OpenLeg - Dynamic Robotic Leg

843

4

2

OpenLeg started as my Senior Design project at UIUC. The goal of the project is to provide a fully open source robotic leg capable of fast dynamic movements for research and development of quadrupedal robots. OpenLeg is intended to make development of legged robots and associated algorithms accessible to hobbyists and researchers with tight schedules or budgets. This video shows the leg in action during it's first tests.

The following Instructable will provide the complete Assembly process step-by-step of how to assemble your very own OpenLeg and Development stand shown above!

Electronics Overview

OpenLeg is primarily controlled by an ODrive along with and accompanying python script. The ODrive takes care of the difficult BLDC motor control and allows a position or torque to be commanded to each joint. The ODrive controls two high torque 60KV BLDC motors to drive the hip and knee joints.

OpenLeg uses magnetic encoders on each motor to allow for precise and accurate control. The encoders are capable of absolute output but currently the project only uses the quadrature output of the encoders and must be started in the same position each time for position control to be correct.

The Development stand houses two 12V 60A power supplies which are wired in series in order to provide 24V to the leg.

Mechanical Overview

The leg is almost fully made out of 3D printed parts, with the exception of the knee motor pulley, a few belts, and the carbon fiber tube that makes up the majority of the lower leg.

All parts are designed to fit on a standard Prusa i3 printer or clone. Personally, I used the Afinibot A3 for printing most of my parts. In the photos of my senior design project, all black and silver printed parts are PLA and all white parts are PETG. This was simply because of the resources I had available already. One part which holds the idlers inside the upper leg is printed in bridge nylon filament to make sure it was strong enough, but I have edited the part already so that it will probably work with PLA or PETG as well.

Let's get started!

Supplies:

The OpenLeg Part List can be found in the Assembly guide on the OpenLeg GitHub. The guide also serves as an alternative method of viewing the assembly steps.

OpenLeg Assembly Guide

Teacher Notes

Teachers! Did you use this instructable in your classroom?
Add a Teacher Note to share how you incorporated it into your lesson.

Step 1: Upper Leg Assembly

Parts needed for upper leg:

  • 1x LegShell 3D Print
  • 1x LegCover 3D Print
  • 2x 1,65mm_spacer 3D Print
  • 2x T5_30T_Pulley 3D Print
    • (Use nylon if possible to last longer, I used PLA for Senior Design though)
  • 1x T5_12T_Pulley 3D Print
    • (Use nylon if possible to last longer, I used PLA for Senior Design though)
  • 1x IdlerBentConnector 3D print
    • (Use nylon if possible, I used Bridge Filament for Senior Design)
  • 1x 6354 Size Motor
  • 1x AS5047D Magnetic Encoder development board
  • 4x Half inch hex bearings
    • I bought these from VEX - https://frchobby.en.alibaba.com/product/604681419... These and the hex shaft are overkill but they were a last minute change to be safe after the set screws on a 5mm shaft kept rotating. One benefit is that these work well with 3D printed parts, and the 5mm shaft required metal pulleys.
  • 2x Half inch hex shaft of length 58mm
  • 1x Half inch hex shaft of length 94mm 2x Half inch hex shaft collars
  • 1x Heavy Duty Half inch hex shaft collar
    • I bought this from AndyMark. If you plan to use the 3D print provided as is then you will need the same one, not the one from VEX - https://tinyurl.com/y46wyf65
  • 2x 10mm wide,5mm bore idler pulleys
  • 2x 5mm steel shaft of length 30mm
    • I bought the shaft from Amazon - https://tinyurl.com/y46wyf65 You will have to cut the shaft to length. I do not suggest trying to use a saw, it would take forever. I suggest using a dremel with a cutting wheel.
  • 4x M4 8mm screws
    • These are for holding the motor in. Any screw length that holds well and doesnt hit the motor coils is fine
  • 4x M2.5 8mm Screws
    • These are for holding on the encoder. 8mm is just an estimate, anything around that should work fine, there is plenty of room for the screw to extend out of the holes.
  • 3x M4 30mm screws
    • These are for holding the upper leg to the adapter and 84T Spur gear.
  • 3x M3 35mm screws
    • These are for tensioning the idler pulleys on the first stage of the transmission in the upper leg.
  • 3x M3 square nuts
    • These are for the M3 x 35mm screws to thread through.
  • 1x Diametrically magnetized magnet 6mm x 2mm
    • This magnet is for the encoder. I purchased mine from DigiKey - https://tinyurl.com/y46wyf65 Make sure the magnet is diametrically polarized, not axially polarized.
  • 1x 12T Motor Pulley for T5 Belt, 8mm bore
    • I purchased a pulley made for XL belt instead of T5 because I could not find an affordable T5 belt that would arrive fast enough. Here is the link to the belt I used- https://tinyurl.com/y46wyf65 If you can source a T5 12mm pulley that would be ideal, but the XL works well as the pitch is very close.

Step 2: Upper Leg Assembly — 1

Upper Leg Assembly Step One:

Time to jump right in to assembly. First, solder wires to the encoder of about 30cm in length. Connect wires to the A, B, 5V, and GND pins. These will later run out of the leg to the motor controller for the knee joint.

Connect the encoder to the Leg Shell using 4 M2.5 screws. (M3 can be forced through the dev board as well). The Leg Shell is made for M3 holes to thread in, M2.5 screws will need locknuts on the end.

ATTENTION: The spacers are not shown, but you will need to space the PCB away from the shell by about 1.5mm to 2mm for it to be at the proper distance from the magnet. The Encoder IC should be about 0.5mm to 1mm from the magnet.

Step 3: Upper Leg Assembly — 2

Glue the magnet to the back of the motor in the center using Super Glue or epoxy.

Make sure to get it centered! The magnet is used by the magnetic encoder to sense the exact angle of the leg, if the magnet is not centered, this measurement will not be correct.

Step 4: Upper Leg Assembly — 3

Attach the metal 12T pulley to the Motor Shaft, Align one of the set screws with the keyed part of the shaft for a good hold.

The distance between the face of the motor and the pulley can be adjusted to line up with the idler pulleys later in the assembly.

Step 5: Upper Leg Assembly — 4

Connect the motor to the Leg Shell using four M4 by 8mm Screws. Make sure that the wires coming from the motor are facing out of the Leg shell opening as shown in Upper leg assembly 1.

Step 6: Upper Leg Assembly — 5

Insert two of the hex bearings into the Leg Shell. The bearings should be a press fit and may require using a clamp, assembly press, or mallet to get them in.

Step 7: Upper Leg Assembly — 6

Insert the three square M3 nuts into the locations in the Leg Shell shown below. The shell is designed for the nuts to be heated and pressed into place while slightly melting the plastic around them so that they hold in place well.

Next, screw the 35mm long M3 Screws into the nuts from the outer side of the leg shell as shown below. These screws will be how you tension the belt between the motor pulley and the first shaft.

Step 8: Upper Leg Assembly — 7

Create the Idler Pulley Sub-Assembly

  • Cut two pieces of 5mm Steel Shaft to a 30mm length
  • Insert the shaft pieces into each side of the Idler Bent Connector
  • Slide the Idler Bearings onto the two shaft pieces as shown below

I suggest putting glue in the holes of the Idler Bent Connector before putting in the shaft so that they do not fall out later.

Step 9: Upper Leg Assembly — 8

Create the first stage pulley sub-assembly

  • Cut a Piece of hex shaft to 58mm
  • Clamp the shaft collar about 9.5mm from the end of the shaft as shown below
  • Slide on the 12T Printed Pulley and the 30T printed pulley in the order shown below
  • Add the 1.65mm spacer next to the shaft collar. This goes on the side that will face the bearing.

Step 10: Upper Leg Assembly — 9

Create the second stage pulley sub-assembly

  • Cut a Piece of hex shaft to 58mm
  • Clamp the shaft collar about 9.5mm from the end of the shaft as shown below
  • Slide on the 30T printed pulley on the side shown below
  • Add the 1.65mm spacer next to the shaft collar. This goes on the side that will face the bearing.

Step 11: Upper Leg Assembly — 10

Insert the sub-assemblies from the previous steps into the leg.

  • Start by getting the first stage belt around the motor shaft. If the pulley on the motor shaft is not too far from the motor the belt can be slid around it.
  • Then insert the Idler sub-assembly. Keep the screws tensioning the idler sub-assembly loosened.
  • Insert the first stage pulley sub-assembly. Put the second stage belt around the 12T pulley before inserting so that it is ready for the next step.
  • Wrap the belt over the idlers and around the 30T pulley as shown below.
  • Insert the second stage pulley sub-assembly. The belt is supposed to be tight. You will have to get the belt from the 12T pulley around the 30T pulley of the second stage and then insert the shaft into the bearing.

Step 12: Upper Leg Assembly — 11

Prepare the upper leg cover with the bearings as shown above.

Note: This will not be put on until after the lower leg assembly is finished and put onto the upper leg.

Step 13: Upper Leg Assembly — 12

Prepare the hip shaft assembly.

  • Connect the heavy duty shaft collar to the end of the the 94mm shaft. The collar should be flush with one end.
  • Slide the shaft through the Leg to Hip Adapter print as shown below. If you’d like to be able to loosen the collar later you can line up the screw with the hole in the print. However, you probably will never do this. The collar will be very difficult to push into the print, this is on purpose so that it is a very rigid connection. Use an arbor press, clamp, or vise if you can.

Step 14: Upper Leg Assembly — 13

Connect the leg cover to the hip shaft assembly. Use three M4x30mm screws. The screw heads face the inside of the leg shell as shown below. Insert them into three of the six holes spread out evenly as shown below. The other three screws will be put in later from the other direction when the gear is put on. (So that the two screw holes in the leg cover are still accessible for now)

All done with this assembly for now! Move on to the lower leg and then we will return to connecting the two.

Step 15: Lower Leg Assembly

Parts needed for lower leg:

  • 1x LowerLegAdapter 3D Print
    • (PLA or PETG are sufficient for this, Nylon would be better)
  • 1x LowerLegFoot1 3D Print
    • I suggest using TPU for this part. If you can’t get your hands on some flexible filament I suggest somehow trying to cover whatever you use in a rubber material
  • 1x Carbon Fiber Tube of length 130mm, OD 25mm, ID 23mm
  • 2x M4 x 45mm screws
    • These screws are for strengthening the lower leg adapter, the length does not have to be exact
  • 4x M4 x 10mm screws
    • These screws are for connecting the carbon fiber tube to the lower leg adapter
  • 6x M4 Square nuts
  • 1x 5mm steel shaft of length 30mm

Step 16: Lower Leg Assembly — 1

Prepare the carbon fiber tube

  • Cut the tube to a length of 130mm, look up how to cut carbon fiber tube if you haven’t done it before
  • Drill the two 4mm holes through the tube. The holes should be centered on the side of the tube, the holes are 10mm apart from each other and the first hole is 6mm from the end. Refer to the pictures above.

Step 17: Lower Leg Assembly — 2

Insert the six M4 square nuts into the lower leg adapter 3D print

The first two nuts get slid into the side of the adapter until they line up with the holes as in the picture below

The next four nuts get slid into the circular part of the adapter until each one lines up with its respective hole. Slide in the deeper nuts first and use something like a hex key to push them until they line up with the holes, once aligned, slide in the next nut until it lines up with its hole, be sure not to push it too far!

Step 18: Lower Leg Assembly — 3

Screw in the two M4 x 45mm screws to the circular face of the adapter. These screws are for strengthening the plastic adapter.

Step 19: Lower Leg Assembly — 4

Attach the Carbon Fiber Tube to the lower leg adapter using four M4 by 10mm screws. I suggest using thread locker on these.

Step 20: Lower Leg Assembly — 5

Insert the foot 3D print into the end of the carbon fiber tube. This should be a press fit. If the foot is too loose and slips out, try wrapping tape around the part that inserts into the tube until it causes a tight fit.

Step 21: Lower Leg Assembly — 6

Press in the 5mm shaft to the side of the adapter. This should be a very tight press fit. This shaft acts as a hard stop in conjunction with the cut-out in the leg cover so that the lower leg does not crack the leg shell of the upper leg.

All done with the lower leg assembly! That was fast! Now let’s connect it to the upper leg.

Step 22: Connecting the Upper and Lower Leg Assemblies

Parts needed for connecting the upper and lower leg:

  • 1x 84T_SpurGear 3D print
    • (Use nylon if possible to last longer, I used PLA for Senior Design though) OR - purchase the metal gear that this is based on from VEX - https://www.vexrobotics.com/1-2-hex-bore.html (84 Tooth Aluminum Spur Gear) It’s slightly different but if you’re making this project I trust you to figure out how to make it work. (It would be better than printing but too expensive for me to decide to use considering the print works well too).
  • 1x Leg_To_Hip_Adapter 3D Print
  • 3x M4 30mm screws
    • These are for holding the upper leg to the adapter and 84T Spur gear. They are to reduce backlash by not allowing any of the 3 components to rotate independently due to play on the shaft.
  • 7x M3 20mm screws
    • These are for holding the cover to the shell. For a very strong hold you can also thread in M4 Screws since the screws just thread into the 3D printed part. I suggest doing this if you will be taking them in and out multiple times.

Step 23: Connecting the Upper and Lower Leg Assemblies — 1

Slide the lower leg adapter onto the shaft of the second pulley stage as shown in the pictures. Be sure to line up the holes in the adapter with the holes in the pulley.

Step 24: Connecting the Upper and Lower Leg Assemblies — 2

Insert the screws that hold the lower leg adapter to the 30T Pulley. These screws are for reducing backlash. They ensure that the lower leg adapter and the pulley rotate the same amount regardless of whether each of them has any play on the shaft.

Step 25: Connecting the Upper and Lower Leg Assemblies — 3

Connect the leg cover assembly. Make sure the motor wires and encoder wires are coming out of their respective holes in the cover.

Step 26: Connecting the Upper and Lower Leg Assemblies — 4

Connect the 84T Spur gear as shown below. Slide the gear over the hip shaft with the small spacer extrusion facing away from the leg. Use three M4x30mm screws to hold the gear on, through the three unused holes in the leg to hip adapter.

The knee joint is complete! Not much fun with only one joint though, In the next section we will walk through building the hip joint.

Step 27: Hip and Gantry Assembly

Parts needed for the Hip and Gantry assembly:

  • 1x Gantry 3D Print
  • 1x Hip 3D Print
  • 1x AS5047D Magnetic Encoder development board
  • 1x 6354 Size Motor
  • 4x M2.5 5mm Screws
    • These are for holding on the encoder.
  • 4x M2.5 5mm Standoffs
    • These are for holding on the encoder.
  • 4x M2.5 5mm x 0.5mm washers
    • These are for holding on the encoder.
  • 4x M2.5 nuts
    • These are for holding on the encoder.
  • 4x M4 8mm screws
    • These are for holding the motor in. Any screw length that holds well and doesnt hit the motor coils is fine
  • 1x Diametrically magnetized magnet 6mm x 2mm
  • 4x M4 Square nuts
    • These are for holding the hip to the gantry
  • 4x M4x35mm Screws
    • These are for holding the hip to the gantry
  • 1x 11T motor pinion gear
  • 1x Custom 3mm to 2mm shaft key
    • This a custom made part to adapt the 3mm keyway in the motor shaft to the 2mm keyway.
  • 4x V-wheels
  • 4x M5x1mm Washers
    • For properly spacing the gantry from the linear rail
  • 4x M5x50mm Screws
    • For holding the V-wheels to the gantry 50mm is only needed if you plan to attach a belt to the gantry to measure the height of the leg on the development stand, If you do not, they can be shorter.
  • 4x M5 lock nuts
    • For holding the V-Wheels to the gantry

Step 28: Hip and Gantry Assembly — 1

(Distances in mm)

Create the 2mm to 3mm key for the motor shaft and insert the key onto the shaft

Make the key about as long as the keyway. These distances are estimated, When I made mine I milled it slightly oversized and the grinded it until the gear just fit by using a mallet to hit it onto the shaft. This allowed me to rely on the press fit and not need retaining rings

Press the key into the motor shaft using vice grips or pliers.

If you’d like to change the shape of the key to be a T shape instead of an L shape feel free to, I used an L shape because it was easier and the fact that the key was not centered on the shaft made the gear hold its place better.

Step 29: Hip and Gantry Assembly — 2

Install the pinion gear on the motor shaft. You will have to use a mallet or press if you have made the key to a press fit tolerance. If not, you will need retaining rings on each end of the gear. The 11T gear is wider than the 84T gear so there’s not exact distance it has to be from the face of the motor.

Step 30: Hip and Gantry Assembly — 3

Super glue or epoxy the magnet to the center back of the motor, same as for the previous motor. If you have to hammer the pinion onto the shaft make sure you do that step first.

Step 31: Hip and Gantry Assembly — 4

Attach the motor to the Hip 3D print using four M4x8mm screws as shown below. The hip print has slots to adjust the gear center to center distance later if needed.

Step 32: Hip and Gantry Assembly — 5

Insert the two hex bearings into the Hip 3D print as shown below.

Step 33: Hip and Gantry Assembly — 6

Press the four square M4 nuts into the Gantry 3D print as shown below. The print is designed for the nuts to be heated before being pressed in to slightly melt the plastic around them for a good hold.

Step 34: Hip and Gantry Assembly — 7

Attach the encoder to the Gantry 3D print using four M2.5x5mm standoffs, four M2.5x4mm screws, four M2.5 washers, and four M2.5 nuts. If you have the motor slid as far up on the hip as the slots allow, then the top face of the encoder should be 38.25mm from the top face of the Gantry as shown below. The same wires as the first encoder must be broken out (A, B, 5v, GND).

Step 35: Hip and Gantry Assembly — 8

Attach the V-wheels to the Gantry as shown below. For this we will need the following:

  • 4x M5x50mm Screws
  • 4x 6mm M5 Spacers
  • 4x 1mm M5 washers
  • 4x M5 locknuts
  • 4x v-wheels

The 6mm Spacer goes on first, then the Washer, the v-wheel, and the locknut. If you want to use a 7mm spacer that’s fine too, it is just less common to find at a hardware store so I used 6mm with a washer.

The three hole choices you have are for adjusting the spacing to get the right fit around the v-slot extrusion. The outer holes (the ones I used) are what the distance should be if everything is manufactured properly.

Step 36: Hip and Gantry Assembly — 9

Connect the Hip Assembly to the Gantry assembly using four M4x35mm screws as shown above.

Step 37: Connecting the Leg to the Hip and Gantry

Parts needed for Connecting the Leg to the Hip:

---

Slide the hex shaft of the leg assembly through the bearings in the hip assembly. Before the shaft is all the way in, place the shaft collar where the shaft will come out of the second bearing so that the shaft slides into the shaft collar (much easier to do with the gantry detached from the hip).
When the shaft is through the shaft collar, tighten the shaft while making sure that there is no play back and forth axially on the shaft.

That’s it! The leg is mechanically complete!

Step 38: Development Stand Assembly

Parts needed for Development Stand assembly:

I got the T-slot and other 2020 hardware at ZYLTech - http://www.zyltech.com/store/aluminum-extrusion-hardware/2020-t-slot/

  • 4x 460mm 2020 T-slot
  • 6x 420mm 2020 T-slot
  • 4x 125mm 2020 T-slot
  • 2x 160mm 2020 T-slot
  • 1x 1000mm 2020 T-slot
  • 1x 1500mm 2060 V-slot
  • 46x 2020 T-slot Corner Bracket
    • This would be the best amount. However I used less for cost reasons, I’ll let you decide where to leave them out if you use less. I also 3D printed some of mine to save cost.
  • 112x M4x8mm Screws
    • This number will depend on how many corner brackets you choose to use
  • 112x M4 2020 T-slot Sliding Nuts
    • This number will depend on how many corner brackets you choose to use Called Hammer Nuts at ZYLTech 1x 460mm Square sheet of pegboard This will be for mounting the power supplies to.
  • 1x 460mm x 200mm Sheet of ⅛ inch plastic, Polycarbonate or ABS
    • I had to use Acrylic for this because it’s what I had. Acrylic is very brittle though. Keep in mind you will need a laser cutter or water-jet cutter or router for this part, if you don’t have access to one of these and don’t want to cut it by hand then you might want to get creative with this part.
  • 1x 6in x 18in metal sheet.
    • Ideally this would be 460mm instead of 18in but I used what I could find at a hardware store in the US for this.

---

The mechanical assembly of the development stand is fairly straightforward so this section will mostly consist of renders of the final product rather than incremental steps showing it built up.

Step 39: Development Stand Assembly — 1

Start with cutting all of the 2020 T-slot pieces as shown above.

Step 40: Development Stand Assembly — 2

Prepare the pegboard

The pegboard (shown above) is 460mmx460mm, note the extra holes drilled near the corners for mounting it to the Frame. These holes should be 10mm from the edges and fit an M4 screw.

Step 41: Development Stand Assembly — 3

Prepare the Metal Plate

Drill four holes in the plate for mounting to the frame. If you are using an 18 inch plate, the holes must be 9.95 mm from the right and left side shown below to match up with the frame.

Step 42: Development Stand Assembly — 4

Prepare the Plastic Plate for holding the electronics:

Using the Plastic Cover STEP file on GitHub, cut the following shape out of a plastic sheet approximately ⅛ inches thick.

Step 43: Development Stand Assembly — 5

Build the stand as show in the images above and below.

Step 44: Development Stand Assembly — 5.1

Front view: Note the placement of all of the angle braces and plates. I suggest building from the bottom up.

Step 45: Development Stand Assembly — 5.2

Rear view.

Step 46: Development Stand Assembly — 5.3

This should give a better view of the orientation of the plate. Also note that there is a cross-bar underneath the metal plate. This is required for the leg to not bend the plate when jumping. This bar should be adjusted to be directly under the foot when the whole assembly is finished.

Step 47: Development Stand Assembly — 5.4

The above pictures show the connections at the top of the linear rail.

Step 48: Slide the Leg Over Your Finished Assembly

After completing the mechanical portion of your development stand you're now ready to slide the leg over fro the top.

Congratulations! You have finished the base mechanical assembly of the project! Now you’re ready to create the electronics and wire everything.

Step 49: Wiring the Motors and Encoders to the ODrive

The above visual wiring diagram shows all of the connections needed for wiring the motors and encoders to the ODrive.

While the project currently uses an original ODrive 3.5 mounted to the side of the hip, a custom single-motor motor controller based on the ODrive is coming very soon so that each controller can be built into the leg next to each motor. I’ve already finished debugging it I’m just working on optimizing the layout now. That being said, I encourage you to get yourself an ODrive, the ODrive is amazing and this project wouldn’t have been possible without it and it’s open source files.

If you’ve got a power supply or battery that will work already then you’re ready to start moving the leg! If not, continue to the power supply wiring guide.

Step 50: Wiring the Power Supplies

Parts needed for Power Supplies:

  • 2x Dell N750P-S0 Server Power Supply
    • I’ve bought 8 of these so far on eBay from various sellers, they go for around $25 to $30 for a pair of two!
  • About 10ft 14 AWG red wire or similar and About 10ft 14 AWG black wire or similar
    • This length is a guess I do not remember how much wire I used. This guess includes the length needed to get up to the leg.
  • 1x 8-circuit terminal block (4 Circuit is all you need for only two supplies)
    • This is used to connect the power supplies together in series. I wired 4 supplies to get 120A but I have never needed to try using more than 60 yet.
  • 8x Ring terminal crimps
    • These are for connecting the wires to the terminal block. Not necessary just nice to use.
  • 12x Female quick disconnect crimps, 16 - 14AWG fits well
    • These mate nicely with the power output terminals of the power supply (The blue crimps in the photo)
  • Some smaller wire, about 22-24 gauge is good
    • This is for connecting the pins that control the power supplies to the switches and E-stops.

Step 51: Getting to Know the Power Supply

The Dell N750P-S0 outputs 12V at up to 62.4A. We will wire two in series to get 24V. I have pulled about 40A from these power supplies, I cannot attest to how well they work when you approach their limit.

ATTENTION: These power supplies CANNOT be connected in series without modifying one of them. If you connect them unmodified, you will be shorting the 12V output on the lower side power supply to ground. This is because the output ground is connected to the input ground on each supply.

Step 52: Modifying the Power Supply — 1

Only the high side power supply should be modified. (The power supply for which it’s output ground will connect to the 12v output of the other).

To disconnect the output ground from the input ground, you will have to take apart the power supply.

Remove all of the screws on the outside of the supply shown above.

Step 53: Modifying the Power Supply — 2

Pull the top metal cover off of the supply as shown.

CAREFUL!!! There’s some large capacitors in here! If they’re charged they might be very dangerous! I suggest using a screwdriver or pliers to short the leads and make sure they are discharged. It’s the four large through-hole connections on the vertical board above.

When adjusting the voltage of mine I accidentally shorted one of the metal mosfet heatsinks to the outer case when it was powered on and it made a huge spark and left a brown burn mark on the heatsink.

Step 54: Modifying the Power Supply — 3

These two screws in the front are connecting the ground plane of the output to the outer case of the power supply.

You will need to remove them and replace them with nylon screws so that they do not conduct to the frame. I also put a few layers of electrical tape under the PCB to make sure nothing gets pressed together that shouldn’t.

Step 55: Modifying the Power Supply — 4

The nylon screws and electrical tape are shown above.

Step 56: Modifying the Power Supply — 5

Perform a test to see if you disconnected the grounds successfully

The multimeter should show no continuity between the output ground and metal case.

Step 57: Modifying the Power Supply — 6

You can turn the knob below to adjust the output voltage slightly as shown in the picture above. Use a multimeter to measure the output as you turn the potentiometer.

CAUTION!!! This step would require you to turn the power supply on while it is open. This is very dangerous and should absolutely only be done by experienced adults.

Step 58: Modifying the Power Supply — 7

All done modifying! Now close it back up and make sure to mark the outside of it to indicate that this one is the modified one.

Step 59: Wiring the Power Supply — 1

The picture and table above show all of the connections the power supply has, we will only be using the few bolded connections in the table.

Step 60: Wiring the Power Supply — 2

The picture above indicates which pins have to be connected on the power supply.

The pins in blue must all be connected together for the power supply output to be enabled. These should be connected through the on/off switch on the stand and the E-stops. (All switches should be in series so any one switch being disabled will turn off the power supplies)

The fan pwm control is optional. If you ground the pin the fans will not run, this will make it far quieter but the max current the power supplies can withstand before triggering a fault will be much lower. I did not use this pin.

Step 61: Wiring the Power Supply — 3

He're is a simple wiring diagram for the power supplies. The red and black wires should be about 12 to 16 gauge and the orange and blue wires can be much smaller such as 22 or 24 gauge.

Step 62: Checking the Output Voltage

Once you're power supplies are wired and you feel it is safe to test them, use a multimeter to ensure that the output voltage is in an acceptable range.

Secure the power supplies to the pegboard and connect some long wires from the power supplies to the leg once that's done you're ready to start making it move!

Congratulations! Great job getting to this point!

Step 63: Ready to Get Running!

Step 64: Going Forward

Now that you've got your leg and development stand fully built its time to start writing code for it! Check out the OpenLeg GitHub for example code. If you're interested in contributing or building more legs and assembling them into a walking robot feel free to reach out to me at openlegproject@gmail.com for feedback and advice.

Robotics Contest

Participated in the
Robotics Contest

Be the First to Share

    Recommendations

    • Instrument Contest

      Instrument Contest
    • Make it Glow Contest

      Make it Glow Contest
    • STEM Contest

      STEM Contest

    2 Discussions

    0
    None
    audreyobscura

    10 days ago

    What a cool project! which program did you model all of this in?

    1 reply