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I have zero experience with robotics, but I need to build a mobile platform for a streaming camera. The idea is that I'll plug in my Android phone into the pan/tilt unit on my wheeled robot and then drive and look around via WiFi. I have already solved all of the software, interface and controller issues, but I would appreciate some advice on how to build the wheeled platform.

My initial idea was to buy a cheap RC car, remove all electronics and replace them with my own. This approach almost worked. I purchased this New Bright F-150 Truck. The size is good and there is plenty of storage space:

New Bright F-150 Truck enter image description here

However, I quickly ran into a problem with this thing. I assumed that the front wheel would be turned by some kind of servo. Instead I found this nonsense: enter image description here enter image description here

That small gear shaft is not driven by a servo - it's a conventional motor, which spins until it is jammed at the extremes of travel. The wheels are straightened when power is removed by a small spring on the other side. This means that there is only one angle at which the wheels can be turned, and that angle is way too small for what I need. So using this RC car will not work.

Before I start buying more things, I would like to hear some opinions from more experienced people. Am I on the right track? Do I simply need to get a better RC car, or are they all designed like this? Perhaps there are other options that would be more suitable for what I am doing?

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  • $\begingroup$ From what I know, they use what you have said, an RC Servo to do the steering. Be in mind that adding a feed-back to that mechanism (well designed, nothing non-sense) will turn it into a servo. If you don't want to build your own platform, then yes, the more costly one should use a RC Servo to steering, just be sure before buy. You could add one to that, but its not clear if the angle is too small by the actuator mechanism or by the king pin itself. $\endgroup$ – Diego C Nascimento Jan 24 '14 at 15:54
  • $\begingroup$ I second what Diego says, but if you're willing to purchase some extra hardware, why not buy a mobile robotic kit, a Lego Mindstorm or perhaps a Parallax Boebot would serve your purpose elegantly. $\endgroup$ – metsburg Jan 29 '14 at 4:57
  • $\begingroup$ @metsburg well its says it wanted a cheap one :) I used much Lego when I was a kid (theres no mindstorm in my time we used small brushed DC motor with rubber pulleys), but I don't think they will perform good as a educational for professional projects, as this is the case you encounter with professional projects. With Lego you get a piece and has the correct mounting, in real hardware you need to machine things to work, and is not always easy. $\endgroup$ – Diego C Nascimento Jan 29 '14 at 22:48
  • $\begingroup$ Yes, all economy robotic kits will be a bit shaky, things may not be very professional... I agree. I would suggest Pioneer 3DX, if available... but they're not cheap. $\endgroup$ – metsburg Jan 30 '14 at 4:53
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You may replace tgis with an RC servo, but be sure to have enough torque and prefer metal gear.

The steering will involves a lot of mechanic constraints.

Anyway, Diego advice is good and you could also keep the actual mechanism.

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Depending on the strength of the spring, you may be able to convert the power to the steering motor to a PWM solution. That would allow you to vary the overall voltage going to the motor, and (hopefully) allow you adjust the balance between the motor force and the spring force -- resulting in an adjustable steering angle.

This would be less preferable than a servo-based steering design, but might be a good last-ditch effort before upgrading to a more capable platform.

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