Arduino CNC Motion Controllers

I have been examining projects using a gcode parser and step motor controller running on an Arduino. Here are the projects I've come across.


GRBL: ( Simen Svale Skogsrud ) This open source program has been developed to run on a basic Arduino; however, it cannot be compiled using the Arduino IDE. The code is compiled directly using the avr-gcc and downloaded or programmed into the ATmega328 ( Here is another loader ).. The development of GRBL seems very active which is a plus. Take a look at the Github site. I only wished it compiled using the Arduino IDE. For an overview of GRBL including implemented gcodes try here.


If you are interested in trying GRBL, here are some suggestions:

1. Download the Arduino IDE. Can be used to test your Arduino board.
2. Download WinAVR. Can be used to compile GRBL, if you wish.
3. Download the hex file and source for GRBL from GitHub
4. Purchase an Arduino. I would suggest the Duemilanove which can be obtained from Amazon for $20.
5. Purchase a proto shield and wire whatever connector is needed to connect to your driver board.

Notes:

1. Some of the older sketches, like those below, will not compile with the Arduino IDE 1.0, so also download Arduino IDE 023.
2.  I have made sure the drivers on this blog are opto isolated, if yours is not you could do that on the proto shield.

TinyG:


The following Gcode interpreters are directly or indirectly from the RepRap project. The code below has mostly gone dormant, but the code is there to look at and play with.


Reprap_Arduino_Firmware:


Reprap_New_Firmware: ( Chris Meighan )


Reprap_New_Firmware_Arc: ( MMarz )


RSTEP: ( Reza Naima )

Still working on this post

Torsion Box for CNC Router Table

I have been off on other workshop projects for several months, but I am now ready to get back to the CNC Router.

I have been investigating a torsion box assembly bench for general use in my shop. A torsion box provides a stable flat surface on which to assemble projects and furniture. Here are some links:

http://www.finewoodworking.com/PlansAndProjects/PlansAndProjectsArticle.aspx?id=28855

http://www.woodworkinghistory.com/glossary_torsion_box.htm

http://www.scottmorton.com/series/torsion-box-assembly-table/

http://www.google.com/search?q=torsion+box&oe=utf-8&rls=org.mozilla:en-US:official&client=firefox-a&um=1&ie=UTF-8&source=og&sa=N&hl=en&tab=wi&biw=1256&bih=862&tbm=isch#q=torsion+box&um=1&hl=en&client=firefox-a&sa=N&rls=org.mozilla:en-US:official&tbm=isch&fp=1&biw=1152&bih=702&cad=b&bav=on.2,or.r_gc.r_pw.,cf.osb

This last is a google image search of torsion boxes and includes some designed for CNC routers.

While I was investigating, I looked closely at the CNC router table surface that had already been built and found that it was no longer flat. The table surface is an integral part of our CNC router design providing flatness, rigidity and mass. For these reasons the table surface will be replaced by a 32" x 24" x 2.5" torsion box.

What is a torsion box? If you build a box with 6" sides, like a sand box and glue plywood skins, top and bottom, you have a torsion box. Placing the box between two saw horses and a load at the center, the top skin will try to compress and bottom stretch. As long as the spacing between sheets is held fixed the box will resist bending and its strength goes as the cube of the thickness. So we need to build a box with a grid of spacers inside, a honey comb to maintain constant thickness.

Building a torsion box is a chicken and egg problem. For the torsion box to be flat it must be built on a flat surface. So to build a flat surface you must first make a flat surface. Look at the first two links above and you can see how they solved that problem. Things are simpler for us since the surface is small; therefore, instead of jointing and planing 2x4's, I obtained three inexpensive 4ft levels from Harbor Freight for $7 each. These levels will take the place of the 2x4's and eliminate the need for a jointer and planer which I don't have.

Our torsion box will be built from MDF with the sides and core using 1/2" material and the skins 1/4" sheet.

StepTB6560 Step Motor Driver

Schematic

BOM: To be added.

Batchpcb:

http://www.batchpcb.com/product_info.php?products_id=50084&check=33e8b36118a8e7ceaf3179ebcbc71752

Step298 Step Motor Driver

Schematic:

BOM:

Bill of Material for Step298_04C.PCB
On 5/27/11 at 9:25:51 AM
Qty	Label-Value	Pattern	Designation(s)	Mouser
9	FR202	DIODE0.4	D1 D2 D3 D4 D5 D6 D7 D8 D9	583-FR202-B
1	220pf	cap100s	C1	80-C315C221J1G
5	.1uf	cap100s	C10 C4 C6 C7 C9	80-C320C104K1R
1	3300pf	cap100s	C2	80-C320C332J1G
1	.1uf 100v	cap100s	C3	80-C320C104K1R
1	10nf	cap100s	C5	581-SR151C103K
1	220uf 63VDC	C+400D200	C8	647-UHE1J221MPD
2	Fuseholder	Fuse3517	F1	534-3517
1	Heatsink	HS677A	HS1	677-20ABP
1	66506-001LF	XIDC10	J1	517-D2510-6002-AR
1		SIP3	JP1	517-647-01-03
3		SIP2	JP2 JP3 TP1	517-647-01-02
1		LED	LD1	638-HLMP1790
4	1R 1W	AXIAL0.5L	R1 R2 R3 R4	282-1.0-RC
3	10K	AXIAL0.3	R10 R11 R9	299-10K-RC
1	22K	AXIAL0.3	R12	299-22K-RC
1	1K	AXIAL0.3	R13	299-1k-RC
1	240R 1%	AXIAL0.25	R15	270-240-RC
1	715R 1%	AXIAL0.25	R16	270-715-RC
4	330R	AXIAL0.25	R17 R18 R19 R21	299-330-RC
3	1K	AXIAL0.25	R20 R22 R23	299-1K-RC
1	1K5	AXIAL0.25	R24	299-1.5K-RC
2	2K 1%	AXIAL0.3	R6 R7	270-2K-RC
1	2K	AXIAL0.3	R8	299-2K-RC
1	2N3904	TO-92A	T1	512-2N3904BU
3	T-Block-2	MKD2X	TB1 TB2 TB3	538-39880-0402
1	2K	TRIM2	TR1	858-67WR1KLF
1	L298N	L298	U1
1	L297	DIP20	U2
1	6N137	DIP8	U3	512-6N137
1	HCPL2630	DIP8	U4	512-HCPL-2630/31
1	LM317HV	TO-220V	U5	LM317HVT Digikey
1	IC Socket 20p		U2S	517-4820-3004-CP
2	IC Socket 8p		U3S,U4S	517-4808-3004-CP

Batchpcb:

http://www.batchpcb.com/product_info.php?products_id=46128&check=d1866a6ff4033116953019e09b4f316c

Table for CNC Router

I decided that I needed a table on which to both assemble and run the CNC router and which incorporates a heavy stable top made of MDF. The table design is based on Scott's router table shown on this site, http://www.scottmoore.net/projects/router/index.html. The construction uses Kreg pocket screws and glued joints and is made of Poplar. Adjustable feet are incorporated for leveling the table and, possibly, retractable casters. Since Scott's site shows construction details, only a few photos will be shown for this project with an explanation of any differences.

The table height is 37 1/2" with a top surface 24" by 32" by 1 1/2". The home stores carry 1 1/2" square Poplar cut to 36" which was used for the legs.  The top is made from two pieces of MDF glued together with wood glue. A trowel was used to spread the glue in a thin layer and clamps and heavy weights used during bonding.

The construction sequence is as follows:

1. Glue and screw all joints
2. Make two side assemblies as shown in the first picture.
3. Add the four cross members to one of the side assemblies, picture 2.
4. With the base upside down use a doweling jig to drill 7/16 holes in the leg bases, picture 3.
5. Screw threaded inserts ( McMaster 92105A415, 5/16-18) in leg bases.
6. Add levelers (McMaster 23015T62)
7. Turn base right side up and attach top. Note pocket screw holes in first picture for this purpose.

Poplar is soft enough that care must be taken using Kreg screws, so set the torque on the drill to prevent screw tear-out.

Side Assembly

Adding side pieces

Drilling holes for 5/16 threaded insert for levelers using Harbor Freight doweling jig.

Assembled table

Table with CNC Router base end pieces.

SLA7078 Step Motor Driver

A step motor driver using the SLA7078MPR has several advantages over one using the SLA7062M: one, a newer design, two,seems to be more available with a price of $12ea or $8 per ten, three, SLA7078 series has built in sense resistors and,four, the PR version has built in protection circuits.

The design shown below has two version: with and without opto isolation. An idle delay feature has been incorporated which places the motor in half power mode when idle for 10 seconds. This driver does not set motor current by a selection of sense resistors as with the SLA7062 driver. With that driver the reference voltage was fixed, such that a .5 ohm resistor gave 1 amp motor current, so three .5 ohm resistors in parallel gave 3 amps. In the SLA7078 the sense resistors are located in the chip and current settings are adjusted using the trimmer pot. To set the current, a multimeter is attached to the reference signal, JC1 in schematic above, and the trimmer adjusted to a voltage given in the SLA7078 datasheet.

The delay feature uses a 74HCT4538 retriggerable oneshot. A circuit using a LMC555 was investigated which would probably work, but the board space required is about the same as with the 4538 even though only half the 4538 package is used. The circuit works as follows: as long as step signals are arriving, the oneshot stays triggered and the motor stays at full power, but when the step pulses stop, 10 seconds later the motor switches to half power. The first step after a delay should immediately switch the motor to full power. Whether this switching is fast enough will be determined during testing of the prototype driver.

Stepit 4A: Driver using SLA7078MPR with delay

Schematic:

BOM:

Bill of Material for C:\PCB PIC\SLAgm_04C.PCB
On 4/28/11 at 12:18:18 AM
Count	Label-Value	Pattern	Designation(s)	Mouser
1	330uf 50V	C+400D200	C1	647-UHE1H331MPD
1	47uf	C+200D80H31	C2	647-UHE1E470MDD
4	.1uf	cap100	C3 C4 C5 C7	80-C320C104K1R
1	47uf 50V	C+200D100H31	C6	647-UPW1E470MDD
1	15uf tant	cap100	C8	581-TAP156K016SCS
1		DIP6	DS1	774-2063ST
1		XIDC10	J1	517-D2510-6002-AR
2		SIP2	JC1 JP1	517-647-01-02
1		SIP3	JP2	517-647-01-03
4	10K	AXIAL0.25	R1 R5 R6 R8	299-10K-RC
1	4k7	AXIAL0.25	R2	299-4.7k-RC
1	1M	AXIAL0.25	R3	299-1M-RC
3	1K	AXIAL0.25	R4 R7 R9	299-1K-RC
1	10K	SIP8	RN1	265-10K-RC
2	BC327	TO-92A	T1 T2	512-BC32740BU
1	BC547	TO-92A	T3	512-BC547CBU
1		TB508A_2	TB1	538-39880-0402
2		TB508-3	TB2 TB3	538-39880-0403
1	1K	TRIM2	TR1	858-67WR1KLF
1	SLA7078MPR	SLA7078	U1
1	74HCT4538	DIP16	U2	595-CD74HCT4538E
1		DIP16 Socket		517-4816-3004-CP

Next will be the schematic and BOM for the opto-isolated version, Stepit 4

Stepit 4: Driver using SLA7078MPR with opto-isolation, regulator and delay

Schematic:

BOM:

Bill of Material for C:\PCB PIC\SLAgm_05A.PCB
On 4/30/11 at 2:23:09 PM
Count	Label-Value	Pattern	Designation(s)	Mouser
1	330uf 50V	C+400D200	C1	647-UHE1H331MPD
6	.1uf	cap100	C10 C4 C5 C6 C8 C9	80-C320C104K1R
1	47uf	C+200D80H31	C2	647-UHE1E470MDD
1	47uf 50V	C+200D100H31	C3	647-UPW1E470MDD
1	15uf	cap100	C7	581-TAP156K016SCS
1	FR202	DIODE0.35	D1	583-FR202-B
1		DIP6	DS1	774-2063ST
2	Fuse Holder	Fuse3517	F1	534-3517
1	Socket IDC 10p	XIDC10	J1	517-D2510-6002-AR
2		SIP2	JC1 JP1	517-647-01-02
1		SIP3	JP2	517-647-01-03
1	HLMP1790	LED	LD1	638-HLMP1790
1	240R 1%	AXIAL0.25	R1	270-240-RC
1	1M	AXIAL0.25	R10	299-1M-RC
5	1K	AXIAL0.25	R11 R12 R6 R7 R9	299-1K-RC
4	10K	AXIAL0.25	R13 R14 R15 R16	299-10K-RC
1	720R 1%	AXIAL0.25	R2	270-720-RC
3	330R	AXIAL0.25	R3 R4 R5	299-330-RC
1	4K7	AXIAL0.25	R8	299-4.7K-RC
1	10K	SIP8	RN1	265-10K-RC
2	BC327	TO-92A	T1 T2	512-BC32740BU
1	BC547	TO-92A	T3	512-BC547CBU
1		TB508A_2	TB1	538-39880-0402
2		TB508-3	TB2 TB3	538-39880-0403
1	1K	TRIM2	TR1	858-67WR1KLF
1	SLA7078MPR	SLA7078	U1
1	74HCT4538	DIP16	U2	595-CD74HCT4538E
1	6N137	DIP8	U3	512-6N137
1	HCPL2631	DIP8	U4	512-HCPL-2630/31
1	LM317HV	TO-220V	U5	LM317HVT Digikey
2	IC Socket 8p		U3S U4S	517-4808-3004-CP
1	IC Socket 16p		U2S	517-4816-3004-CP