I estimate that I'm about halfway through my first winter in Buffalo. And in this weather, I'm always on the lookout for RC gadgets that can thrive in the snow. My latest project began life as a toy-grade RC vehicle with a dubious reputation, but a few simple modifications turned it into a super snow machine. More-extensive tweaking made it even better!
The Terrain Twister is an RC toy that was previously sold by Mattel under both the Hot Wheels and Tyco RC labels. It's discontinued now, but new and used examples are readily available on the internet. What caught my attention is the Twister's really unique screw propulsion system. Rather than wheels or tank treads, this vehicle is motivated by a pair of counter-rotating cylindrical pontoons that have external threads like a screw.
There have been a few examples of screw-propelled vehicles throughout history. The buoyancy of the rotating pontoons allows them to move across swampy or muddy terrain that would cause wheeled or tracked vehicles to get hopelessly stuck. Screw-propelled vehicles also excel in the snow.
Online reviews of the Terrain Twister are all over the map. Some people love them, and lots of people despise them. A cursory analysis hinted that many of the haters had tried using the Terrain Twister on surfaces that it wasn't meant for. Spoiler: a screw-propelled toy is NOT going to work well on your concrete driveway or the tile floor of your kitchen. I eagerly pulled the trigger on a used unit I found on eBay…a whopping $5 investment (+$9 for shipping)!
My Twister included the actual vehicle and the control transmitter. It did not include the proprietary battery or 5-hour charger. That suited me just fine since I planned to use LiPo batteries anyway, and who the heck wants to wait 5 hours to play with their RC toy?
The proprietary battery is a 6-cell, 7.2-volt NiMH unit of unstated capacity. Hinges on the battery allow it to bend to fit the unusual stepped battery compartment of the Twister. A fully-charged 6-cell NiMH battery has a voltage of about 8.4 volts, which is also the charged voltage of a 2-cell LiPo battery. Perfect! I found a few different 2-cell LiPo packs in my stash that physically fit into the battery compartment.
Metal electrical contacts in the battery compartment engage with mating contacts on the stock battery when it is installed. My LiPo batteries obviously had no such contacts. They use hobby-grade plugs. I simply soldered a pigtail with a Deans Ultra Plug to the vehicle contacts. There are even marks on the plastic body that indicate the polarity of each contact. I made sure to solder quickly to avoid melting the plastic around the contacts and stinking up my shop!
Swapping batteries was my only initial change to the Terrain Twister. Input voltage was the same and I retained all of the stock onboard electronics. Perhaps the only delta affecting performance was the weight savings of my LiPo battery over the stock unit. I would guess that the 2S-700mAh LiPo I chose shaved three or four ounces off of the original weight.
The transmitter uses a standard 9-volt battery. For some reason, 9-volt batteries disappear around my house. That's okay because I found that most 9-volt devices work just fine with a 2-cell LiPo. Several of my seldom-used 9-volt electronic tools (ex: stud finder, tachometer) have been fitted with hobby-grade battery connectors. When I need to use one of those tools, I just connect a small 2-cell LiPo. I made the same modification to the Terrain Twister transmitter.
Once again, I soldered a pigtail to the contacts in the battery compartment. I used a Deans Micro Plug since that is the connector on the battery I planned to use. The 300mAh LiPo doesn't fit inside the battery compartment. So, I added self-adhesive Velcro to the back of the transmitter to hold the battery during use.
With the simple addition of those two battery leads, my Terrain Twister was ready for testing. A quick check in my workshop confirmed that everything was operational. My next move was to head outside.
Using the Stock Radio
The weather was a little above freezing that day. All of the snow in my back yard had condensed into a smooth dense blanket. I soon found that conditions were ideal for driving the Terrain Twister. The little machine plowed its way over the snow with surprising authority. It did great on flat areas and was even able to climb snow drifts. The Terrain Twister may be a toy-grade machine, but I was having serious fun with it!
A joystick on the left side of the transmitter controls the spinning motion of the pontoons. Pushing the stick forward commands both pontoons to rotate for forward motion. Moving to the top left corner causes the left pontoon to stop while the right pontoon moves forward. This results in a left turn. With the stick directly left, both pontoons rotate counter-clockwise, which makes the Twister crab to the left. The same control methodology applies to all four quadrants of the joystick's range of motion.
On the right side of the transmitter is a 3-position, spring-loaded toggle switch. In the default, center position, the pontoons are parallel to each other as viewed from above. The upper switch position commands the front of the pontoons closer together and separates them at the rear. Moving to the bottom position has the opposite effect. This movement allows some degree of turning ability while using the crabbing motion.
While the control methods are intuitive and effective, there are limitations. The biggest problem I found is that the motor speeds are not proportional. A pontoon will spin either full forward, full reverse, or not at all. This made control response a bit choppy and harsh.
I also thought that the function of the right switch wasn't very useful…especially on snow. I didn't do much crabbing to begin with and didn't need to turn those times when I did crab. As a result, I rarely used the switch.
While I was having fun with the mostly stock Terrain Twister, I thought that the deficiencies of the controls could be easily overcome by installing a hobby grade radio system. However, I had one more test before ripping out the stock electronics. I found a YouTube video that mentioned using a 3-cell LiPo (12.6 volts when charged) in a Terrain Twister. I wouldn't normally consider such a significant voltage boost with mystery toy-grade electronics. But I had nothing to lose here since I was gutting the model anyway.
I popped in a 3-cell 850mAh LiPo and had several more minutes of fun with the Twister. The extra voltage provided a significant jump in top speed and didn't seem to create any adverse effects. I'm sure that the cold weather helped the circuit board deal with the extra volts and amps, but it never let out any magic smoke.
If you just want a quick and easy upgrade on a Terrain Twister, keep the stock electronics and throw in a 3-cell LiPo. My experience suggests that there could be enough headroom to handle the performance boost over the long haul. Then again, maybe it will self-destruct…it's hard to say with certainty. Choose your level of risk. As with any project that inserts a LiPo in place of a NiCad/NiMH battery, I suggest that you also use a cheap plug-in voltage alarm to prevent over-discharge.
My first step in the radio overhaul was to remove the top of the Twister's body. Most of the screws are easy to see. But it took me a few minutes to figure out that four screws in the center of the body are hidden under stickers.
I needed to identify the wires attached to the drive motor within each pontoon and remove everything else. The motor wires were easy to spot since they are the only wires routed into the pontoons. I desoldered these wires from the exposed circuit board inside the main body.
After that, I just went from front to back removing all of the stock electronics. The radio gear is housed in a sealed container near the front. I pulled the whole container in one piece.
The mechanism for changing the pontoon angles is very clever. It is also heavy and complex. An electric motor turns a jackscrew through a series of gears and causes the pontoons to rotate in unison.
My experience with the stock set-up convinced me that I didn't care about being able to change the pontoon angles. I removed the control motor, but left the gears in place. I manually turned the gears to set the pontoons parallel and they have not shifted position at all.
All of the removed electronics weigh 6.2 ounces. The equipment that took its place weighs less than a single ounce. The main component is a Tactic TR624 2.4GHz receiver. It is a 6-channel receiver, but I'm only using 2 channels here. The only other components were two 20-amp Electronic Speed Controls (ESC) for the brushed motors in the pontoons.
The transmitter I chose is a Tactic TTX650, 2-stick radio. As with most 2-stick radios used in the US, fore/aft movement of the left gimbal is not spring-loaded to return to center when released. It simply stays where you put it. I modified the gimbal on this radio so that this movement would self-center. The main idea was to set up the controls like you imagine driving a tank. Moving the left gimbal fore and aft would control the throttle of the left pontoon, while the right stick would be connected to the right pontoon's ESC.
My original plan was to use ESCs capable of forward and reverse operation. However, the only ESCs I found in my stash are forward-only. I decided to press ahead with these units, figuring that I could invest in reversing ESCs if my initial results were positive (I ordered the new ESCs yesterday).
Each ESC was soldered to the motor leads from a pontoon. The left ESC was then plugged into channel 3 of the receiver, while the right ESC went to channel 2. Like most modern ESCs, these units have a Battery Eliminator Circuit (BEC) which uses the vehicle battery to power the radio gear with a 5-volt feed. I removed the red wire from one of the ESC receiver plugs to prevent the BECs from interfering with one another. The power input leads were combined in parallel and joined to a single XT-30 battery connector. I am using the same 3S-850mAh LiPo battery from my earlier 3-cell tests.
There is plenty of room in the front of the Twister's body for the receiver and ESCs. I cut a hole in the floor of the battery compartment for the XT-30 to poke through. Then it was time to reinstall the top of the body and go for a test drive.
The Modernized Terrain Twister
We had a few 50-degree (F) days that melted all of the snow and left my yard with a large, deep puddle surrounded by mud. This was good proving ground for my modifications. Did I mention that the Terrain Twister floats?
The improvement in control afforded by the individual, proportional throttles was immediately apparent. I was able to get the vehicle moving gradually, rather than the lurching full-throttle starts of the stock system. I was also able to turn with much better precision by using more or less throttle differential.
The Terrain Twister transitioned seamlessly from the mud into the puddle and back. It never even slowed down. Much of the puddle was deep enough to float the Twister. It performs quite well on the water. I was really surprised by how nimble it is. It splashes a lot of water while it moves, but the body stays mostly dry.
Later that day, the warm spell was replaced by a storm that brought 6+ inches of snow. The Terrain Twister didn't perform nearly as well on the fresh, fluffy snow. In fact, it often became stuck. I moved to plowed areas with a thin layer of snow bordered by nice, dense snow banks. The Twister was once again at home. The 3-cell battery provides good speed, while the updated radio is much more authoritative. I can't wait to install the reversing ESCs for even more control options.
Ready for More
This cheap experiment has really made me wonder about the performance potential of screw-propelled vehicles. Throughout this whole process, I still have not cracked open the pontoons to check out the motors and drive systems of these toys. Rest assured that I will be doing that soon.
I recently bought another used Terrain Twister on eBay. It should be arriving any day. This one did not include a stock transmitter. That doesn't matter to me since it will immediately get gutted and equipped with a Tactic receiver. I will then see if there are any logical ways to REALLY get those pontoons spinning. If I find something that works, I'll be sure to share it here.
Check your attic and local thrift stores for toy-grade RC stuff. Many of these machines respond well to a little TLC and a simple battery upgrade. Others, like the Terrain Twister can be the foundation for an even more-exciting project!
Terry is a freelance writer living in Buffalo, NY. Visit his website at TerryDunn.org and follow him on Twitter and Facebook. You can also hear Terry talk about RC hobbies as one of the hosts of the RC Roundtable podcast.