Mine is a very simple application where a stepper or DC motor moves in each direction till it hits a switch. When a switch is triggered it will reverse the motor towards the other side. The motor will move a carriage along an aluminum alloy rail at a speed of 2m/minute.

The carriage's total weight is 5kg which includes 4 trolley wheels, 1 drive wheel, a battery, 100g load, its aluminum body, and an allowance of 300g motor weight. The linear movement will have no incline or decline.

If possible, we would like pitstops every 5 meters, that's in between hitting the switches.

We want to use between 5v and 12v power input. Battery operated, low power consumption is an important consideration and so I would really appreciate your guidance on this.

I have 2 main queries that I need help with.

1) based on the above variables, our calculation suggests that either NEMA 17 or DC motor with 0.42N.m is sufficient. Any thoughts?

2) Its one-speed movement, exactly the same load each time and stop do not have to be precisely accurate. If power consumption is an important factor, would you suggest a stepper (with gear) or a brushless DC (with encoder) motor? motor cost is not a major factor.

Thank you so much for your help.

 

Is this for use with a Camera ?

A Stepper-Motor is probably not the best choice, unless precision positioning is required.

Does it have to be silent ?

Does it have to stop at various preset positions ?

Does it need to stop and start smoothly ?, or is abrupt movement OK ?

The mechanical details need to be established before a Motor is chosen.
Cable ?, Threaded-Rod ?
Exact speed range required ?
.
.
.

 

Welcome to AAC.

Is this school work?

 

I will give you the same answer here as in the other forum you posted this question in. Since your speed is a constant speed control is not an issue but keep in mind if using a stepper driver there are software routines which allow speed to be ramped up or down. I would go with a stepper and a gear reduction box. I do it this way so my travel transition is nice and smooth. You already have your data for the force required so that is not an issue. Direction change is not a problem but I would suggest a brief pause on direction change. If this is any sort of commercial or industrial application choose quality parts from a reputable vendor is my suggestion.

Ron

 

1) based on the above variables, our calculation suggests that either NEMA 17 or DC motor with 0.42N.m is sufficient. Any thoughts?
2) Its one-speed movement, exactly the same load each time and stop do not have to be precisely accurate. If power consumption is an important factor, would you suggest a stepper (with gear) or a brushless DC (with encoder) motor? motor cost is not a major factor.

I much prefer DC motor, as it can be ramped up using a simple drive amplifier, and you do not have to constant motor rated current through the whole process., especially if battery life is an issue.
e.g. if stopped at a limit SW, if motor is not turned off, the motor rated current will still occur.
If accuracy is not too precise, then limit switches would work, and an encoder would not be necessary.
If any gearing is used, worm and pinion for e.g. then back feeding will not occur, if thought to be an issue..
BTW, NEMA 17 indicates the size of the motor mounting frame, not the torque rating.

 

Is this for use with a Camera ?

A Stepper-Motor is probably not the best choice, unless precision positioning is required.

Does it have to be silent ?

Does it have to stop at various preset positions ?

Does it need to stop and start smoothly ?, or is abrupt movement OK ?

The mechanical details need to be established before a Motor is chosen.
Cable ?, Threaded-Rod ?
Exact speed range required ?
.
.
.

- Yes, its for a use with camera.
- Precision position not required.
- yes, noise is a factor
- yes stops are approximate e.g., every 5m
- need to stop and start smoothly yes.
- it will run on a rail and it will be a very slow moving motor. Around 30rpm. Very similar to those light mover rails like this https://www.ebay.com.au/itm/195575648381

 

I will give you the same answer here as in the other forum you posted this question in. Since your speed is a constant speed control is not an issue but keep in mind if using a stepper driver there are software routines which allow speed to be ramped up or down. I would go with a stepper and a gear reduction box. I do it this way so my travel transition is nice and smooth. You already have your data for the force required so that is not an issue. Direction change is not a problem but I would suggest a brief pause on direction change. If this is any sort of commercial or industrial application choose quality parts from a reputable vendor is my suggestion.

Ron

Thanks Ron. My major concern now is the battery life.

 

Welcome to AAC.

Is this school work?

Not a school work.

 

I much prefer DC motor, as it can be ramped up using a simple drive amplifier, and you do not have to constant motor rated current through the whole process., especially if battery life is an issue.
e.g. if stopped at a limit SW, if motor is not turned off, the motor rated current will still occur.
If accuracy is not too precise, then limit switches would work, and an encoder would not be necessary.
If any gearing is used, worm and pinion for e.g. then back feeding will not occur, if thought to be an issue..
BTW, NEMA 17 indicates the size of the motor mounting frame, not the torque rating.

Thank you. The battery life is my main concern. In terms of the NEMA 17, the torque we have is 0.42n.m. If a small enough stepper motor is used, and it is completely stopped at every interval, will it make a better choice in terms of battery usage and other features combined?

 

Thank you. The battery life is my main concern. In terms of the NEMA 17, the torque we have is 0.42n.m. If a small enough stepper motor is used, and it is completely stopped at every interval, will it make a better choice in terms of battery usage and other features combined?

Stepper drivers typically power the motor coils even when the motor is not moving- very hard on battery life.

 

You will probably get better help if you describe the actual application and not just the facts you think are relevant. If you knew what information to extract you wouldn’t need help, but you do need help.

The actual application will provide a context and information you might not even realize is included. There is a lot of guessing going on because of the “simplification”.

 

You will probably get better help if you describe the actual application

Thanks for the tip. The rail and carriage setup looks similar to the attached image. Rail mounted camera moves from A to B, mostly around 100 meters in total but the exact distance may very in every installation. It stops every 5 meters to take videos. When it reaches the end, an analog switch touches the end cap and so the device goes to sleep for a predefined interval. Once it wakes up, moves in opposite direction and repeats the same process. The saved stream is periodically sent to an onsite EDGE device for AI processing.

The sleep duration is 1 hour and it will move during the day only so at the max, it will have 6 trips from A to B and then 6 return trips.

The device has a detachable battery and we want to extend the battery life as much possible. Preferably in days if not weeks.

Hope its clearer.

 

I think your design would be greatly simplified by using physical markers on the gantry to indicate where the trolley should stop. That way, you don’t need to concern the on-board electronics with navigation–it just moves until it encounters a stop marker and does it’s thing.

The markers could be something that operates a physical (mechanical or optical) switch, or it could be something that is recognized with an optical sensor, or RFID, which could actually contain instructions (stop here and record for N seconds, stop here and sleep for N seconds, then reverse, etc.) allowing you to make the path flexible.

Using the markers would mean your locomotion mechanism could be brain-dead simple, like a DC gear motor. If you wanted to, you could even have markers (assuming you use bar codes or RFID) that provide acceleration and deceleration commands for the moves between stops. But, if you just crawl, there would be no problem stopping in time anyway.

Also, it appears that you could include some solar energy power scavenging to increase time between charges. If you would like it to be unattended for a longer time, you might be able to adopt the robotic vacuum strategy and have it dock with a charger at (either) end of the gantry.

In any case, I think you should probably simplify your motion design. Steppers and complicated motors are not only more power hungry, they will be heavier and more complex to use.

 

I think your design would be greatly simplified by using physical markers....If you would like it to be unattended for a longer time, you might be able to adopt the robotic vacuum strategy and have it dock with a charger at (either) end of the gantry.
In any case, I think you should probably simplify your motion design. Steppers and complicated motors are not only more power hungry, they will be heavier and more complex to use.

Thank you so much for the detailed reply. I am new to motion design and so these suggestions are greatly helpful.
The idea of using cheap and abundantly available NFC RFID sounds great. With 2-3 different tag codes we could advise to accelerate/decelerate or stop. So, no need for encoders and this could work with any DC motor basically, right? Any suggestion / pointers when choosing a DC motor? I am basically looking to get something that is silent, low maintenance and not so power hungry.

 

Thank you so much for the detailed reply. I am new to motion design and so these suggestions are greatly helpful.
The idea of using cheap and abundantly available NFC RFID sounds great. With 2-3 different tag codes we could advise to accelerate/decelerate or stop. So, no need for encoders and this could work with any DC motor basically, right? Any suggestion / pointers when choosing a DC motor? I am basically looking to get something that is silent, low maintenance and not so power hungry.

Yes, NFC tags were in mind when I described that. Since the motor control would be completely commanded empirically, there would be no need for any tracking internally making things very much simpler.

BUT for safety, you should have a watchdog timer and a physical end-of-travel limit switch. The watchdog would simply be set so that if the trolley ran for longer than some determined number of seconds, it would know there was something wrong (like a bad sensor) and stop, throwing an exception (like a bright flashing LED).

Wireless data is so cheap today, I would be inclined to provide a wireless connection for debugging, diagnostics, and control as well. and controlhere are so many gear motors available cheap. That way you could command the trolley to move to the ends, or stop, or next station—or whatever from the ground.

The physical limit switch could be an opto-interrupter type, but a simply snap action switch (microswitch) would be simpler and not cost any battery at all.

As far as the motor goes, with the plethora of gear motors on the market, I would be inclined to inquire in a robotics-oriented forum expecting the members there to have some knowledge of the best options currently on the market.

What is the reliability requirement? Is this collecting experimental data? Does it merit redundancy to prevent data loss? I can imagine having two motors so if one failed it could still operate. Also, with a wireless link, it could upload the data when it reaches an end-of-travel position, particularly if you provide docking for charging.

 

This is an interesting application, similar to at least one that was presented quite a while back. It seems that the traverse is quite long, because of the stops "every 5 meters", about 16 feet.
With a minimum power consumption goal, a brushless DC motor would be the better choice, and for the end of travel reverse function, a simple mechanically held switch that is operated at the track end, so that no power is consumed holding a relay on.
A brushless motor driver with a ramp-up and ramp down speed function will save a bit by reducing the starting current requirement. For locating the pause locations, the driver can count motor revolutions so that no extra hardware would be needed, or count wheel revolutions using a magnet operated reed switch located on the drive wheel.
So based on that overall concept, a processor type of controller makes sense. The processor does not need to be fast, so it could be a lower power device.
The main limitation on repeatability will be wheel slip, but any accumulated position error will be reset-out at each track-end reversal, so repeatability should not be a problem.
For longer battery charge life, a charging connection could be included at one or more of the stopping points.

 

Yes, NFC tags were in mind....BUT for safety, you should have a watchdog timer and a physical end-of-travel limit switch. The watchdog would simply be set so that if the trolley ran for longer than some determined number of seconds, it would know there was something wrong (like a bad sensor) and stop, throwing an exception (like a bright flashing LED).

Wireless data is so cheap today, I would be inclined to provide a wireless connection for debugging, diagnostics, and control as well. and controlhere are so many gear motors available cheap. That way you could command the trolley to move to the ends, or stop, or next station—or whatever from the ground.

The physical limit switch could be an opto-interrupter type, but a simply snap action switch (microswitch) would be simpler and not cost any battery at all.

As far as the motor goes, with the plethora of gear motors on the market, I would be inclined to inquire in a robotics-oriented forum expecting the members there to have some knowledge of the best options currently on the market.

What is the reliability requirement? Is this collecting experimental data? Does it merit redundancy to prevent data loss? I can imagine having two motors so if one failed it could still operate. Also, with a wireless link, it could upload the data when it reaches an end-of-travel position, particularly if you provide docking for charging.

Thank you so much, some of these points are gold for me. Watchdog and physical switch is surely in mind. Now that we are going with DC motor, we can go with a second motor since they are lighter. We need this to be highly reliable. Its going to be operational in a unattended setup and in remote location and so remotely accessible wireless link might not work. Another reason the seond motor and watchdog will help. thanks. Charging dock is not going to work - no power source.

 

This is an interesting application, similar to at least one that was presented quite a while back. It seems that the traverse is quite long, because of the stops "every 5 meters", about 16 feet.
With a minimum power consumption goal, a brushless DC motor would be the better choice, and for the end of travel reverse function, ...The main limitation on repeatability will be wheel slip, but any accumulated position error will be reset-out at each track-end reversal, so repeatability should not be a problem.
For longer battery charge life, a charging connection could be included at one or more of the stopping points.

Thank you MisterBill2. the brushless DC motor surely seems like a winner. A mechanical switch along with a few NFC RFID for stops are what we are thinking to go with. You are right though, after each track-end any errors will be reset-out. Charging station would have been cool but unfortunately no power source there.

 

Thank you so much, some of these points are gold for me. Watchdog and physical switch is surely in mind. Now that we are going with DC motor, we can go with a second motor since they are lighter. We need this to be highly reliable. Its going to be operational in a unattended setup and in remote location and so remotely accessible wireless link might not work. Another reason the seond motor and watchdog will help. thanks. Charging dock is not going to work - no power source.

The power source could be a much larger battery than you want to carry. The wireless would be for local use when setting up or troubleshooting.

 

That is, you could charge a large battery, like a deep cycle marine battery and use it as a “tank”, charging the on-board batteries multiple times. This could potentially last a very long time.