The BOM contains three sections.
- Components
- Fasteners
- Printed Parts
The components are the most complex parts to get hold of (and the most expensive). In this part three, we will get hold of them all or get some alternatives. As mentions in the previous parts, I want to avoid using the RAMPS electronics. For this reason, I will not buy the following items from the components list:
- Arduino Mega (Orginal)
- RAMPS V1.4
- Stepper Motor Driver TB6560
In my shelf I found some TB6600 Driver I’ll use them and to control these drivers I will use a Teensy 4.0 for now.
Issues on GitHub
In Issue 7 is there is a discussion about the BOM, but somebody has really helped out. In Summary:
The Rods are M8 (8 mm diameter)
There is a confusion for the rods because the length in stated by the BOM and the length in the CAD-Model is different.
| BOM | CAD |
| 42 mm | 50 mm |
| 80 mm | 80 mm |
| 114 mm | 121 mm |
| 134 mm | 140 mm |
I’ll use the length given from the CAD-Model because there I can comprehend where the length is coming from. If I’m wrong, I have to order the other ones.
In Issue 42 there is listed an alternative Motor for the “Nema 23, 112 mm, Ø8 mm flat shaft” because this one has no more resellers. It is the “Nema 23 stepper 3Nm 4,2A Ø 10 mm shaft”. This Motor requires more current and has the same torque, and of course, they have another shaft. This means that is important to change the pulley amount of BOM ID 21 (Pulley T5, Bore 8 mm, 14 teeth, 17 mm width) from three to one. And we have to add two pulleys from type Pulley T5, Bore 10 mm, 14 teeth, 17 mm width.
| BOM ID | BOM | Quantity |
| 21 | Pulley T5, Bore 8 mm, 14 teeth, 17 mm width | 1 |
| 34 | Pulley T5, Bore 10 mm, 14 teeth, 17 mm width | 2 |
| 35 | Nema 23 stepper 3Nm 4,2A Ø 10 mm shaft | 2 |
My Issues
Beside the already issues, there are covered on the GitHub page. I have quite a difficult experience myself. I’ll address two main problems that I had, finding the right components.
Issues with “Self oil bearing”
The self oil bearing (BOM-ID 30 / 31) aren’t bearing at all. I could not find them, so I looked in the user manual and looked for the BOM ID 30.
They are needed to create a space between the bearing and the nut. In the CAD-Model, you can have a better understanding what this part does. The brown sleeve is the “Self oil bearing”.
BOM ID 30 is: M5 Sleeve Ø 8 mm and length 10 mm
BOM ID 31 is: M8 Sleeve Ø 12 mm and length 20 mm
And the amount from the M8 Sleeves are wrong. In the CAD model, there are two sleeves in use. How I see it, there isn’t are high mechanical forces at these sleeves. At first, I want to print the sleeves, too. If they fail, I will change them for some metal ones.
Motors
Finding the same motors listed in the BOM is difficult and expensive. Even if I find the correct motor, it isn’t the cheapest match anymore. This is especially true for the NEMA 14 Motor (BOM ID 10). So, we have to find matching inexpensive alternatives. But what are the important attributes to look after?
- Format (NEMA X and length)
- Torque
- Weight
The current consumption isn’t relevant for this. If we found a motor with the same torque and half of the consumption, this would be a great fit. I’m looking at first for a mechanical alternative that fits inside the space from the motor and can move with the same strength. Because the motor can be used in the Top of the arm, the weight is important. When the motor weights more and has the same torque, the hole arm can only lift less, because of the extra weight from the motor.
Torque
In the beginning, I had problems with the “g · cm” specification for the stepper motors. Some motors have Nm as unit and some “g · cm” (gcm). The first task is to look into this.
I did not explain the conversion, because I did not know why the stepper motors engineers thought, that giving a specification where you have the multiple with the acceleration due to gravity is a good specification.
Or you make yourself a favor and use this website. They will calculate this for you.
Specifications
Here we will find all the specs from the Motors they are in the BOM
BOM ID 1: Stepper Motor SM42HT47-1684 1,8º step, 1,6 A, 3600 g · cm
Data sheet
| Motor | SM42HT47-1684 |
| Torque | 0,353 Nm |
| Format | Nema 17 |
| Length | 38 mm |
| Weight | 0.280 kg |
| Current | 1.68 |
| Steps | 1.8° |
| Shaft Ø | 5 mm |
| Shaft len. | 24 mm |
BOM ID 10: Stepper Motor SM35HT36-1004A, 1.8° step, 1A, 1400 g · cm
Data sheet
| Motor | SM35HT36-1004A |
| Torque | 0,137 Nm |
| Format | Nema 14 |
| Length | 36 mm |
| Weight | 0.180 kg |
| Current | 1 A |
| Steps | 1.8° |
| Shaft Ø | 5 mm |
| Shaft len. | 21 mm |
BOM ID 11: Stepper Motor nema 17 SM42HT33-1334 , 1,8º step, 1,33A, 2200 g · cm
Data sheet
| Motor | SM42HT33-1334 |
| Torque | 0,216 Nm |
| Format | Nema 17 |
| Length | 33 mm |
| Weight | 0.220kg |
| Current | 1.33 A |
| Steps | 1.8° |
| Shaft Ø | 5 mm |
| Shaft len. | 24 mm |
Selection
Originally, I wanted to use for every Nema 17 the same Motor type but the Gearbox for a Nema and a Nema with Gearbox costs around about the some. So I’ll stick which the original Nema 17 with Gearbox as the BOM states (BOM ID 8) and use for the Nema 17’s the 42BYGHW609 Stepper Motor, because of the length of 40 mm I have change the original designs in the future.
| Motor | 42BYGHW609 |
| Torque | 0,392 Nm |
| Format | Nema 17 |
| Length | 40 mm |
| Weight | 0.240 kg |
| Current | 1.7 A |
| Steps | 1.8° |
| Shaft Ø | 5 mm |
| Shaft len. | 24 mm |
And for the Nema 14 I found the “B089Y48SWK” – this is probably a spelling mistake by the reseller. I’ll update this to the correct one if I get one. Because I could not find this product elsewhere but the specs are matching. So I hope this is one I need.
| Motor | B089Y48SWK |
| Torque | 0,210 Nm |
| Format | Nema 14 |
| Length | 44 mm |
| Weight | 0.200 kg |
| Current | 1 A |
| Steps | 1.8° |
| Shaft Ø | 5 mm |
| Shaft len. | 20 mm |
Price point: Components
This is a common question for this robot arm. I attach a list from all the components I purchased for this project.
This price for the components alone is: €374.48
I’m certain that it is possible to lower the price quite a bit if you can purchase all items by AliExpress. But Unfortunately for me, my country (Germany) has raised the taxes for imports from China. For me, there is no benefit to purchase them there.
Components BOM for this project
Please be aware that I changed some parts from the BOM and this is not the original BOM. Some parts are updated and some are complete replaced, especially the electronics. Please notify me if some links are outdated or create an issue on GitHub.
BOM ID
Description
Quantity
Price1
Supplier2
4
Power Supply 24V 480W
1
32.99
Amazon
6
Power converter 24V to 12V
1
3.99
Amazon
7
Servo Motor 180° 55G TORQUE=13KG/CM
1
21.99
Amazon
8
Gear Ratio 5:1 Planetary Gearbox Nema 17 Stepper 17HS19-1684S-PG5 ( step 0,35º , 2Nm, 1,68A)
1
34.99
Amazon
15
Ball Bearing 608ZZ 8mm x 22mm x 7mm
10
1.10
M.D.
16
Ball Bearing 625ZZ 5mm x 16mm x 5mm
8
0.45
M.D
17
Ball Bearing 624ZZ 4mm x 13mm x 5mm
9
0.45
M.D.
18
Ball Bearing 623ZZ 3mm x 10mm x 4mm
3
0.50
M.D.
19
Brass insert M4 x 8mm (Pack of 10)
1
4.39
Ebay
20
Brass insert M3 x 6mm (Pack of 20)
1
5.99
Ebay
21
Pulley T5, Bore 8mm, 14 tooth, 17mm width
1
3.06
Aliexpress
22
Pulley T5, Bore 5mm, 10 tooth, 17 mm width
2
3.27
Aliexpress
24
ZCOUPLING STEEL 5 TO 8 mm rigid
1
8.50
M.D.
27
Power supply cable IEC 1,8m
1
7.99
Amazon
29
Cable Ties
10
5.99
Amazon
32
Wood Base - 550mm x 550mm x 16mm
1
-
H.S.
333
Breco belt T5, 16mm width, L 250cm
1
13.80
M.D.
34
Pulley T5, Bore 10mm, 14 tooth, 17mm width
2
3.27
Aliexpress
35
Nema 23 stepper 3Nm 4,2A Ø 10 mm shaft
2
25.21
Ebay
36
Chrome steel smooth bar 140mm M8
1
1.10
M.D.
37
Chrome steel smooth bar 121mm M8
1
1.01
M.D.
38
Chrome steel smooth bar 80mm M8
1
0.80
M.D.
39
Chrome steel smooth bar 50mm M8
1
0.65
M.D.
40
Stepper Motor Driver DM 556 5,6 A
2
17.29
Ebay
41
Stepper Motor Driver TB 6600 4 A 9 - 42V
4
9.99
Ebay
42
Teensy 4.0
1
24.45
Amazon
43
Nema 17 Stepper Motor 42BYGHW609, (1.7A, 1.8°, 4000 g·cm)
2
14.99
Ebay
44
Nema 14 Stepper Motor, B089Y48SWK, (1A, 1.8°, 2141 g·cm)
1
15.99
Amazon
1000
End Splices
~100
-
1001
AWG20 Cable Red 2m
1
-
1002
AWG20 Cable Black 2m
1
-
1003
Arduino Nano
1
-
1004
Arduino Nano Breakout Board
1
-
1005
10 meters 4 channel RGB Wire (awg21)
1
-
1006
10 meters 4 channel RGB Wire (awg18)
1
-
H.S. – local hardware store
M.D. – Mechatronic Dold is a local Store. It would make me glade if you purchase some of your items there. :)
H.S. – local hardware store
M.D. – Mechatronic Dold is a local Store. It would make me glade if you purchase some of your items there. 🙂
1 – Missing, using instead the 43
2 – Missing, using a Teensy 4.0. See BOM ID 42
3 – Missing, using 4x TB 6600 and 2x DM556
5 – Missing, don’t use such a board
9 – Missing, there are no resellers. I’m using 35 instead
10 – Missing, using instead the 43
11 – Missing, I’m using 36 instead
12 – Missing, I’m using 37 instead
13 – Missing, I’m using 38 instead
19 – Brass insert length checked in the CAD model
12 – Brass insert length checked in the CAD model
23 – Missing, I’m using 39 instead
25 – Missing because I’m not using the tb650 driver and need a custom housing
26 – Missing because I’m not using the tb650 driver and need a custom housing
28 – Missing because I’m using a Teensy, and they need a micro USB cable.
30 – Missing, See Issue. They’ll be mentioned in the printed part section.
31 – Missing, See Issue. They’ll be mentioned in the printed part section.
Prices by Seller:
Amazon: €129.94
eBay: €99.85 + €4.95 shipping
M.D.: €45.86 + €10 shipping
AliExpress: €21.20 incl. shipping
Thinks not included: 42, 43, 41, 29
Next part, the BOM: Fasteners
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