Programmable Potentiometer/Resistor For 12V DC Motor

[Scotty Rienschield]

I am looking for help in building this or for someone to contract it out to. What I am looking for is the ability to control output to a small dc motor via a programmable unit. Here is a breakdown of what I am looking for...

Use- Slot Car Drag Racing

Ability- In 1:1 drag racing, there are several controllers available to allow a piston driven engine to take off with limited power and gradually bring the power in so not to lose traction to the drive tires. This limiting could be done through timing, boost control (turbo application), or nitrous moderation. Slot car drag racing is a scale version of this...typically 1:24. We use several types of small DC motors with an input current from the track of 14-16v. We use a trigger type controller to take power from the power supply and send it to the track which powers the car. There are several controllers with resistance capabilities...but even the closest to what I am looking for only allows two power settings....basically a timer that the vehicle leaves under a resisted power and when the timer runs out, it allows a second power level (typically 100%). I am looking for a way to smooth this out with several adjustable levels...or even a time/resistance graph.

Functionability- This module, when powered by the incoming voltage (typically triggered by a microswitch)...would moderate the outgoing power to the track...increasing the voltage at a predetermined rate. The complete time of the car traveling down the track is typically between .700 and 1.800 seconds....so it would need to be programmable down to at least .01...but preferable .001 seconds.

I have been researching it for a while, but I have very limited knowledge of electronics and don't even know where to start. I will start with what I have here...and I am will be ready to answer whatever questions you guys have for me...

 

[Arouse1973]

Hi Scotty, the usual way we would modify the power to a motor in this application is with PWM. It is only one car at a time on the track? Or several? Do you have the spec of the motor, with regards to how much current they draw? I don't quite understand what you mean by modify the time down to 0.1secs?
Thanks
Adam
Welcome to EP BTW

 

[Scotty Rienschield]

Adam,

Thanks for the response...

Each lane is powered/controlled separately....so it would only be controlling one vehicle/motor. There are several different motors....the most powerful hits nearly 300amps, but then drops off after the initial startup. When I say modify the time, I am looking to control the power vs. time. My vision is to control via a graph system where you just plot/connect dots to set up the power output ramp. It would need to be able to be controlled in increments of at least one hundredth of a second (.01)....but preferably down to one thousandth of a second (.001). So maybe the initial output starts at 15% and then @ .075s it raises to 25% and then @ .100s it raises to 30%....and so on.

 

[Arouse1973]

Ok I get it now. So you are looking for a timing increment of 1 ms then. That's not a problem for a PWM circuit. What you are after is an ESC (electronics speed controller) We used to use 1200 Amp versions for our RC 10th scale touring cars.
Adam

 

[Martaine2005]

I have a few of these, porsche, Taurus, Tvr and Ford.
I am happy to see them in their boxes.

 

[Arouse1973]

LOL I can't believe you have a Dewalt one...

 

[Scotty Rienschield]

Adam,

You hit the nail on the head....exactly what I'm looking for. I raced RC cars as well...and yes...an ESC without all the bells and whistles... and no radio frequency control.

 

[Martaine2005]

4

 

[Arouse1973]

Adam,

You hit the nail on the head....exactly what I'm looking for. I raced RC cars as well...and yes...an ESC without all the bells and whistles... and no radio frequency control.

That's it... connect into it with your control gear and away you go. Give me the part number of one of your motors and I'll have a look for you.
Adam

 

[Scotty Rienschield]

Pro Slot- PS4021 would be an example of a motor. There's not much good info on current draws and such though.

Do you know of an already available unit that might do what I need? I've never really worked with one that had the functionality that I'm looking for?

 

[Arouse1973]

The ESC only need a PWM signal and power. So as long as the PWM is set up right then I think it will work. Let me have a look.

 

[Arouse1973]

Maybe something like this? http://www.amazon.com/Hobbypower-Voltage-Brushed-Controller-Off-road/dp/B00DU4A8QE
The 320A will be for a burst. But not sure what you would call a burst. You would have much more options if the motors where brushless.
Adam

 

[Scotty Rienschield]

I can see how this fills part of my need....but how would I program it or tell it what to do? I agree with the brushless aspect....RC has converted almost entirely to it.

 

[Arouse1973]

You would need some kind of PWM interface that you can control from a PC. I think we need to put together a sort of block diagram that people can see on exactly what you want to do. This is not a beginner project. What's your time frame for all of this. This could be a nice little project for us. There will be other great guys on here that will also be up for helping.
Adam

 

[Arouse1973]

Let me have a think about this tomorrow.
Adam

 

[Scotty Rienschield]

I really don't have a specified time frame...or any expectations anyways. I have no experience...so I don't even know what to expect! So...if anyone is willing to help, it will be much appreciated. I could put it to use as soon as it was done...but nothing like it exists and we've made due...so it's not like I need it to perform a task. More of a concept than anything...or at least an improvement on the technology that we currently have.

 

[Scotty Rienschield]

I'm ok with spending some money though....would like to be less than $500 though?

 

[Scotty Rienschield]

For some visual references of things...I've attached a couple images...

One is a picture of a controller (file named Difalco) that we currently use...one of many available, but it gives you an idea of some pieces they use. Another picture of a controller (Stealth) is a power limiting controller using dials. The Difalco allows you to adjust power until full throttle...and once the microswitch is hit at full throttle, it triggers the relay at the end of the wires to basically bypass the controller completely for full power (track power comes in and goes through the relay and right back to the track). The Stealth functions the same as the Difalco, except it allows you to control the power at wide open throttle as well. It also eliminates the wiper and just uses micro switches to trigger everything. It does include a relay at the end of the wire that you can activate with a switch...but then you're really not using the full functionality of the controller. They did this so that you could use this controller for multiple classes/uses. I envision my end result being built on the same frame...but pretty much just being a trigger that activates a microswitch...that sends the start signal to the module controlling everything. The module would not use track power to power itself, I would use batteries for this (hopefully a combo of 9v).

The second is kind of what I envision the computer interface to look like. The horizontal would be time...and vertical would be the power limiting factor (ohms or maybe % of full output). As with this graph, the line would preferably be able to be manipulated at several points...as opposed to just a constant increase in power over time. This would be due to adding power at a slower rate until the vehicle speed reached a certain point and then the rate could be increased at a faster pace. This is because the vehicle is less vulnerable to lose traction at a higher speed....so the higher the speed, the faster the power can be brought in. This is easily seen with almost any regular car...hit the gas hard from a stop and it may chatter or spin the tires...but if you're going 30mph..you would need a substantial amount of power added to spin the tires.

The last picture is a product that I could use to create a much simpler version. It basically allows you to program 5 timers that start from a signal. In theory, I could connect each timer to a relay that is connected to a voltage limiter preset at a certain setting. And have each set to a higher setting (limiting the voltage less). This would probably work for my needs...but the above idea would have a nearly infinite number of settings as opposed to 5....which would also make the transition to each smoother.

 

[hevans1944]

It's way above my pay grade for the moment, but this looks like an ideal candidate for a cell phone app communicating with an Android Uno over a Bluetooth link. The cell phone app would allow you to create a graphical acceleration profile that gets down loaded to the Arduino producing PWM power to the motor. There should be a "START" button on the Arduino box to begin the downloaded profile, and perhaps an "ABORT" button, too, if the profile turned out to be a little too aggressive for a particular setup.

The cell phone/Bluetooth wireless connection isn't absolutely necessary of course, just way-kwel. You could also use a laptop and a serial connection to the Arduino Uno PWM box to download the acceleration profile.

When did slot car racing come back? I remember slot cars from the 1960s, but we didn't have neodymium rare-earth magnets back then. A magnesium chassis was the rage, along with hand-wound armatures and oh-so-soft wheels for maximum traction... The best tracks used braided copper conductors (instead of solid copper strips) inserted in routed grooves flush with the track surface. By the time I finished my Air Force hitch in 1967, slot car tracks had all but vanished from the Dayton OH scene. <sigh>

 

[Scotty Rienschield]

Hevans,

Thanks for your reply. Slot car racing, at least to me, has been pretty big in certain areas for at least the past 10-15 years. There's actually national level races both road coarse and drag racing just South of Dayton near Miamisburg.