the Mini-Skidi Rubber Remix

This is based on the excellent design work of ProfessorBoots who created the RC controlled Mini-Skidi, using a wifi-enabled ESP32. His original work is here: https://www.instructables.com/3D-Printed-RC-SkidSteer-V20/

The Rubber Remix was created to support the use of easy-to-get soft rubber/silicon tires and it solved a drive-train problem I was having. The specific tires used in this remix are shown in the two videos below and readily available from several stores on AliExpress (and likely other places). Since then, I've added a number of improvements to the fit and strength of connections. I've also modified the bucket slightly (to prevent the teeth from getting caught under objects) and make the forklift narrower to support lifting all edges of a smaller pallet.

I added a ‘backup flasher’ to the top of the cage and a 2S LiPo battery monitor feature. 

The code for stopping the arm was modified to ‘brake’ instead of coast. If you find your arm drops to the ground when you try to stop it in mid-air, you may wish to look at this mod. 

There is an assembly PDF file in OTHER FILES that details basic assembly changes for the parts modified here.

The video below shows some of the earlier modifications but might not reflect the current state of all parts.

Update Oct 26, '23
Modified release code to control all N20 MOTORS with PWM. Also includes 3 other mods of a) arm-braking b) up/down buttons c) better slider position on boot. skidiBrakeV2PWM.ZIP

Update Oct 7, '23
I added a document that explains how to ‘brake’ the arm motor. If you find that your arm drops all the way to the ground, when you intend it to stop in mid-air, read the PDF in the OTHER FILES section to explain how to fix this.

I also modified the released code (Oct -23) to BRAKE the arm motor, and to replace the arrow buttons on the arm motor so they show UP/DOWN. The released code is in OTHER FILES and called “skidiBrake.zip”. 

Update Oct 6, '23
Modified the forklift so it works with all edges of a slightly smaller pallet. I found with the mods, my smaller pallet can have slightly heavier loads without tipping over the Skidi. I've included STL of both. These work well with the Warehouse model by Wim V. I'm added some enhancements to make it Skidi-Proof at: https://www.printables.com/model/603496-a-skidi-proof-warehouse

Update Oct 4, '23
My arm motor restraint was not tight enough to keep the arm motor from slipping sideways under the clamp and disengaging the arm gear, so I added some alignment strips to hold it tighter. armMotorRestraint.stl is the new part. Now unfortunately, this only works for 6v@15 rpm motor, which might not come with the kits. I prefer the 15rpm motors for their strength and smoothness. These have different physical dimensions in the gearing section that clamps under the support and so this support is custom designed for the 15rpm model. I've added the STEP file so you can mod for faster motors. When installing, do not orient gears so they rub against the plastic.

Update Sept 19, '23
I've added V2 to many parts. These have increased the depth of the square connection between the pulleys & wheel hubs; and between the arm gear and the left arm. The arm gears have wider teeth to make them stronger when they mesh. (Print top part of arm gear at 0.1mm layer height) The fender provides more clearance for the large rubber tire.

Update Sept 17, '23:
I have found that the teeth of the bucket get caught if you use a backstop to push an item into, so that you can lift it up. I've modified the bucket so that the teeth can no longer go under such a backstop. This will prevent the bucket servo and/or the lifting arm motor to overload. See the pictures at top for a comparison image. This bucket has the same mounting holes to support the original claw. V2 now supports a metal gear servo which has 2mm longer body than plastic.

Update: Sept 16, '23:  
I've added a battery monitoring feature to my SKIDIs. Although no 3D printed parts are required, I have added a PDF file that describes the hardware and software that provide this feature. I currently use both the built-in LED on the CPU and the flasher on the cage roof to provide a battery status indicator (1 to 5 flashes) and to provide status when the battery is too low and must be recharged. NOW at V2.

Update: Sept 11, '23:  
Added a red LED flasher to the top of the cage. See below for details

Update: Sept 10, '23:  
Some builders had their right arm pivot break on the original model. I've never had that issue, but added the extra pivot support on the right arm, and modified the housing to accept the slightly larger diameter pivot of the right arm.

I also added support for a smaller (38mm) rubber wheel that does not require the longer arms or higher fender. (although the longer arms do allow a wider range of articulation of the bucket). See video below.

Update: Aug 30, '23:  
I've added a universal pulley with a bit wider shaft hole. Some complained they damaged their N20 motor trying to install the original. This is caused by the printer over-extruding slightly and the hole being too small. The ‘wide’ universal pulley increases the shaft from 3.15mm to 3.35mm. 

************************************************************************************

If you want to use the larger rubber tires, you will need to use the longer arms and the higher fenders. A smaller rubber wheel, (see pictures for ordering info and video below) has less grip than the large rubber tire, but  more than TPU. It turns without any ‘hopping’ and is a pretty good compromise between TPU and the very grippy larger wheel. However, the large wheel is much more of an ‘off-road’ beast! The longer arms also work well with the smaller rubber wheels.

The video below shows the 2 different tires and their performance, as well as the operation of the arm with motors of different RPM options. It also demonstrates the ‘braking’ feature of the H-Bridge motor drivers. A larger battery holder is also demonstrated.

This remix uses a single “universal” pulley or drive shaft on all wheels, and is designed for the housing included. The pulley here was designed to provide enhanced meshing of the TPU belt. The first released designs would tend to wander off the pulley, but I think that is now much improved.

The new arms  are only necessary to provide clearance for the new larger tires. (but work well with the smaller tires)

The cover and cage are optional, and now mount using a flathead M3 x 10 screw on each side. The cover has a handle for easier opening and my logo (I couldn't resist).

Here is a video to help those who may struggle getting leads on those N20 motors or getting the belt drive train parts installed. This was NOT shown using my remixed housing with the belt guides as I didn't have an extra printed at the time. With my housing, the belt stays aligned better, but it also gets snagged on the guide post as you insert the motor, and you'll need a small bent tweezer to pull the belt up and around the guide post so it sits against the housing wall as you lower the motor into its support.

Flasher update: I added support for mounting a flashing LED to the roof of the cage. I used a 5mm flashing red LED (red lense). I designed a flasher housing using transparent filament. Print with only 1 perimeter so the bridging does not droop. (0.2layer 5walls top/bottom) There are 2 versions of the cage. One has a 10mm hole on top for inserting the flasher housing and gluing it to the cage. (glue the flange of the housing to the underside of the cage). You will need to solder a 220-330 (220 slightly brighter) ohm resistor to one leg of the LED. (see picture above for assembly guideline). You'll then connect to a 3 pin connector. (Do not use the middle pin). Currently you can only attach this to the location where the servo claw plugs in. the anode of the LED should attach to the top of the terminal block and will go to the ESP32 pin D22. The cathode of the LED goes to the GND input. (One end of the LED to the top of the connector, the other pin to the bottom). Although there are 3 other ‘ports’ on the terminal block, none go to an output port that is suitable for use. You can cut a PCB trace and wire one of the unused 3 terminal connections to D2 or D4 for use and I'll provide info on that later. Use heat shrink tubing after attaching the LED and connector.. A 3-pin female Dupont connector is best (if you have a broken servo, cut off the connector). For now, I leave you to modify your code; but simply set the pinMode(22, OUTPUT). I use the flasher only when backing up, so in the backup CASE statement, do a digitalWrite to the flasher with a HIGH (or 1).  digitalWrite(22,HIGH); Just before the CASE statement, write a LOW (or 0) to the flasher so that it is turned off, unless it is backing up. You'll need to bend the LED pins near the underside of the cage towards the terminal block as the PCB will likely interfere if you leave the pins straight down. V2 of the flasher case is slightly shorter and tighter. A video of the flasher in operation is here: 

Parts that I did not change are found in the original project.

Some STEP files are included. Please feel free to contact me if you wish other STEP files.