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Topic: total newb, theoretically simple question about synchronizing motor to input (Read 1 time) previous topic - next topic

psychoboy

Looking at pots more closely, is there a compare function in Arduino?

i run 5 volts to both pots so that resistance is decreased as the pot is turned clockwise. when the wheel is turned clockwise, pot A (at the wheel) is a higher voltage than pot B (at the rack) the logic powers the motor at the rack clockwise, to seek balance between the pots. when pot A is turned back to center (counter clockwise), pot A is lower voltage than pot B and the logic turns the motor CCW to seek balance.

basically:
if Va>Vb, then 1=gnd 2=12volt
if Va<Vb, then 1=12volt 2=gnd

am i anywhere near the right track?
"Racing is an investment in life. You trade money for awesome."

0AlphaOmega

What you describe is effectively a servo.

When you drive, you don't know the position of the rack (some cars have mechanical or electronic systems for adjusting the applied movement depending upon speed and are not 1:1), you turn the wheel to achieve the required radius, as I said, you are part of the feedback system, all you are doing is turning the wheel remotely.

If an RC car travelling at ridiculously high scale speeds is able to cope using an RC servo (using a single turn pot), why can't you just scale it up?

Turning the wheel 15deg on a RC car or a real one, only really differers in the scale of power required.


For whom does the clock pulse? It pulses for you!

psychoboy


What you describe is effectively a servo.


ok...i'm following so far. the servo has a built in pot and it's mimicking the steering wheel pot on the on the controller.

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When you drive, you don't know the position of the rack (some cars have mechanical or electronic systems for adjusting the applied movement depending upon speed and are not 1:1), you turn the wheel to achieve the required radius, as I said, you are part of the feedback system, all you are doing is turning the wheel remotely.


I do need to be able to reference "center" visually. in this gear box, there is no assist, no mechanical trickery beyond gear ratios. when not in motion, i need to know that straight per the wheel is straight per the box.

Quote
If an RC car travelling at ridiculously high scale speeds is able to cope using an RC servo (using a single turn pot), why can't you just scale it up?


i didn't think the resolution on a pot would be fine enough to handle the reduction of 1080 degrees of steering wheel to 270 degrees of pot....

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Turning the wheel 15deg on a RC car or a real one, only really differers in the scale of power required.


that's where i think my problem lies. I'm not turning either end 15 degrees.

1080 compressed to 270 is 4 degrees in real life = 1 degree virtually. at the other end, that 1 degree scales up to a 4-degrees-are-still-accurate window. i guess, if i find a precision enough 3/4 turn pot, i can get the compressed steps into a quarter of a degree (or less) narrowing the output window to 1 single degree.

just got off the phone with a guy from TR Electronics who was saying their "low resolution" magnetic based encoders are something like 4000 steps per revolution. since a normal pot is theoretically more analog than that, then a 3/4 pot might be more than enough for my purposes, despite what my brain wants to believe.
"Racing is an investment in life. You trade money for awesome."

kf2qd

The whole thing could be done with potentiometers. Multiturn pots at each end. What you would be making is just a bigger version of something similar to a standard hobby servo. Basically - at the steering wheel end you would be "creating" a refernce voltage that you would then compare to the voltage present at the gearbox end. and then itf the voltage is higher or lowere you use that to decide the direction and speed to turn the motor on the gearbox. The difference between the 2 is referred to as the "error voltage" This can be done with linear circuits or Analog to Digital circuits.

Using a couple of potentiometers is probably going to be much simpler than using encoders, as absolute encoders would be needed and they get expensive. A good multiturn pot would give good, repeatable feed back.

michinyon

They have done this a bunch of times on mythbusters,  so it can't be too hard.   The video is probably
on youtube.


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