Warning: use this at your own risk. Stepper motors can get hot. Electricity is can be unforgiving. Please be careful.
**NEW*** Parametric openscad files now hosted on github:
Please fork, pull-requests welcome.
Basic Line follower/obstacle stopping code. https://github.com/lukewebdev/SMARS_Stepper_Line_Follower
Video of line following.
Video of drawing using SMARS dlc drawing attachment:
Sumo / bulldozer
Please "follow me" if you want to be aware of updates to this design or the future designs I am working on along these lines.
This is a variant of SMARS (listed in remix https://www.thingiverse.com/thing:2662828).
The STL print beds on this design contains (for convenience of getting the whole print bed) several SMARS components but the customized parts that are different from the original SMARS or new are as follows:
The Chassis (all new redesign especially axles...flat on top and bottom)
The Wheels (all new design, taller tread pyramids for wider-range of acceptable track tension, etc)
The track (simple y axis lengthening and oblong pin hole)
Samson Lock Pins - (these push between the two stepper motors to hold them in place)
The biggest single improvement in this design is the fact that all four wheels are mounted strongly on an axle, the motor shaft does not bear the weight of the vehicle. This means more consistent track tension and less issues with wheel wobble being more on one side than the other. No glue or anything is needed to attach the wheel and you can pop it on and off (carefully, and as few times as possible) using a tiny screw driver and prying on the slot below the chassis after removing the motors.
This variant uses 28BYJ-48 stepper (similar to the SMARS - 28BYJ-48 variant) but has a few important improvements over existing models:
- Wheel/track is now pretty fault tolerant across a range of print qualities and filament issues. Track tension is adjustable via quick-to-print custom size pins.
- 3 places to attach modules
- samson lock pins (from previous design)
- Has holders for the stepper driver boards.
- Has overhanging battery holders for 18650 batteries built into the design to eliminate 9v battery.
- Has an arduino uno slot but also another slot above it to stack a module there also.
- other holes for lock pins on each module attachment point for future expansion.
- Assemble two tracks, 16 track pieces each to make the tank tread. Use 1.75mm filament and use a soldering iron to mushroom one side to get the pins to stay in place. Do not make them permanently pinned in as you will need to remove some later.
- IMPORTANT: take a Q-tip cotton swab and swab petroleum jelly (Vaseline) inside the wheels and on outside of axles.
Mount the wheels with the track in place after removing all tree supports (careful, this takes force but don't break anything...be sure to look inside axle for tree support material you need to remove!)
Achieve ideal track tension by replacing as many track pins as needed, swapping the 1.7mm pin for a 1.9mm pin (or your custom size) to achieve the track tension you desire. Idea is to be loose so that it isn't pulling the wheel off center, but tight enough not to skip on the wheel.
If the wheel does not spin freely, use the spinner tool by mounting in drill using a pine wood derby mandrel mount or a screw or whatever you can put through the hole that is tight and will go into a power drill. Spin the slave wheel on each side (it will spin the master wheel due to track of course) on high speed for about 30 seconds...this will smooth and 'break in' the wheel so the stepper can move it easily. Let it cool down before deciding if it is broken in enough. DO NOT DO THIS WITHOUT VASELINE ON THE AXLE! It will immediately melt your whole axle/wheel assembly.
Test your stepper motors ability to spin the wheels by carefully mounting it (taking care to match shaft with inside of master wheel) using lock pins and basic 28BYJ-48 stepper code for arduino. Once they are for sure spinning easily in both directions, you can assemble the rest of the SMARS robot per the original SMARS instructions and common sense. See https://www.thingiverse.com/thing:3075289 for a photo of how to use the samson pins to lock in the stepper motors.
- If the stepper still cannot spin it, you need to break it in some more. If you have a bad printer or bad filament, your tracks might be too stiff and in this case, try printing thinner pins. Also use nyoil or some lightweight oil to reduce friction there however you can and run the drill some more. Obviously, do not run the drill spinner on a wheel that has a stepper mounted into the master wheel or it will destroy it. If your wheel is too tight and the track is not the issue, try the 'quick fix' under 'troubleshooting' section on this page.
To tighten the tension of your track, replace (as many as you need) several 1.75mm track pins with the 1.9mm pins (or other size of pin you can generate from SMARS_track_tensioner_pins.scad.)
Any questions, please comment.
More info on the track:
The track here has each mechanical piece enlarged on Y axis by 2%. It also has a much larger pin hole which requires melting one side of the pin to hold it in. The intention of this is to be able to make the track looser or tighter depending on how many 1.75mm track pins you swap out for thicker pins! Don't go thicker than 1.9mm or it will make the track stiff (1.9mm pins STL file is included).
It only takes 10 minutes to print enough various pin sizes to adjust your track (if needed) so for the adjustability this is a great trade off and beats remixing the chassis or wheels or tracks and reprinting those by a wide margin. See example here https://www.youtube.com/watch?v=J5IWcJb7sAs
The key with this build is to ensure you have eliminated as much friction as possible in the wheel so that a looser track does not skip as its first resort to actually spinning the slave wheel. See https://www.youtube.com/watch?v=qbcbW5KyKAs for explanation.
Also be sure you let it cool down fully after 'break in' spinning to test it. Do not spin it too much or you will overheat things and deform.
Don't use supports...chassis comes with tree supports which are more efficient than normal supports.
Please note: the print beds here are designed for a 200x200mm bed..if you need to move things around, please note that splitting the print bed STL will separate tree supports from the chassis! You won't get them aligned again so avoid moving the chassis. If you need to delete the chassis and tree supports and reimport it into your print setup then just use the separate chassis file included under files.
If your stepper will not spin the wheel....
If you've tried the vaseline and spinner tool, or do not have a drill for a spinner tool, and your wheel is too stiff for the stepper to spin it, try the trick in this video. Use a hair dryer or heat gun to soften the axle and pop your wheel on, then let it cool. It takes less than 20 seconds per axle and will work if nothing else does.