Introduction: Trackbot Mk V
I wanted to replace my old radio controlled robot that I've taken to past Maker Faires (https://makershare.com/projects/robot-driver-license). I've shifted away from Vex parts to Servo City Actobotics parts - they're lighter and more versatile. This was a fresh design from the ground up. Also gave me the opportunity to exercise new skills - powder coating and cutting sheet metal.
Note- updated Aug 5 2018 with different motors
Step 1: Materials
- Actobotics 10.5" Channel (2)
- Actobotics 6" Channel (2)
- Actobotic Pattern Plate 4.5" x 6"
- Actobotics 6-32 Thread, 1/4" OD Round Aluminum Standoffs
- 0.25" (8) (for mounting plates)
- 0.5" (1) (for battery holder)
- 0.625" (1) (for Wago 3-hole nut)
- 0.875" (2) (for nylon bushings)
- 1.0" (1) (for Wago 5-hole nut)
- 1.32" (4) to stiffen channel at axle points
- 2.5" (1) (for RC receiver holder)
- Lynxmotion Modular Track System (MTS) 2" wide track (need 29 links x 2 - need to order 3 tracks of 21 links to have enough)
- Lynxmotion MTS 12T Sprocket (6mm Hub) (4)
- Servo City 98 RPM Economy Gear Motor(2)
(Note: originally used 195 RPM premium planetary gear motors but they didn't really have enough torque to spin in place, then I tried the 52 RPM premium planetary gear motors. Torque was better, but considerably slower. I settled on these for more speed and even better torque)
- Actobotics Gear Motor Input Board C (2)
- Actobotics Aluminum Motor Mount F (2)
- Actobotics Set Screw Shaft Couplers 0.250” to 4mm (2)
- Actobotics 0.250" (1/4") x 3.00" Stainless Steel D-Shafting (2)
- Actobotics 0.250" (1/4") x 2.00" Stainless Steel D-Shafting (2)
- Actobotics 1/4" ID x 1/2" OD Flanged Ball Bearing (6)
- Actobotics Aluminum Set Screw Collars 0.25" (6)
- Actobotics Shafting and Tubing Spacers 0.25" (10)
- Lynxmotion nylon bushings (length cut to size - just under 7/8") (2)
- see https://www.instructables.com/id/Robotics-Claw-Mo...
- Note: I upgraded this several years ago to 7V tolerant servos. Main servo is Hitec HW-5685MH. Not sure what the micro-servo is -- I can't read label. Pretty sure it's a Hitec
- RoboClaw 2x7 Motor Controller (from Servo City)
- DFRobot Romeo v2.2 microcontroller
- 3D-printed Romeo mounting plate (https://www.thingiverse.com/thing:1377159)
- Stepdown Buck voltage converter (Amazon https://www.amazon.com/gp/product/B00VWL41TM)
- Wago Lever nuts (from Amazon)
- Red-black wire (from ) (from PowerWerx.com)
- Anderson Power Poles (from PowerWerx.com)
- DPST Heavy Duty Latching Toggle Switch (from Servo City)
- Turnigy Nano-tech 3.3 3300 mAh 3S LiPo battery (11.1v) (from Hobby King)
- 3D-printed RC Holder (https://www.thingiverse.com/thing:2779003)
Step 2: Basic Frame
The first picture is actually the bottom. Make a square frame with the Actobotics channel. Note that the back channel is not at the very back, to allow room for the motors. Also note that it has the open part facing what will be up on the robot- the battery will go here. Brackets are added for the bottom plate and top pattern plate.
Actobotics channel and other pieces were powder coated at TechShop St. Louis (before it folded).
Step 3: Motors and Sprockets
The hubs on the sprockets were 6mm. I had to drill them out to fit the 0.25" axles. I used flanged ball bearings to support the axles. The powder coating on the frame actually made the fit too tight, so I had to file it away. I used spacers to keep the set screw collars (1 each) and track hubs (2 each) from interfering with the ball bearings.
End cap bumpers were 3D printed. Held in place by single machine screw; single screw plate glued into place in the printed end-cap.
Step 4: Mounting Claw
The small piece was cut from 0.125" aluminum to fill the gap in the claw base (where a servo could go - see https://www.instructables.com/id/Robotics-Claw-Mounting-Bracket/). I also cut from thinner (0.063") aluminum top and bottom plates. The top plate was powder coated to match the frame. The bottom plate was cut to fit inside the channel. I marked where the holes needed to be with a fine marker and then drilled with drill press. As you can see alignment wasn't perfect - had to extend a couple of holes with a file. With 5 screws the claw is very firmly mounted.
Step 5: Mounting Electronics
Electronics were mounted to a 4.5" x 6" plate, which in turn was mounted to brackets on the frame.
Romeo board was mounted on a 3D printed mount.
Motor controller was mounted onto a custom-cut plate (0.0375 aluminum - powder coated). Slits were cut to roughly match where the mount that came with the motor controller were located. They're a bit sloppy (cut with cutting wheel on Dremel), but no one will see it where it's mounted. The motor controller was raised a bit on 0.25" stand-offs to allow some airflow underneath.
I've started using Wago lever nuts for power distribution. I used standoffs with a washer on top to keep the pair of lever-nuts from slipping down when robot right-side up. Just a zip-tie to fasten pair of nuts to stand-off. The shape of the nuts give a nice v-groove when a pair are stuck together with double-sided tape.
I don't really like the display on the buck stepdown converter (wastes electricity), but I wanted to be sure I had one that could handle enough current for the Romeo board and the servos. The converter steps the 11.1V from the battery to 7V for board and for servos (one thing I like about the Romeo is that it has separate power input avialble for servos). It's on a 0.019 aluminum plate cut to fit available space.
Wiring is routed through the channel, and up through holes in mounting plate for Romeo and motor controller. I wired in a simple toggle switch for on/off control.
Battery compartment is just he frame channel mounted open-side up. I put in a piece of neoprene foam as a shock-absorber. It's just hot-glued in. Battery is held in place with a small beam bracket on top of a standoff.
RC receiver was 3D printed and then mounted on top of standoff. I made my own wiring mounts, but you could just use regular wires with female ends..
Step 6: Bottom Plate
Bottom plate was cut from 0.0375" aluminum. It's designed to protect "insides" of robot. Installed on mounts attached to bottom of frame (see photos in frame section). Nothing is mounted on bottom plate. The plate needs to be attached before the tracks are put on.
Step 7: Track
I added nylon bushings over standoffs to take up tension in the tracks - the spacing was empiric. Lynxmotion track was assembled except for last link, then put on sprockets in the middle of the track.
Step 8: Final Comments
Overall robot works fine. The newest motor is a reasonable compromise between speed and torque. A fun project overall.