/10 scale TOY level cars play given the limitations of bang-bang controls and a 16F887 PIC. As a goal keep the total cost less than $100.

Ken

[Kenjones1935]

The point of my project is communicating "how things work" to pre-teens.

Examples of today's difficulties: My Mom's natural gas powered oven was obvious. Ever try to explain a micro-wave? Souping up a car in my day included high lift cams, carborator changes, tuned straight through pipes. Today the first thing you do to hop up a car is change a computer.

The dashboard on my 2004 GM car told me: "TIRE Pressure LR 23psi LOW". It also said, "TIRE Pressure RR 28psi OKAY". I pumped up my left rear tire. Then the car told me,"TIRE Pressure LR 23psi LOW" and "TIRE Pressure RR 33psi OKAY". WHAT??

The garage mechanic told me each tire valve contains a pressure gauge and enough of a computer to maintain a connection to the car's internal wireless network. A previous owner of my car had rotated the tires. The mechanic also told me that my car, depending of accessories, carries some twenty computers.

It seems to me that the first question in the mind of a future STEM professional is, "How does this thing work?"

Ken

[Kenjones1935]

Today at the gym I got two speed levels to negotiate the wall racing. I have divided my POT's full motion into six steps, 0 - 5. 0 is slowest. 5 is fastest.

Today speed 0 and 2 worked fine. Speed 5 crashed a bit. This evening I increased the proportionality multipliers relating POT position to distance thresholds.

If I can get this car up to speed, imagine racing with more than one on the track.

Ken