Is the HB-25 the right tool for my project??
w4fej
Posts: 264
After searching the forums on the use of stepper motors for positioning a lead screw assembly I was surprised to find that several folks said the stepper was not the way to go. Ok, fair enough. The most popular method was a DC motor and some sort of controler used with a Prop.
I am trying to locate the ends of an antenna coil that is driven by a 1/4-28 piece of all thread. I have a (from the motor label) 12vdc, 2 amp motor which is fine for the project. The motor is mounted INSIDE an aluminum tube that leaves no room for limit switches to pass by the motor or coil.
I have a disk I made years ago that has four round magnets mounted flat to the disk like a 4 CD changer would be arranged. The magnets are arranged N/S/N/S. I was using a hall effect sensor back then which seemed to work ok. I am NOT locked into using this disk/magnets for pulse counting however what ever method I use I will have to build a "window" above the motor and below the bottom of the coil. I am open to other methods of pulse/turn counting that are compatible with the Prop or BS2 as I several of both.
Back to motor control, is the HB-25 the way to go for the motor control or is there a better control device out there for use with the Prop? The motor will likely never be run for more than 10-15 seconds at a time. Total travel distance for the antenna coil is approx 18" so to go from end to end takes less than 15 seconds.
If I have to resort to adding a window in the side of the tube to mount/position a turn counter then I can also mount a lower limit micro switch.
I'm totally open to any/all suggestions before I order a controller.
Thanks for reading..
Mike B.
I am trying to locate the ends of an antenna coil that is driven by a 1/4-28 piece of all thread. I have a (from the motor label) 12vdc, 2 amp motor which is fine for the project. The motor is mounted INSIDE an aluminum tube that leaves no room for limit switches to pass by the motor or coil.
I have a disk I made years ago that has four round magnets mounted flat to the disk like a 4 CD changer would be arranged. The magnets are arranged N/S/N/S. I was using a hall effect sensor back then which seemed to work ok. I am NOT locked into using this disk/magnets for pulse counting however what ever method I use I will have to build a "window" above the motor and below the bottom of the coil. I am open to other methods of pulse/turn counting that are compatible with the Prop or BS2 as I several of both.
Back to motor control, is the HB-25 the way to go for the motor control or is there a better control device out there for use with the Prop? The motor will likely never be run for more than 10-15 seconds at a time. Total travel distance for the antenna coil is approx 18" so to go from end to end takes less than 15 seconds.
If I have to resort to adding a window in the side of the tube to mount/position a turn counter then I can also mount a lower limit micro switch.
I'm totally open to any/all suggestions before I order a controller.
Thanks for reading..
Mike B.
Comments
Until the smart guys chime in, I will tell you that I have had very good luck with the Parallax HB-25. It is rated at 25 amps, so your 12 volt, 2 amp requirement is well within its capabilities.
All my HB-25 controlled DC motors have built in optical encoders. The precision I was able to obtain with the encoder-driven HB-25 setup was more than adequate for my tracked robot use.
--Bill
Mike B.
Unfortunately these forums all seem to use at mega chips because they don't realize the prop is actually simpler for this.
I don't know the hb-25. If the stepper is the way to go, and imho it is, then you can drive up to 2A motor with a Pololu A4988. Now be careful with 2A because this is absolute max, so try a motor that is more like 1.5a max. Probably a nema17 or 23 may do your job but I don't know how much torque you will require.
I have 2 pcbs that may help. First is a carrier pcb for the pololu module or you can simply wire the pololu directly to a prop board. I have a pololu pcb equivalent using A4982 or A4984 but I have not assembled one yet. If you use the pololu one get the A4988, not A4983 because it is has short circuit protection too. I also have a prop pcb that may help called the baseboard but there are many prop boards around depending on what you also require. My new website www.clusos.com
I would definately use limit switches of some kind.
I am not sure why you are giving up on stepper motors because they are very accurate, unless you are losing steps due to the steppers having insufficient torque or trying to run the stepper motors too fast. Providing that you are not losing steps, the motors should be extremely accurate.
When a project requires indexing from a stepper motor, most people choose a stepper motor with a step angle of 1.8 degrees(equivalent to 200 steps per revolution) and a 1/4-20 leadscrew. The reason behind this combination is the simplicity of the math to obtain linear resolution. To move one inch there must be twenty revolutions, which equates to 4000 steps of the stepper motor. To move 18 inches, simply multiply 18 * 4000. This math assumes full steps.
I am personally a big fan of the G251 gecko stepper drives which can be found here:
http://www.geckodrive.com/g251x-p-38.html
These are micro-stepping drives, with 10 micro-steps per full step. So to move 18" with a 1/4-20 lead screw, this drive will need to send 18 * 4000 * 10 pulses to the stepper motor. Providing that you know where to stop, all you need is the proper math for positional accuracy.
As for speed, well that is a different issue.... I wrote a stepper driver that will deliver at least 13.34 revs per second using the forementioned gecko drive, actually it will do better, because those are old specs.... But to move 18 inches with the G251, a 1/4-20 leadscrew, and my software, it would take approximately 26 seconds.
In case you are interested, here is a link which discusses my modified software for stepper motors and stepper drives:
http://forums.parallax.com/showthread.php?132373-PulseTheStepPin-revisited-Questions-answers-problems-solutions&p=1010783#post1010783
If you intend to use this software, I would recommend reading the entire thread, which is just six posts, and make sure you understand it.
Bruce
SparkFun sells a couple of stepper motors. One costs $6.95 and the other $14.95. I bet either of these would work well with your project. The driver chip I linked to earlier should be enough to drive either motor. These driver chips can be stacked if you need more current than one chip can handle. It would be good idea to get some flyback diodes to use with the chip.
I know I have some code I wrote to drive a stepper motor with these chips. I'm sure there are plenty of better stepper driver objects than what I wrote but you're welcome to mine as well.
With a stepper you shouldn't need an encoder. A limit switch is probably a good idea though.
Depending on what options you choose, you could be up and running for less than $10 (plus shipping) (although I'd suggest getting more than one driver chip (I usually by 10 at a time so they only cost $2.12 instead of $2.35)).
Wow, I just checked the price of a HB-25. $49.99 ouch. I think the HB-25 is way more than what you need. (I do think the HB-25s are good controllers (I have one), it just way more than what you need for this project (IMO).)
With the stepper, you could get the driver and the motor for a lot less than a HB-25. You'd still need a motor for the HB-25 to control if you go that route.
Anyway, good luck on your project.
Duane
Rather than going with a controller, consider that with a stepper motor, one (probably bottom) limit switch could be used also as the index point and then knowing the math for your stepper solution could give highly accurate and repeatable positioning information for the full travel of the rod without the additional cost of a full controller component. The downside of the stepper and index detect is that the system must remember where the last position was when power down occurred otherwise you will need to find index at each startup; not a bad thing, just adds startup delay. If the position could be at all altered, then the index search would become mandatory.
You could also use a potentiometer and if needed gearing to get the absolute position at any time without indexing etc. Using some the A/D techniques already published here, you could read the pot value and convert to position for a driver object again without adding a controller device.
The industrial strength solutions of the systems I maintain, the major axes use both a position pot along with quadrature encoders w/ index and stored digital position values to control position. The quad outputs are used for PID speed/directional/position functions, and are monitored for range of variance between the pot value and the stored/derived digital value. Oh, the motors are large DC motors w/ electromagnetic brakes on them.
These could probably be done with a couple prop cores and save the cost of an external controller device. While the motor you spec'd is 12V@2A, I would guess that 2A is a max current you would only see in the event something bound up, so you could probably drive it with something short of hexfets or lower power darlingtons.
So short answer may be that the prop itself is the more appropriate device to control the positioner.
Frank
First requirement is the round body. Second requirement is the wires must leave the rear of the body opposite the shaft end. Looking at the pictures of most of the steppers it appears that the square mounting flange could be remove leaving a round body stepper. If the flange doesn't do something stupid like retaining the bearing or something that would eliminate one issue. I'll machine a mounting method to mount the stepper inside the tube.
I didn't get a lot of time today to look all across the web for info but I can't seem to find dimension data for the body diameter for the round steppers. I'll keep looking.
Oh yea, did I mention that whatever type motor/stepper I use will be INSIDE the active antenna RF field of up to 100 watts?? The tube itself is the main part of the antenna. At the moment I am using (literaly) a cordless screwdriver motor (3.3VDC with it's own gearbox) on 12 VDC and it works great for running the coil up and down so the torque requirement is fairly low.
So the three remaining questions are: Can the square mounting flange be remove from a round stepper? Can you tell me the round body diameter of the stepper?? Do the wires leave the stepper from the rear or the side of the body..
I haven't yet ordered the HB-25 but was just about to but I will wait until I see if there is a stepper that will fill the bill at a price I can afford.
Thanks for reading.. Mike B.
Mike, in my honest opinion, it sounds to me like you need to reevaluate your initial design, but then again I don't know the purpose of your design, besides moving some type of coil.
Bruce
Ok, I'm sorry. The project is a mobile communications antenna that is motor tuned from 3.0 Mhz to 30 Mhz. The antenna consists of a (usually) 2" diameter aluminum tube about 36" long. Inside the tube is a coil form about 24" long of which approx 18" is coil. The motor drives the coil into or our of the tube. At the very top of the tube there is a contact spring to couples the exposed part of the coil to the tube. The bottom end of the coil inside the tube simply ends, no connection to anything. It is effectively not there. The top of the coil has a standard 60" stainless steel whip mounted to the top end of the coil. By varying the length of the coil exposed I can operate on ANY frequency between 3.0 and 30. Mhz.
The basic design is called a "screwdriver antenna" because it made use of a Black and Decker model 2105 cordless screwdriver motor to raise/lower the coil/whip. I have built three of these guys making incremental improvements each version. The next one I want to add "smarts" to it to do several things such as travel limits, memory locations for frequently used frequencies, a display to show which mem location is used etc. I'll be using a Prop of course.
Now having said all that, I am determined to use a stepper. I thought all day how I could use a size 23 stepper and have sorted that out in my mind. I'll make the mechanical adjustments as necessary.
I have been watching your posts for quite a while and I am sure you have the knowledge I lack. I just got through scanning through Ebay and there are 96 pages of stepper deals. Looks like I can have my pick of size 23 steppers for next to nothing (< $50 easy). Question: There are 4, 6 and 8 wire steppers. What configuration would be a likely candidate for driving my coil?? The installation will be in a car with a 12VDC system. A few words of wisdom from you would be great to get me pointed in the right direction.. Interface to the Propeller??
Thanks Bruce...
Mike B.
But perhaps your step is not so critical and the screwdriver motor might well be suitable and cheaper. Then you would require an hb-25 or cheaper equiv - less power req. You would of course need some feedback method such as a magnet on the shaft and detector - hall effect or reed sw to operate each revolution. Do have a think about this. The prop will work easily with any of these designs with plenty to spare for other things if you desire.
Certainly the stepped is easiest.
Sorry for typos - on android.
I am not certain that I am worthy, but I appreciate your faith in me. The automotive environment, puts a whole new spin on things. That requirement boots that gecko drive out the window, because they require a minimum of 15 volts. In my opinion, it is almost always a 50/50 decision (driver/motor), and when you consider your driver, you must always consider your power supply. In your particular situation, I believe I would start from the battery and work from there. I have seen numerous articles pertaining to special precautions for automotive applications, and I suggest you research this subject well. In most instances, stepper motors run best from an unregulated power supply, however due to the automotive environment, if I were trying to achieve linear motion from a Propeller controlled stepper motor, my first objective "I think" would be a good clean regulated 9VDC power source to power both the stepper and the Propeller.
To try and eliminate all possible headaches, here is what I would strive for:
Clusso99s suggestion looks good to me... Try this link..
http://www.pololu.com/catalog/product/1183
4, 6, and 8 wire motors can be used with this driver, but keep in mind 2A max. You must pay attention to the coil ratings and whether they are unipolar or bipolar ratings.
Bruce
@Bruce, @Cluso99.
Now were talking!! I have to digest all that has transpired here and then spend some time scanning (again) all the steppers on Ebay for the best deal. I need to do a bit of study before I can even comment on your replies!! Thanks guys and I'm off to "school"..
Mike B.
Instead of searching eBay... Do a search on electronic surplus and steppers. I am sure you will find several motors to chose from. Stay away from 5 wire motors.