Hi I'm thinking of a project I would like to do using a ball screw driven carriage
I would want to move an object weighing about 2k along a rail about 900mm long and then returning to the start position and after a delay repeating the loop
It's only in the early stages off planning and wondered the best way to achieve this movement
I could use a simple dc motor and pwm
Or a stepper motor and driver I have a nemia 23 which would attach easily to the ball screw and seems to have enough torque or I also have nema 34 was alternative
What would be my best option as regarding drivers I have an l298n or st m5045 could they be used ?
Don't consider using an L298 with the stepper motors use a specialized stepper driver - perhaps that is what the "m5045" is, but you do not say.
A stepper motor has the advantage of making it easy to a precise distance (number of steps). However if the priority is very smooth movement the DC motor may be the better choice.
Nema23 is the physical size but they come withe differing torque depending on model.
Where's bob when you need him.
Hi yes the st m5045 is a stepper drive I watched a video on you tube by NYC Cnc driving stepper motors using basic accelstepper code but couldn't get it to work properly despite copying the code
If using a dc motor I have a wiper motor with sufficient torque but not sure how best to control it for direction change
You could go with a H-bridge to control direction, or DPDT relay, but you would need a second relay to cut the power.
you don't say what you are doing with the unit.
just moving a slow weight could easily be done with the L298, but as Robin2 said, there are much better options.
if you already have it, by all means use it. if you have not bought it, don't bother.
if you are in the planning stages, the ST-5045 you mentioned is just a cart.... you need to figure out how many horses,...
screws are both very efficient in creating force and horrible inefficient in transferring force.
try a little experiment, take your car to the top of a hill, put it in neutral, then push and calculate the force needed to get to the bottom of the hill.
now, push your car up the hill and see what force is needed.
as you might guess, the results of your efforts will be slightly different.
now, repeat, but stop the car at some exact point going down, then going up. your requirement for brakes will be a bit different as well.
the details needed to do any of these calculations is immense, but if you actually go do it, and within a few minutes you will have a pretty good idea what needs to be done.
if you want to move back and forth in a few seconds, DC motor
if you want to move slowly and stop at various points, selected by your inputs (knob, programs?), then use a stepper.
as was pointed out, steppers come in physical sizes, NEMA-17 is a 1.7cm, 23 = 2.3cm
then they have coils, or stacks of coils. a double stack is two coils, a triple stack is three sets of coil.
there is a lot of engineering before you get to that point. what force is needed to move your carriage, what forces will be acting to stop it, how fast...
the easiest way is to search the CNC forums to find some device that is similar, then ask what they are using and why.
steppers come in physical sizes, NEMA-17 is a 1.7cm, 23 = 2.3cm
Not quite correct - not in cm but in 1/10 of an inch.
Here is the full story:
- NEMA = National Electrical Manufacturers Association.
NEMA chose to label stepper motors (e.g. "NEMA 17") with the size of their faceplate in tenth of inches, which then means:
- "NEMA 17" has a 1.7 inch by 1.7 inch faceplate (= 4.3 cm x 4.3 cm)
- "NEMA 23" has a 2.3 inch by 2.3 inch faceplate (= 5.8 cm x 5.8 cm)
Same applies to the smaller or bigger sizes.
I would like to move a 2kg object about 900mm and back again activated by a motion sensor
If I used the dc motor not sure how I do that and get it to change direction
Thanks you all for the advice I will research further
What is the pitch of the screw (turns per inch)? Is the load to be driven horizontally or vertically? If the pitch is too high, it will back drive and you will need a holding torque to maintain position.
Ball screws generally have very little backlash (one of their main advantages) as well as low friction.
The DC motor changes direction by flipping the poles. Not a big deal.
DC motor changes direction by flipping the poles
Just have a look at "H-Bridges" which can be controlled by an Arduino and will "flip the poles" to reverse the direction.
But as said:
DC motors just turn when they are powered (either left or right) - there is imho no possibility to "hold" them in a certain position -> ok, theoretically with fine adjustments one could try to drive enough current so it just balances the counter force to a stand still - but I assume, that this is for operational environments a no go, because there is a more elegant way:
This is where steppers come into the game (look at CNC machines and especially their z-axis with a pretty heavy load = router plus z-axis construction).
If your load has to be transported up and down you will have to go with a stepper rather than using a DC motor.
Steppers are driven by special stepper drivers.
Let us know what your project is about, especially if the load is being transported horizontally or vertically. Based on your reply we can assist you further.
Ok let me see if I can give a bit more info on my proposed project
I would like to move a small figure weighing about 2kg about 900mm horizontally speed not critical
I have a ball screw with the following
Rm1605 1000mm anti backlash
Dia. Lead ball dia
12mm. 4mm. 3.175
Would like to use
Nema 23
Model. Step angel. Rate cur. Hold torq
St57h5601. 1.8. 2.8. 185oz.in
Rotor inertia
280 g.cm2
Also a Cnc st-m5045 motor driver
Supply voltage 20v to 50v dc
Output current 1a to 4.5a
Pulse input freq up to 300khz
16 selectable resolutions in decimal and binary up to 51,200 steps/rev
I would run this from a 24v 10a dc power supply
So do you think this would be the hardware needed to run my project
Your 4.5A stepper driver should be very capable of driving your 2.8A motor - there is a nice margin between them so the driver won't be overloaded. Make sure to set the max current to match your motor so the smoke does not escape.
You should be able to test things with the simple code in the link I gave you in Reply #1
There is a suggestion for a simple method to measure (roughly) the torque required in the other link I gave you.
If you are moving a heavy load and you want high speed you will almost certainly need to accelerate the motor from standstill. Have a look at the AccelStepper library.
...R
You state the object is moving along a rail. Is it sliding on the rail? On Wheels? How much friction/stiction? Also, Any leadscrew, either ball screw or just a nut, will not move unless the screw is turned. This is a worm screw! You do not need a stepper motor to "hold" the carriage in position. It will stay as long as the screw is not turned.
Paul
paul-kd7hb
yes it would be on rails driven by a worm screw
thank you all for the help I will go away now and experiment using the advice given and see what happens
I will be back with results and any further questions