Anyone know what model is being used? There are many different versions of the Nema 17… any help would be appreciated.
I am currently using Automation Technology Inc KL17H248-15-4A NEMA 17
Not saying these are the ones to buy, and I am not affiliated with this seller. Just saying they work for my setup.
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We’re ordering ones direct from a chinese manufacturer, Motech Motors. Nema 17, 76 oz/in torque, 4 wire, dual shafted, with rotary encoders.
If you don’t want to use rotary encoders then we recommend the ones from Open Builds: www.openbuildspartstore.com
What is the working alternative to rotary encoders?
I am trying to do this as cheaply as possible by salvaging whatever I can from old RepRap, but my NEMA 17’s are not dual shafted.
Really there is not an option to skip out on all the rotary encoders in all places without other lots of expense or risk of issues. Something the size of farmbot skipping steps and it not being detected is not going to be good as you could get to bending tracks and other things. Fitting lidar or ultrasonic sensors to track moment to pick up if machine is not moving right number of steps is not going to be dead cheep either.
There are magnetic and optical encoders and a few other types. Mechaduino uses magnetic. Magnetic encoders can be used on the back of some NEMA 17 that are technically not dual shaft. If the shaft is exposed enough on the back that you can glue a magnet on to it then it can have a Magnetic encoder installed.
At least for the side drive motors there looks to be enough room to front mount the encoders these would be the absolute critical ones you don’t want working way out of alignment. So from my rough looking not all places in the design mandate dual shafted stepper motors as there are spaces where one encoders could be front mounted. Might be all of the have not fully looked,
I know this from having CNC machines about the same size as the farmbot so two of the motors to be safe from what I can see have to have encoder but is good part is those its either in-front of motor or behind with encoder.
@oiaohm Unfortunately I don’t think my motors’ shafts are long enough to front mount the rotary encoders. Can you recommend any of the magnetic type, or anything that would work on the back of a single shafted motor?
Also, thanks for your informative reply!
Mechaduino is a open source bit using a quite common sensor magnetic sensor with a fairly normal arduino core and motor controller on one board but they still could be built as 3 parts. You need exposed shaft on back of the NEMA 17 to back mount it. Does not have to be dual shaft.
http://tropical-labs.com/index.php/mechaduino
You can get the AS5047D sensor Machaduino uses as a prototyping part. Yes AS5047D correctly aligned and mounted on the back of a NEMA17 that there is enough shaft to glue magnet onto will work. There is a issue with the magnetic sensors is they don’t always give a 100 percent linear results. Does not matter what one you use. Its the fact you have glued magnet to back of motor with so much error and sensor with so much placement error you need to have software run and calibrate out error and from calibrate information generate uniform results. Yes optical rotation sensors are simpler to deal with can skip out on have a brain to provide correct information. Retro fitting arduino+as5047D will get a long way.
I don’t know exactly how farmbot processes the encoders if it could be coded to use AS5047D raw data and use calibration table to produce sanity.
Magnetic Sensor Development Tools AS5047 Magnetic Position Sensor Kit
That is the name of the pre existing prototyping board to with AS5047D already on a board of course its design that you add it to an arduino or the like. Machaduino is one of these things you can either wait for them to release boards or source development parts and assemble something now that does the same thing.
Randman77 magnetics you just have to have enough space to glue magnet on something that is centre on shaft. Now if the NEMA17 you have are all short shafted you could be in trouble anyhow.
Look at Step 7: Attach the gantry motor. Yes it would be possible to use longer bolts into the NEMA17 to hold a front sensor I would call this last kind of result because it not ideal for belt snap. Now if you NEMA are short shaft getting on the gear and the bit to prevent belt from jumping off is going to be tricky. A NEMA17 with the same size shaft as farmbot uses fitting a AS5047D in front should be possible just risking sensor.
Advantage with following what Machaduino project has done they have been testing it with Nema 17 and you are not going to the the only one with that part if you have issues.
The AS5047D way of doing rotary encoder does open up lot more motors to choose from. I can only speak on magnetic sensors I know. There are more out there.
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A source I’ve used before when building a laser engraver/cutter is lightobject.com as they have alot of the parts available. The motors I’m going to be using (along with the encoders from US Digital) are these:
http://www.lightobject.com/NEMA-17-42HSM03-Dual-Shaft-Stepper-motor-P747.aspx
Specs:
Step angle: 1.8 deg
Step per revolution: 200
Phases: 2
Shaft diameter: 5mm
Shaft length: 14mm and 18mm
No. wires: 4
Current: 2A
Holding Torque: 0.57N.M (80oz*in)
Inductance: 3.6 mH
Phase resistance: 1.7 ohms
Detente torque: 200 gcm
Rotor Inertia: 82 g-cm2
Weight: 0.34KG (0.75lb)
Length: 48mm
Yep!
Do you have a complete part number for the Motech motor with mounted encoder? I have not seen this option in their lit.
@roryaronson
Do you have a complete part number for the Motech motor with mounted encoder? I have not seen this option in their lit.
I don’t, you need to contact them to request exactly what you need. The quotes I have received didn’t have a complete part number.
I talked with Mark Li from Shenzhen Motech Motor Co., Ltd. over alibabas chat refering to this motor but without the bracket and dual shaft instead. That is without encoder now. He said, that there is a minimum ordering quantity of 20pcs and that the dual shaft lenght is 10mm. If he tells me the price I’ll post it too.
I suggested him to change the MOQ since there could be more people be interested.
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Since I live near the Gulf of Mexico, I am concerned about the effect of salt air on a farmbot’s stepper motors. I found this article to share with anyone with similar concerns/interests. http://www.designworldonline.com/new-stepper-motors-beat-corrosion-without-seals/
Here is what the person in question (Mark) responded to me:
- The Price is US$75/set, include 360 CRP encoder with Differential output, 5 meter cables (not shileded wire). Based on EXW-item,
- Shipping cost for 6pcs, US$70 by UPS Expedited.
Yes that is the model: mt-1704HS168A, Manufacturer: Motech motor co ltd
I ended up buying a different motor from from a different manufacturer since Motech is charging too much for shipping and for the actual motor ($75 for something that should be half that price). They want big orders and are not much attentive to people like me who wish to place a small order.