I recently came across a Wild Thing Modification by the Barstow School and FRC Team 1939. They did a really amazing job and the end result looks great and is very functional. Seeing what they had done I was inspired to get a Wild Thing, see how it worked and begin to explore what else I could push it to do including remote control and eye gaze control.

For the Barstow School project they opted to completely replace all the of the toy’s electronics including motor driver. There are some advantages to that approach including no need for reverse engineering and also having complete and direct control of motor drive parameters including the ramping up and down of speed. But still, I thought it would be informative to see how far one could get by keeping most of the toy’s electronics in place and just emulating the joystick sensors to control the Wild Thing. After getting this working it deserved a real test so I added remote control:

Having already worked out everything about the controls to get that working, it was trivial to switch adapt the toy as shown below. Speed, ramping, momentary vs latching, etc. can all be tweaked as desired.

Lastly for this round of tests I hooked the Wild Thing up to eye gaze based driver controls I created. In the video below the eye gaze setup and myself as the driver are outside the vehicle, but of course the eye gaze could be mounted to the toy itself allowing the rider to drive using only their eyes.

Pictures of the unmodified Wild Thing including the control electronics under the seat in the battery compartment:

Looking at the wiring my first surprise was how many wires were on the joystick ports on the main board. I thought each joystick would be a pot, which would be 3 wires, but instead I saw 5. Taking apart the joysticks I saw that they used a combination of magnetic pins with sensors and a flex sensor for each joystick. These same magnetic pins with sensors were used in the seat switch, surprising me again as I would have thought they would have just used a mechanical button or microswitch.

Pictures of the joystick electronics:

Pictures of the seat sensor electronics:

After first working out GND, I probed the voltages on each of the other joystick wires as I moved the joystick through its full range. To do this and to set myself up to later inject signals I cut and stripped the wires and soldered on header pins.

Having worked out all the sensor output voltages it was easy to emulate the joysticks with 2 DAC outputs each and the seat sensor directly with a GPIO. DAC was the simplest way to go for the joystick wires since one of them was not high impedance and would sink 3 mA at the center voltage.

JOYSTICK:

  • yellow = GND
  • black = mag sensor
  • green = flex sensor
  • white = indirect 3.3 V
  • red = 3.3 V
  • CENTER: black = 1.49 V, green = 1.65 V
  • FULL FORWARD: black = 2.68 V, green =3.03 V
  • FULL BACK: black = 2.68 V, green = 0.01 V
  • Anywhere In Between: black = 3.28 V, green = proportional value in between (eg. mid forward = 2.3 V)
  • NOTE: for the second joystick the range is reversed.

SEAT SWITCH and SPEED SELECT BUTTON:

  • black = GND
  • red = Battery +, around 13 V
  • white = Speed Sel button (high Z input: 3.3V released, 0V pressed)
  • green = Speed Sel button (high Z input: 3.3V released, 0V pressed)

For sake of completeness, I’ll also document that the motor driver uses 30 kHz PWM and that the motors can pull a total upwards of 6 A under strain.

This toy definitely proved to be very hackable and versatile. Please note that these control modifications (remote control, switches, eye gaze) are not limited to this modification method. They could have just as easily been implemented on top of replacing the motor driver if desired.

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18 Replies to “Reverse Engineered Wild Thing”

  1. Bob, I freaking love your work man! Do you have any familiarity with transparent eye-gaze controllers? If the screen were transparent it would prevent the rider from having to choose between steering and seeing where they are going. Really awesome work as always! Thanks for sharing!

    1. Thanks man! I haven’t seen transparent eye-gaze controller package but 2 alternate methods I’m aware of include:
      *showing the view from a forward facing cam as the screen background
      *doing eye tracking without a screen, just the eye-tracker camera
      I seen other projects using variations of those and some of my future work will explore those options as well. To your original idea, there are transparent screens by LG and others that may be more of an option as the price comes down and they’re more mainstream.

    2. Thank you so much, Bob! One of our kids cannot engage both the weight switch and the motor controls at the same time. They have to lean forward using trunk force to move the joysticks which unweights the seat. We want to rewire the seat and speed control switch to use an on/off switch and a potentiometer for speed control but are having a hard time determining if this would be possible based on what input the wild thing controller is expecting.
      Do you have any suggestions on wiring or possible solutions?

  2. Wow- I’m a physical therapist and I freakin love engineers! Are you planning to distribute your schematics to somewhere like UCD Go Baby Go?

    1. Thank you for your comment! Do you work with any families that need one? We are currently customizing and selling them. We would be happy to talk with GoBabyGo if they were interested but this is a level of electronics and customization far beyond what they currently perform. We configure these for eye gaze, voice control, EMG, etc.

      1. Hello Jim,
        Thanks for your question and my apologies for a slow reply. I encourage people to contact us at accessredefined@gmail.com so we can gather the necessary information and provide an accurate quote, especially since there are many ways we can customize the end result to fit specific needs. But for either of those you mention, including our warranty and a remote control (so that the adult helping can override the controls providing an extra layer a safety and functionality) the ballpark is around $2K.
        Bob

  3. Can I ask where you got your added back seat or what it’s called? We purchased a wild thing for our son with SMA and he will need a bit more head and truck support and the blue seat in the photos looks perfect. Thanks for any advice/info!

  4. Bob, thank you for posting your progress. I am in the process of adapting a wild thing for a student at my school. Working on making child control mode and parent (remote) mode. Your ideas have really helped me organiz my thoughts on this! Great work.

  5. Bob! I LOVE this! Do you have instructions on how to control the speed and hook up the switches with the pre-existing hardware? Are you able to get it slower than the preset speeds?
    Have you tried an uprider from Rollplay?

    1. Thank you Margaret for your comments. To hook up switches and control the speed you need to add some amount of custom hardware/electronics beyond the pre-existing hardware. Though you certainly don’t need to go as far as we did, including the remote control, etc. Using their motor controller you produce slower speeds by simulating smaller joystick deflections. If you replace their motor controller than you can directly achieve a very slow speed. I don’t have any experience with the uprider yet but it looks like fun.

  6. Bob – love the article and the ingenuity. I bought one of these for my son – he can use both hands, so we don’t need to add a joystick or remote controls. He plays wheelchair basketball and wants to use it to go get balls from the yard – tough to wheel thru the grass.

    I was wondering, though how we could eliminate the switch. It is very finicky – ours stops all the time and then starts again after you move around. I added a toggle switch for on/off and have forced the switch closed mechanically – it is better, but it still gets stuck. I don’t know what to do with the four wires to eliminate the seat sensor board. I would be OK with setting it on 5mph and leaving it there if that helps?

    1. Hi Mark,
      Thank you for your comments. The Wild Things I’ve seen seem to “go to sleep” after some minutes of sitting “idle” and only a “seat cycle” or power cycle wakes it up unfortunately. If it’s not the idle issue that’s getting you I wonder if it’s just a faulty switch. The manufacturer put some pretty thoughtful safeties into this product but for some specific uses these safeties get in the way.
      Best,
      Bob

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