Suggestion for servo motor --> big delta robot
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@arnix said in Suggestion for servo motor --> big delta robot:
Sorry for late reply.
To better understand my situation, am sending latest videos. One is with slower and second is on top speed.
Its without up/down movement, just positioning and extruder should position itself on X0 Y0 ( at higher speed it misses cca 10 cm ).1.) https://ufile.io/u2cim ( just click, free slow download / open or save ).
2.) https://ufile.io/1t63o@691175002 and @jrjones88
I think that the problem is in the gearing and lack of encoder. The material that am using at the moment aluminum but pipe wall is 2mm and pipe diameter is 2 centimeters so there should not be any problems, IMHO. As you guys point it out, 10:1 gearbox that am using could be the main problem because it has backlash of 3 degrees which is a lot, at no load. This is the stepper motor that am using :
https://www.omc-stepperonline.com/spur-gearbox/nema-23-stepper-motor-bipolar-l76mm-w-gear-raio-101-spur-gearbox-23hs30-2804s-sg10.htmlHigh ratio belt reducer - DIY :
- i can do that, can you guys suggest some optimal ratio and motor ?
- what kind of setup would you suggest ( power supply, controller, etc. ) that can be controlled by duet ?
Yes your backlash is the issue right now. For the optimal ration and motor, that is a compromise between speed and holding power. Since you have a 1.89 Nm geared to 10:1 right now and it is too slow (you said cycle time is 1.5 seconds, desired is 1 second), your gearing needs to be a smaller ratio, say 8:1 or 5:1.
A belt reduction is a good way to reduce backlash, but depends on how much room you have. If you goto a 5:1 ratio, you might need a new motor as well, since your output torque is reduced by half on your current motor.
I don't know what your budget is (is this hobby or work/school?). If it isn't hobby I would look at Oriental Motors, they have good motors (all kinds) and drives (that accept pulsed input). But you are looking at around $500-1000 per motor/drive combination.
For example, this motor is has 0.05° backlash. https://catalog.orientalmotor.com/item/az-series-absolute-encoder-stepper-motors/az-series-85-mm-absolute-encoder-stepper-motors-dc/azm98ac-hp15And once you reduce your backlash, I would still look at stiffening your frame (cross braces are easy to add in your case). Take a look here: https://youtu.be/p1Lrz0gPvOA
The frame is very beefy compared to the robot. This video also has some good views on the arms (very similar to the current Delta printers, but then again, delta pick and place robots have been around longer than delta 3d printers) -
The cl steppers recommended by jrjones88 would be suitable for this application, but if they are out of your price range you can try to 3d print a belt reducer.
Use a metal pinion with <=18 teeth along with a massive 3d printed pulley in the 140-180 tooth range. Minimize belt stretch by keeping the unsupported belt length as short as possible using rollers on the back of the belt: https://i.imgur.com/nz2bYp5.jpg
I think steppers can probably work for this application, although you could try https://www.teknic.com/products/clearpath-brushless-dc-servo-motors/clearpath-sd/sdsk-models/ maybe.
Also make sure you are correctly setting acceleration for the motors, it looks a little high on the videos you posted.
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- am waiting for latest simulation to complete and i guess it will be ready in 2 weeks.
- there are bunch of solutions but it looks that in the end i will need to choose servomotor ( look at post under this line )
@jrjones88 and @691175002
- i have some budget for this project but $1000 per motor is way to high.
cross braces are easy to add in your case - i was thinking to add some stabilization in the center of the robot but till now i didn't find any solution
- on the other side, this should be then also added into calculation, regarding motor power
- do you have some suggestion on this ?
Belt reducer
I can do this belt pulley system by myself but i was wondering if something like this can solve the problem:
http://www.harmonicdrive.net/products/servo-mount-gearheads/harmonic-planetary/hpgp-planetary-gearbox
There are also option with zero backlash. Unfortunately i can not find any price range..Motor / drive suggestion
- According to application, and if we go with servomotor + gear system... what motor power are we talking about ? 200W or more ? At the time clearpath servo with gearbox could be optimal solution and (i guess ) under $300 per motor/drive.
Arnix
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Harmonic reducers are perfect for this application but cost 4-5 figures an axis. Even second hand reducers off ebay cost $500-1,000 per axis.
To correctly size your servos you should determine the torque and speed that is required, then select the cheapest model that can meet those specifications.
You would basically start with arm length and estimated load then calculate that as a torque back through the gearbox to the motor.
You could try putting this motor into this calculator with 5:1 belt reduction and see what happens. I'm not familiar with the kinematics you are using, but I assume that if one arm can support 70-100% of the expected load then a robot with three arms will do fine.
I recommend picking low speed servos with high torque so that you can get away with the simplest gearbox possible. Faster servos have much higher power density but might require an accurate 10:1 or 20:1 gearbox which is much harder to build or acquire.
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@arnix, if you choose the gearbox ratio carefully then you won't need much power at all. AFAIR you currently use Nema 23 motors driven directly by the Duet. I assume you are using 24V power. If you are running them at 2.4A peak current, then the maximum you can possibly get from them is about 60W each. That's probably more than sufficient; but you should nevertheless work out the torque and speed that you need.
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@dc42
You are correct. At the time, am using 24V/10A power supply from Meanwell (btw. it's quality product).
Current is set to 2.1A.Torque and speed is the main thing in this application, so i have to put this in first place.
Our simulation is 90% done and at the moment, it looks like we will need at least 10 - 14Nm torque to reach this speeds and stability. Am looking at present gearbox that we use... So, if the motor has 1.9Nm holding torque + 10:1 ratio, this should give 19Nm. That should be enough but it looks like this gearbox has max permissible torque of 5Nm so i guess that this should not be good, specially for longer work.@691175002
** I recommend picking low speed servos with high torque...**
According to simulation we need 0,16 / revolutions per second to gain desired working speed.I will reply in more details tomorrow.
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Can you explain in more detail exactly what issues you have when you try to run the present motor/gearbox combination at high speed?
The backlash may not be an issue at low speeds, because the weight of the arms will take it up. But at high speeds, it may be a problem when the arms are being driven down faster than gravity pulls them.
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I will send video... Shortly, after some work , extruder looses positions for few cm and sometimes, it just drops down (specially at high speed ).. I will record 5 minutes video where you can clearly see what's going on...
A.
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I presume the 0.16 revs/sec is at the arms, so that's 1.6 revs/sec at the motors using your existing 10:1 gearbox. If you start from step 3 at https://duet3d.dozuki.com/Wiki/Choosing_and_connecting_stepper_motors#Section_How_to_work_out_the_power_supply_voltage_you_need you can work out whether your existing stepper driver voltage (which I presume is 24V) is sufficient to maintain torque at those speeds.
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Hi. We have completed our simulation and it looks like we will need at least 12-15Nm per motor to gain top speed ( 1 pickup per sec ) . Now, according to this, stepper motor is not the best solution so we are switching to servos. I didnt work much with servos but i guess this should be problem solver:
1.) 75VDC -- 200-450W --> 5:1 or 10:1
https://www.teknic.com/model-info/CPM-MCPV-3446P-ELN/Q1):
if i add 10:1 gearbox to this, will i be still be able to make 1 pickup per sec ?
IMHO, there should not be any problems.. It's strong motor and it can be used for future testing.
What do you think ?Q2.): If i understand this correctly, this kind of motor has everything that i need to hook up to duet.
In other words, i just need to add external 72V power supply, let's say 72V / 15A or stronger. Is this
correct ?Q3.) How can i define how much current can be drawn from servomotor. In other words, can i limit motor power consumption to lets say 10A. ?
Q4.) This one is also an option but again, all comes down to pickup speed.
https://www.teknic.com/model-info/CPM-MCPV-3432P-RLN/Arnix
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@arnix said in Suggestion for servo motor --> big delta robot:
Hi. We have completed our simulation and it looks like we will need at least 12-15Nm per motor to gain top speed ( 1 pickup per sec ).
Is that before or after the gearbox? Remember that a 10:1 gearbox will multiply motor torque by ten times.
If you build a 5:1 belt reducer you only need 2-3Nm from the servo.
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I am using the Teknic Clearpath servos on two CNC routers, I even had 3 on one of my 3D printers using a Duet controller. They are strong and very fast, check out their videos. Teknic also sells power supplies. Contact Teknic with your questions they are very helpful and will put in the right direction. Their servos come in various sizes with different torque and RPM combinations, you should be able to get one that doesn’t require reduction.
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@edkirk I forgot to mention their software, connect the servo with USB and you can program, tune and monitor just about everything including torque and rpm so you will know what is going on. Very high quality product and they will take returns if they are in as new condition. Only one drawback- $$$$
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- after gearbox. But that is exactly the thing i would like to discuss. Please look at text below..
@Edkirk
Great info. Thank you. I will contact them tomorrow.
There is one thing that i dont understand with this servomotors...
e.g. if i set 10:1 gearbox and if i get let's say 15Nm on my gearbox shaft, how can i calculate needed RPM and power ? I was looking at calculator that 691175002 suggested but there is bunch of options and i dont know will this work in real time.
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Most of the industry motors used for such applications use 500 - 1Kw motors which is a lot , so i can not understand the purposes for such power. As far as i know, pickup speed is "regulated" with servo motor speed and power ? But do i really need so much motor power ? There must be some catch why they are using such strong motors.
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Btw. yes they are expensive and that's why i would like to find some motor in lower/middle price range, that will do the job.
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@Edkirk
When we define motor and when i buy them i will open new topic on how to hook them to duet. I hope you can help me out with that, i dont wont to burn something
Arnix
- after gearbox. But that is exactly the thing i would like to discuss. Please look at text below..
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What are you building a pick and place robot or a 3D Printer?
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It's pick and place robot. 1,5 meter working radius with optimal 60 pickups per minute. Container is on both sides of the conveyor track and vision system is set to drop to nearest one.
This part is working and at the time, am using steppers for this,
but i would like to implement servos from clearpath.A.
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What type of controller/software are you using? There are various options when using Clearpath Servos, step and direction are well suited for a 3D printer or a cnc router with a controller running a predetermined program using predefined GCode.
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@arnix the reason no one is answering your specific size/power/speed questions is that nobody knows how “picks per minute” translates into speed/acceleration for your system. A pick is not a well-defined load, it’s a performance target. We all have no idea what you need because we don’t know enough about your machine, working loads, tolerance for slower picks when crossing the whole working volume, etc.
The required motor power comes from the max value of (torque * angular speed). You can probably get this from your simulation based on the worst case of picks in many different locations around the working area. Torque in Nm multiplied by speed in rad/sec gives power in watts. If you have the exact ideal gearbox for your application, this wattage is how much motor power you will need. But the farther your gearbox ratio is from ideal, the more you need to oversize the motor to make sure the desired speed/torque point lies within the performance curve for the motor.
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Good morning..
- at the moment am using stepper motors that are connected directly to duet3d board. So just duet board + 24V power supply + motors. Anyhow, this was just for test. Based on your suggestions (when we switch to servo) I will buy what you think it's necessary to make this project work. Please look at text below where i have described project goals. If i understand correctly, every SD model has all in one ( encoder, controller, driver ) or do i need to buy controller separately ? How did you connect your DUET to servo motors ?
@RCarlyle
That was exact our thinking. Thank you for confirmation !.
Let me run some additional tests so I can discus about this, in more details..Regarding robot job:
- robot will sort colored plastic material (similar as the robot from my first post, but with different material ).
- colored object are placed on conveyour track at random order and position
- weight of the object is under 100 grams
- vision system is done and it's tracking objects in realtime so there is no delay. Objects will be spotted and tracked and if the robot can follow 1 pickup per second routine, everything should work.
- tracking diameter is 100 cm.
- please look at the robot on my first post. Goal is the same but with different materials and maybe 10% lower speed.
Arnix
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@arnix said in Suggestion for servo motor --> big delta robot:
- after gearbox. But that is exactly the thing i would like to discuss. Please look at text below..
@Edkirk
Great info. Thank you. I will contact them tomorrow.
There is one thing that i dont understand with this servomotors...
e.g. if i set 10:1 gearbox and if i get let's say 15Nm on my gearbox shaft, how can i calculate needed RPM and power ? I was looking at calculator that 691175002 suggested but there is bunch of options and i dont know will this work in real time.
;-------------------------------------
Most of the industry motors used for such applications use 500 - 1Kw motors which is a lot , so i can not understand the purposes for such power. As far as i know, pickup speed is "regulated" with servo motor speed and power ? But do i really need so much motor power ? There must be some catch why they are using such strong motors.
;----------------------------------
Btw. yes they are expensive and that's why i would like to find some motor in lower/middle price range, that will do the job.
;---------------------------------
@Edkirk
When we define motor and when i buy them i will open new topic on how to hook them to duet. I hope you can help me out with that, i dont wont to burn something
Arnix
@Arnix, you should avoid putting a gearbox on the output shaft of a servo, because then gearbox backlash will matter. Instead, look for a servo that provides the right combination of output torque (high) and RPM (low), perhaps using a built-in gearbox.
Are you sure you need 15Nm output torque? That's a huge amount of torque, equivalent to accelerating a mass of 1.5kg on the end of an arm 1m long. What is the mass of your effector?
Looking through the Clearpath listing, this one is close to your specifications https://www.teknic.com/model-info/CPM-MCVC-3441S-RLN/. It has 13Nm peak torque at low speeds (you don't need high output shaft speeds in your application). But it's Nema 34 size, so you will have to do some redesign to accommodate it. There is the possibility that it might overheat if you demand high torque from it for too much of the time, although I think that's unlikely unless the effector is massive.
- after gearbox. But that is exactly the thing i would like to discuss. Please look at text below..
