Tracker SkidSteer: Tank Track version evolution

Update July 29 '24: I now have a custom PCB that is open sourced. Gerber files available at: https://github.com/crabbedh/RC_Controller You are free to have PCBs made for NONCOMMERCIAL (ie: NOT TO SELL) use. This PCB fits in this Track version of the mini-skidi and in the large Mini-Dump model.

Update: June 14 '24: Have you lowered your arm into your tracks and heard the “CRACK” as gear teeth break, either in plastic, or in your arm motor? I now have a fix for limiting the travel of lowering the arm. See ARM/BUCKET MODS section & video below.

Update: June 6 '24: Release of a dual joystick control for tank treads. “Tracker2Joy”. Lots of comments in code. You will likely need to change some values in the first section to match the wiring of your model. Should support wheel & track version, all Prof Boots versions and my remixes.

Update: June 6 '24: NOTE: The EspressIF board manager 3.x.x (just released at time of this writing)  for ESP32 (used in the Arduino IDE) is not compatible with the ESP32Servo.h library used in all code for SKIDI that uses this library (all code here). You must downgrade to the last 2.x.x version of the EspressIF board manager at this time.

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This is an evolution of the V2 and V3 versions of the Mini-Skidi design by Professor Boots. This design only supports  tank-tread locomotion and uses the PS3 Controller. The major difference in this design is the use of bearings at all 4 ‘wheel’ locations; but there are many “tweaks” to parts that I've found helpful as I build additional versions. The bearings and redesign of the motor-hub interface, along with a 4mm narrower tread, was designed to reduce the friction of the tread drive train and permit a bit more consistent motion when using a proportional throttle for speed control. All design changes are illustrated here and in the notes contained in the files section. I also include PS3 Controller Arduino IDE code that supports proportional control, digital control (full speed or off), and a light system.  There are one joystick and two joystick versions of the software that control the tank treads.

My thanks to Professor Boots for making his Skidi designs available for others to use. He also provided great workshops for many other design models at very reasonable prices. His site is at: https://professorboots.com. He has a Discord service for all his designs with lots of help for builds. Search for ProfBoots on Discord.

This model is designed for the DIYers who source all parts themselves and want to play around with extending the boundaries of the PB original Skid Steer and experiment with features such as proportional throttle control, LEDs and other motor options; such as the use of N30 motors.

The drive train uses two bearings. For the non-motor side, the drive shaft is a simple M5 screw that goes thru a bearing with a 5mm opening and onto the hub. The hub is now very solidly supported and spins freely. At the motor end, pushing the motor to the housing wall allows that track hub to connect directly to the motor shaft. *** you must use motors with 10mm shaft ***.  There is a grub screw on this hub to help ensure the hub is solidly fastened to the motor shaft. Finally the tensioner support has a larger base for supporting the downward force of the track. The track itself has a little thicker support between the track plates which makes it a tad easier to print. The track is also 4mm narrower. With all these changes, I think the rolling resistance has decreased and is more consistent which allows a proportional throttle to drive the Skidi straight, even at slow speeds.

For those of you with Version 2 of the Professor Boots' Mini Skidi PCB, I have included a document that shows how to modify the PCB to allow you to run all motors directly from the 2S battery for about 40% more power and speed!

Here is an overview of the design from YouTube:

Print instructions:

Most parts are printed in PLA with 3 perimeters and top/bottom walls at 0.2mm layer height. I use PETG for gears, LED holders, cable clip; TPU for the track and CLAW-BUCKET ROD. 

All parts in the STL section were modified from the original Professor Boots design. However, many of the original parts are fully compatible.

Most of the hardware required

• Drive Motors:  2 x N20 motors: 12v@100rpm to 150rpm. (I tend to use 140-150rpm) N30 drive motors are possible, but not yet tested as they are on order. 
• Arm (Lift) motor:  1 x N30 12v@30rpm or N20 6v@15rpm or 6v@10rpm with 12mm gear section (Horserace Store on AliExpress). Others have used N20 12v 60-100rpm but I think they often use the 3rd gear, which my housing does not support. You may find your particular 12v@30-100rpm works fine for the arm.
• 2 x M5 x 16-20 screw-button head with M5 lock nut
• bearings:  2x 5x11x4.  and 2x 3x7x3. (RS or ZZ)
  683RS(10) & MM115RS(10) FUSHI OFFICIAL Store (Aliexpress) for $20/Cdn mine came within 2 weeks (Canada)
• various M2, M3 screws
• header strip for the servo connection and socket strip for DRV8833, Regulator and ESP32 (optional). 
• LiPo battery (V2 PCB) or 2 x Fenix ARB-L16 USBC rechargeable (v3 PCB). For the LiPo I am using the 450 and 550mAh Tattu versions.
• Bucket & Claw: 2 x MG90S Metal servos (claw is optional)
• PCB (can send Gerber files to JCLPCB.COM to get 5 built and shipped for under $10)
• ESP32, DRV8833 motor driver and regulator and other parts as shown in picture at top. The electronic parts must be exactly as shown or else the code may not work properly. ESP32 (30 pin) is available from Win Win Store, AliEx. 

Drive Train

You will need 5x11x4 (2) and 3x7x3 (2) bearings along with  M5x16 button head screws (2) and  M5 lock nuts (2). The instructions for installing the motor hubs and the no-motor hubs are contained in the zip file in the OTHER FILES section. You will also need to drill out the no-motor holes in the housing to 5mm (get a 5mm drill bit). You cannot make a vertical hole exact so it is undersized and intended to be drilled to get a better fit. (use 3 perimeters on housing). You may also need to do this to the hub if your M5 screw does not slide easy thru it.

Test your printer for bearings

Since every printer extrudes differently, I've provided a folder called TEST WALLS where you can print just the wall section to ensure your bearing fits tightly. If not, you can adjust the hole sizes for your particular printer. I've provided the STEP file for the housing. The ‘peaks’ at the top and bottom of holes are intended and assist when printing vertical holes accurately.

Motor Support

Using standard N20 12v@100rpm motors will work fine. If you wish to use the proportional throttle, I find slightly faster motors better: N20 12v@140 to 160rpm. This gives a wider range of useful speeds. The drive motor sections should support N30 motors, although I have not installed N30 motors there yet, as they are on order. 

From the pictures, you'll notice 3 motor sizes. For lifting the arm, I have found that many of the standard N20 motors from AliExpress (with 9mm gear section) do not have enough torque to lift the bucket, claw and metal servos. To aid in this, Professor Boots has included a 3rd gear in the arm section. Instead of this solution, I tend to use the middle motor (shown in the picture) that has a 12mm gear section and supports speeds of 6v@15rpm, or 12v@30rpm. This motor is difficult to obtain as many AliExpress stores will send a motor with this speed, but use the 9mm shorter gear section which doesn't provide enough torque. (I suspect they are using a slower, weaker motor in the first stage) The 12mm proper motors are available from Horserace Store on AliExpress and a few others. As an alternative, I've used an N30 motor in the arm with great success. The N30 will just fit, but you must ensure your solder joints on the back of the motors do not make the motor longer.

Note: If you use the 1:1000 6v@15rpm motor, one gear extends beyond the gear box by 0.3mm and could bind when covered. There is a small cutout in the arm motor mount and cover to prevent binding with this motor. There is no potential problem if you use an N30 arm motor.

Lights

In the OTHER FILES section, I show how I've used the single AUX MOTOR control for both a forward-facing LED bar and a top mounted flasher. When backing up, the LED in the red flasher will flash and the LED bar is kept off. When not backing up, you can turn the LED bar on/off by pressing down the right joystick. You don’t need to build both, you could just build one of the two and the code should work fine. 

Screws

Because I have a large inventory of metric screws, I've used M2, M2.5 and M3 machine screws in this design. But the original ‘wood-screw’ type used in the PB kits should also work fine. You may need to drill out a few holes so it is good to have a 2, 2.5, 3 & 5 mm drill bits handy. You will find that slightly longer or shorter screws than I've used will also do the job.

PCB support

The housing supports the V2 Skidi PCB from Professor Boots and available on GitHub. You can zip (use a zip format not just a bunch of files) all the Gerber files and go to an on-line PCB manufacturer and upload. JLCPCB.COM is the one I’ve used and it is a very easy process to order 5 boards for about $5-7 USD. You may need to use a dropdown to select a very cheap global shipping option, but it is there.

There is a DISCORD server for ProfBoots that will list where to get various electronic parts.

The V2 PCB provides 5v to all motors. A simple mod can route the full 2S battery (8v) to all motor driver outputs which greatly reduces the load on the regulator and provides more power to your motors. Details are in the OTHER FILES section.

Note that in the V2 PCB, I tend to solder the ESP32 directly to the PCB without using sockets. This gives more room for my LiPo battery. **THIS IS A RISK*** . Because if you do something to kill your ESP32, you likely need to build up a new PCB. I have several V2 PCBs and lots of Skidi parts.. so while this saves space and allows me to use a LIPO easily, be aware of the trade-off.I have built 4 Skidis like this and they are all going strong for 6 months.

The housing is designed to also support the V3 PCB, but I have not tested that feature yet.

Motor Connections

You'll notice, if you watch the video above, that I've not used any screw connectors on my PCB. I purchased 2 pin JST connectors (2.54mm version) that had leads and cut them appropriately and soldered the males to the PCB and the females to the motors/LED system. These allow me to quickly remove a motor or disconnect the LEDs on the top when servicing. Not sure if this is better, yet. 

Servos

Note on Servos: Servos need to reach the position demanded by the input signal. If they can't, because of obstruction (they might be squeezing an object), the servo powers its internal motor continuously. But since the motor can't rotate further, a high “stall” current is induced and, if left in this position, will cause the windings to heat up and the motor will eventually burn out. I printed the Claw Rod part with 100% solid TPU to allow it to stretch. If the claw squeezes an object, the TPU claw rod will stretch and allow the servo horn to reach its desired position and the motor will stop. But the TPU rod stretches and exerts a bit of squeezing force against the object. This prevents the servo motor from overheating with an additional benefit of giving some gripping force for squeezing objects. 

 Arm/Bucket Mods

I've made a few mods to limit damage to the arm. I've usually damaged the arm by mistakenly lowering the arm into the track. Hearing a “SNAP” means I've broken a gear tooth in the pinion, large gear, or in the brass motor gear section. The video below shows a solution to easing the burden on the arm. STLs for 3 versions of the large gear are included in the model files. The one I use for my model here is indicated, but you might need the 2 tooth flat area moved one way or the other, so I provided those options.

Arm motor used: N20 12v30rpm (or 20rpm) from Horserace Store - AliExpress: Must use a 12mm gear section.  Now you can also use an N30 12v30-50 rpm as well. I have found the N30s have more torque and will fit in my housing if you solder the wires just right.

Metal pinion: M0.8 hardened steel 10T pinion (3.1mm hole) with grub screw from Shaluoman Store - AliExpress: This is strictly optional, the plastic pinion works fine in PETG.

Trailering!

With the narrower track, I discovered that Tracker will fit on the first iteration of Professor Boots trailer. I can now transport to the next job site!

Evolution

The STLs and features will evolve and I'll post updates from time to time. If you need a particular STEP file, let me know and I'll post it.

Code

The software included in the files below uses specific board and libraries and might not compile if yours are newer. You can install older versions in the Arduino IDE. Select the ESP32 Devkit V1 board and I use the following board manager: ESP32 by Espressif System V2.0.17. Then ESP32Servo: version 1.2.1 and PS3 Controller Host (Pernis) V1.1.0. 

v1.0 of Tracker code for Arduino IDE is now below.  There are now two, count'em, two, versions of software. In the first, your left joystick controls all locomotion and turning. In the second, The left joystick controls the left tread and the right joystick controls the right. Both versions of software can provide proportional or digital throttle control and both can support LED headlights (or light-bar) and/or a top-mounted LED backup flasher. You simply change two variables from false to true to enable these features. 

A video that walks thru how the code works is below and features the state of the first version of the code at the time the video was created. It will evolve:

• bearings used on all drive motors and wheels
• narrower track to reduce friction
• arm gear mod to prevent damage to arm when lowering bucket into tracks.
• support for N30 arm motor (& possibly all drive motors)
• flasher & LED bar feature
• Mod of Prof Boots V2 PCB for increased power to motors
• tweaked claw hinge to reduce load on claw servo (use TPU)
• housing supports V2 and V3 PCB
• code mod to support proportional throttle
• you can add mini-13 figure for fun!