Howdy! Today I’ll be talking a little bit about my experience with the Sprout – part of the Runt Rovers line from Servo City. The Science Outreach club at my local community college recently designed an event around this kit, as part of a hands-on robotics demonstration! More about that later – first, I’d like to talk about the Sprout itself.
After opening up the package, I was impressed with the size of it. While the dimensions and reference photos are listed in the product description, actually opening it up and interacting with it really impressed me. There’s enough free real estate there to really do some interesting things! Combined with the standard Actobotics® hub pattern, it really makes for a versatile kit. Right away I also noticed that the plastic had a side with a sort of wood-grain texture that I hadn’t been able to notice in the photos. This pattern really makes the pieces feel like a more finished product, and give it a nice touch. I can see where this might not be for everybody, but not to fear! If you prefer a smooth surface, all the pieces can be flipped smooth side out for assembly.
There isn’t really a WRONG way to assemble the Sprout. The only thing I will say is that the plates which go inside the motors need to “point” downward (such that the hole tapers to the bottom). I’ve seen some kits work just fine with these placed the other way, but most often the inside of the motor won’t clear it. Now, just because there isn’t really a wrong way, doesn’t mean that there isn’t a harder or easier way. It’s tempting to place all of the plates and motors on the top, and then line up everything on the bottom and snap together. This can be a headache – many of these don’t want to fit nicely together all at once. If you watch the assembly video, you’ll notice that the motor plates have been attached to the bottom, while the motor and hub plates have been attached to the top. Attaching the top to the bottom in this configuration is MUCH easier, as you don’t have as much competition between things trying to line up. Just line up one hole at a time, then once they’re all lined up, snap them in one at a time. The snap lock for a controller, caster plate, and wheels are a cinch. I highly recommend the battery holder and adapter as well, provided you’re using AAs. The battery compartment can be fairly easily removed to replace batteries when needed – you don’t need to disassemble any of the rover to do so. (In the picture you can see that there is room to just slide the battery tray through the side of the assembled rover.)
For our purposes, we hoped to make kits which were also reusable. The Sprout does pretty nicely in this regard as well. A word of caution though – excessive force on the prongs when trying to push them back out WILL snap them. If you use pliers to squeeze them back through, only apply the absolute minimum of force needed and you shouldn’t have a problem. Once the Sprout was together, I must say I was again impressed with how sturdy it seemed to be. For a snap-together plastic kit, there’s not a lot of flex, and no wobble. Not that it would really need to, but I imagine it could take some punishment!
For our kits I chose a picaxe microcontroller. When I was first starting out, I found programming them to be very intuitive and approachable, and I wanted any students working with programming the kits to have that same experience. To minimize costs, I chose a picaxe 18M2 with an 18-pin High Power Project board. The latter is sadly now discontinued, but there are plenty of other picaxe setups which could do the job. Dropped the PIC chip and a motor driver into the IC sockets, soldered in the needed pins, and used squares of cardstock to color code them to the jumper wires used for the components. If the wire ended in a green wire, it goes onto the green square, blue onto blue, etc. Altogether there were 4 pins for the sensor, 4 for the motors, and two for the power. (The two pictures below show the pin labels, and then the hooked up result.)
I additionally labeled the motors so that they wouldn’t accidentally get hooked up backwards.
This was all done to make it as user friendly and easy as possible, while still reaching the same end result of an autonomous mobile robot. The idea was to demonstrate how POSSIBLE these things can be, especially to kids in a rural area who don’t get a lot of opportunities for this sort of hands-on experience.
To grant our kit autonomy, our Sprouts needed to sense the world around them. For this we used some SR04 ultrasonic sensors. I glued these to some short craft sticks to give them a mounting point, and attached some heavy duty locking strips to the bottom (think Velcro, but overkill.) These are fairly accurate and easy to work with, while being VERY cheap. Admittedly, it’s sometimes best to get a couple extra of these, as they are sometimes duds.
Now the adapter and battery tray were meant for 4 AAs, but our kit called for 3. To fix this, I just jumped the last contacts of each tray with some heavy wire.
In order to tell assembled kits apart, I also cut down some cheap paint brushes so that they slid snugly into the holes at the back and front of the Sprout. After removing the bristles, I fashioned little flags that slid in so students could use to personalize and identify their bots.
I tested each set of boards and components, labeling each, and we were good to go!
Now, unfortunately a backorder from one of the suppliers (not Servo City) had pushed back our ready date. This meant that the end of our semester was almost upon us. We tried to contact several schools, but none were able to make it out in time. In order to still have an event this semester, we instead did it as an open house and invited the campus. While we didn’t get a huge turnout, we still had fun, and hopefully spread interest in robotics!
Our experience using the Sprout rovers, specifically, could not have been more positive. The Runt Rovers seem to be a great educational opportunity, for budding roboticists of any age. Here is a video of one of our kits in action.
For anyone interested, here’s the code running on them.
Jeremy Walker has been in the process of setting up a mobile robotics outreach lab through his community college to help build STEM interest for students in the local area.