Need POT to go forward till stop then reverse motor automatically coming back 2 start

[adambowersva]

I have a speed controller for my contraption that will do polarity reversal for motor when running forward/reverse. Now I am in stage trying to design the throttle assembly for controlling the speed/direction. Ideally I would like to use a typical thumb throttle like those found on an electric scooter where the motor will run forward while throttle is pushed to it's end, then automatically reverse polarity and run reverse while throttle is returned to original "off" position. Is there anyway to configure this?

If not, the next option is using something like a remote control car throttle or turning wheel like they have on the controllers typically. Can one of these be taken and used somehow to operate on a speed controller in the typical fashion of a potentiometer?

Any help that can be provided would be appreciated. Thanks.

 

[adamey]

Do you need the motor to move to a specific position when you press the "throttle" where the position depends on how much the "throttle" is pressed? And do you need to move the motor back to a specific rest position?

Or do you simply want the motor to run forward continously while the "throttle" is pressed and reverse continually when the "throttle" is off?

 

[adambowersva]

The motor will run continuous till a lever hits a cutoff switch at the end of it's travel. It will then need to reverse till it hits another cutoff switch at return to start position. Motor position isn't important as the switches will kill motor at ends of travel. What is important is being able to control speed of the motor in both directions.

So ideally being able to use a thumb throttle to control forward speed then have it control reverse speed on return to start position.

You see, there are potentiometers out there that are Forward-Off-Reverse and are off at center position. Examples would be those that operate the seesaw style throttle on a mobility scooter. However, my application preferably calls for a throttle that will control forward one direction and reverse returning to start.

Hopefully I have added more clarity to my predicament. Thanks.

 

[adambowersva]

Do you need the motor to move to a specific position when you press the "throttle" where the position depends on how much the "throttle" is pressed? And do you need to move the motor back to a specific rest position?

Thinking about your reply now I should say that it seems your first question for clarification would also work. As the cutoff switches stop the motor at a certain position if you have a way for the throttle to control the exact position that would be great too. The motor and controller being used however are 12v DC motor. No stepper type system is being used here.

 

[adamey]

I think what you want is a servo controller. Do you already have limit switches installed, or can you exchange them for another potentiometer?

I've used these before and they work great. IMO, a bargain at $50 for what you get. They also sell a higher current version.

Pololu - Pololu Jrk 21v3 USB Motor Controller with Feedback

Your "throttle" is the position input and another pot on your motor is the feedback input. There'a a great utility you set up using a USB connection from your PC. You calibrate both pots and can set your neutral (off) position for the input. You can also set things like max motor current and even how fast you want to move in each direction.

For example, on one of my projects the motor was connected to a spring loaded lever so power failure would always return to rest. This meant that more current was needed to move in forward than reverse (going against spring tension vs going with). By adjusting motor current I was able to get my lever to move the same speed in both directions even though the spring was assisting reverse.

 

[adambowersva]

Adamey, you are pure genius!! I have never seen these or even considered such an option of a programmable controller within my realm of experience, but these seem like they may be pretty easy to configure, no? For my application it seems though I would need the bigger one that is twice as much (due to current requirements exceeding 3A of the smaller option) as listed here:

Pololu - Pololu Jrk 12v12 USB Motor Controller with Feedback

Now doesn't this then mean that I won't need the speed controller that I have already ordered? This is the controller I ordered: Critical Velocity - 15 Amp Bidirectional Digital PWM Motor Speed Controller P/N: BIDIR-115D. If not, I will probably return it quickly while I still can. It is cheaper than the one you mentioned, but doesn't seem nearly as versatile.

Other question about the one you recommended...will I be able to have the POT setup to control the speed curve and reverse as I mentioned? And why did you mention a recommended 2nd POT?

In regards to your question about limit switches...no I have not installed/purchased those yet. Also...my project seems to be a similar situation to the one you mentioned in that it will be a spring resisted lever going forward and spring assisted in reverse...exactly the same!! =)

Thanks SO MUCH for your help =)

 

[adamey]

^ I wouldn't say genius. I'm always asking questions for help here - it just happens that I already went through something similar to you.


The controller you linked would be more suitable if you already had a microcontroller for your project and needed something to drive the motor.


The way I used mine is as follows, and sounds very similar to what you're doing:

- My input was a pot from a joystick. It was connected to GND, +5V (from the controller) and the wiper was the input to the Pololu.
- My output was a 12V DC motor connected to a lever through gear reduction. It was spring loaded to return if motor power was cut.
- On my lever I mounted a second pot to measure the position of the lever. My lever moved 90 degrees and I centred the pot so that 45 degrees was exactly midpoint of the pots travel. It was connected to the feedback connector on the Pololu (GND, +5V and the wiper to Feedback).
- When you first configure the Pololu you have to calibrate your input & output pots. You do this by clicking "Learn" on the Input and Feedback tabs of the configuration utility and following the instructions (it involves moving them to their maximum positions and clicking on OK so the Pololu can learn the positions).
- Then it's as simple as powering up your Pololu and testing it. I had mine literally working in under 5 minutes.
- This is a servo system, so the controller is always trying to move the motor (and your lever) so the voltage output of the feedback pot matches the voltage from your input pot. In other words, the output lever will always match the input pot.
- The motor current (and therefore speed) will be proportional to the difference between the input and feedback. In other words, if you quickly press the input "throttle" to maximum, then the motor will get maximum current to try and move your lever (and feedback pot) as quickly as possible. As your lever (and feedback pot) gets close to its target, motor current is reduced until just enough current is provided to hold the motor in the proper position.


A few tips that I learned that weren't 100% obvious in the manual.

- Make sure you know which way your motor turns. The positive side of the motor needs to go to output A of the Pololu for Forward movement.
- Make sure that the voltage output of your feedback pot increases with forward motor movement.
- On the Input tab of the configuration utility, turn off the "Asymmetric" check box. If this is on, the default position for your lever will be in the middle and not at the beginning.
- When calibrating (learning) the feedback pot, make sure the motor is dis-connected. It's in the manual, but it's a very good thing to remember.
- Read the manual. There's a lot to go through, but it's not very complex or hard - but you do need to read everything to make sure you understand how it works (except the section on serial commands, since you won't be using them).

 

[adambowersva]

Absolutely awesome =). I am starting to understand more now =). One remaining puzzle (though seems is more a mechanical puzzle than an electric one) while I await the arrival of my new Pololu controller =)...

I suppose I do have two pots already as I ordered a standard 5k pot with the other controller I got to send back (and the other is the thumb throttle from a scooter I want to use as my input pot). Its a single turn pot...how did you setup the feedback pot on the lever? I noticed from your older posts that it was for controlling a race car throttle. How did you mount this type of pot to turn as the lever is pushed in? Did you put on some sort of extension on the pot to function almost as a cam or what?

Thanks for all the help so far...you have been the only one to respond on this thread and have given me more enlightening insight than I could have expected to get from a whole group of responders.

 

[chergar]

Don't think this is in the right forum but didn't know where else to post. Since my question is similar, perhaps I can get help here. I want to build a simple horizontal tracking system. I presently have a 1/6 h.p.110 v. motor/speed reducer producing 30r.p.m.I,foolishly, thought I could use a threaded rod in the speed reducer to move the array at the speed the sun passes.I proposed to use a drum switch to reverse direction at each end of travel/day.I thought if it ran for 5 or 6 hrs. a day it would prove beneficial,say 10 a.m til 2-3 p.m.however the drum switches have a "center off" position which shuts everything down.As well the motor should come to a complete stop before changing direction [at each end]I am mechanically o.k but electronically challenged. any help would be appreciated.An afterthought,the array would remain in the 2-3p.m position until approx. 5 p.m.and then return to the 10 a.m position. Obviously a timer will also be involved

 

[mbarazeen]

you could better post in a new thread, there are many easy to make solar tracking system using LDRs & op amps. next day when the sun comes in opposite direction it can return to initial position automatically too. search on this forum or on net.

 

[Boncuk]

Hi,

I guess you are talking about an RC speed controller. It requires pulses varying in length from 1 to 2ms, while 1.5ms is the neutral position (motor off).

Here is a cheap circuit which can be used for servo testing as well.

It features a dual output, one logical high and the other one inverted.

Board design is purely single sided and dimensions are 47.95X32.7mm (1.8875X1.2875").

If it fits your needs please PM me your full name and email address. I'll send the Eagle files right away.

Regards

Boncuk