4-wheel robot chassis (looking for input)

Seairth

For some time now, I've been thinking about doing an autonomous 4-wheeled robot. The thing is, as this is mostly of a learning/experimenting thing, I want to keep the cost down. To that extent, I've been keeping an eye out for a commercial R/C toy that I could strip down. My two main criteria have been:

* large enough to support prototyping hardware, sensors, etc.
* drive-train is either tank-style or 4 independent motors (no Ackermann steering).

As it happens, the nearby Costco currently has a New Bright Mega Blast R/C Truck (Amazon link here) that meets both of those needs at a price of $80. My intent is to strip the electronics down to just the motors (and maybe motor driver circuit, but probably not), remove most/all of the "truck" shell, and build a platform (partly on top, and partly suspended below to lower the center of gravity). There is a separate motor for each wheel (which are rubbery, not hard plastic), and the 1:8 scale (it's something like 26"x14"x14") should be plenty big enough to hold some weight. Reading through customer reviews, though, there are a few concerns: apparently, the motors are loud and the battery life is short. I can always add more battery, but I'm not sure what to do about the motors. Since it's not likely that the robot will drive around at full speed, this might not be that big of an issue. Though it will add cost, it might also be worth replacing the motors with some better-quality ones (maybe even reduce speed for some additional torque).

So, for those of you out there that have done this sort of thing before, what are your thoughts? Since this is entirely new territory for me, I'm hesitant to start down this path without knowing how feasible this approach is. Any suggestions, alternatives, gotchas? (note: first, I mostly need to know if it's worth buying this thing or not. Costco tends sell through these things pretty quickly.)

erco

I'd steer clear. That link has a video which is all CGI for a reason. New Bright is always the cheapest car around. Looks like the $80 is spent on sheer size and a loud horn, probably not speed, power, maneuverability, durability or quality. It's low toy grade, designed to maybe satisfy a kid, but I bet overall you'd be much happier spending a bit more at a hobby shop. At least find a real video on Youtube of this or whatever you consider buying. And test it indoors to see if it meets your expectations for power & maneuverability, and return it if you have any doubts.

Funny, I recently selected a Walmart $10 New Bright car for a magazine article project, just because it was cheap and readily available, and it was not a high-performance application.

Edit: You might look on Craigslist or such for a good deal on a used hobby-grade dune buggy with suspension and shocks. Those guys are always upgrading and looking to sell last year's buggy.

xanadu

There are videos of it on youtube.



The last time http://forums.parallax.com/discussion/160715/looking-for-1-10th-scale-rc-rock-crawling-truck-to-hack I wanted to build something similar I watched craigslist for a beat up Traxxas, that wouldn't meet your steering requirements but there could be other stuff that does. I never bought anything, in the end I decided wood and aluminum would be easier.

Seairth

Thanks! I will continue to look elsewhere, then.

xanadu

Who will be the first? $280 it won't be me https://www.sparkfun.com/products/13141



I saw a bunch of Actobotics stuff at Fry's the other day. It is light and looks really durable. Fits the steering reqs. I'm not sure about the 4x 313 RPM HD Precision Planetary Gear Motor motors. 150 RPM is a lot to me.

Duane Degn

I hesitate to suggest it but Dagu's Rover 5 is a relatively inexpensive way of getting four gear motors and four quadrature encoders.

Here's a thread about my Rover 5 with threads where I discuss my love/hate relationship with the Rover 5. I bet you'll want something a bit beefier than a Rover 5.

I'm personally a fan of motors with quadrature encoders. I've been impressed with how well one can navigate using odometry from quadrature encoders.

erco

Actually xanadu's video makes it look better than I expected. Apparently the springs & suspension actually let the axles move a bit, of course there are no shocks so the ride is bouncy. For $80, it's probably fine for light duty use, as long as you accept that you can't buy standard replacement parts nor easily upgrade anything. It's disposable, so you might consider buying a backup vehicle for parts, or just to swap your electronics into when the first one gives out.