12 May 2006

The VEX robotic kit, a newbie review


As I've mentioned in a previous entry, I bought the VEX robotic kit from Radio Shack, for 150 USD. The normal price is 300 USD.

I've always wanted to build a robotic tank with an autonomous mode, where it can act like a primitive living being. I mean, simple stuff such as hide from the light, navigate through a room, run from sounds, and so on.
This seemed to be very possible with the VEX kit, and it is indeed possible if you are willing to make a few concessions.
The first concession is that the price is very high. For example, you will need the following:

a. The starter kit (150 USD from RadioShack, or 300 USD from VEX). Radio Shack has them on sale until June, I believe.

b. The basic programming kit is on sale for 50 USD from RS, but you can't find it in stock, so you'd have to buy it from their site, for 100 USD, or from eBay, for about 70 USD. However, from reading their tech support forums, it seems that unless you are content with their EasyC*, you will need to buy a prototype kit from them. They do not display the price for the prototype kit, you will have to call them on the phone to order. That kit has the same price, of 99 USD. I just ordered it now, and should have it here next Friday.

*The EasyC thing is an interface where you don't really write C code, but just use some diagrams, and it builds the code for you. That's nice for the beginners, but for advanced programmers it's unacceptable, as you can't write your own custom code, can't have your own functions, and so on. They have a version of EasyC 2, which is an additional 50 USD(!), and it's supposed to be better, but since I didn't try it, I can't comment.

c. You will also need a track kit and a few sensors, which can be over 100 USD in total.

So the total cost is about 500 USD, and more if you want more sensors and motors. As a side note, the max combined output is only 4A, so since a motor can use 2A it makes no sense to use for example 2 motors on each track. So only buy motors if you plan to use them independently.



The documentation for the track kit is sublime, but completely useless. It doesn't describe the most important feature, which is how to connect the god damn gosh darn motors in a reliable way. Looking on their forums, some people also complained about it, and had the same problem I had: When taking turns, the axis connecting the motor to the wheels was slipping out off the motor...
Reading an article on botmag.com helped, because those guys are experts and had the same problem had. They solved it by adding a second support rail. Unfortunately that article is not very detailed about how the bot was constructed, so I had to look at the pictures and steal some of their ideas. However, the pictures do not show all the angles, so I had to do some trial and error tests. Right now, I came up with a very good idea, and the preliminary tests are promising. My tank is almost done, and you can see some pictures of it. The receiver is not placed properly yet, because I want to put some solar panels on top of the tank, and the antenna might get in the way, which is why it will be placed at the end of the project..

The technical support is very... unique. They do have a forum, and they do respond the questions in a timely manner. Usually they respond to them in the same or next day.
However, most of the answers are a little bit ambiguous, so to say. For example, I've spent a few hours last night to find if I can program it in assembly, using the standard programmer kit. There was no definite answer, so I had posted my own question. As you can see, the answer is more or less: "Ask the company that made the compiler".
I mean, WTF, the starter kit + the programming kit is 400 USD, I'd expect a little bit more descriptive answer.
To make things worse, their policy is to not let anyone but the admins respond to the posts, and once a post is answered, it is locked, so no follow ups are possible.
I personally believe having an open forum, where the community can interact would be a very good idea.
One other bad thing, IMHO, was that some technical questions posted by various people were answered with: "That's confidential, sorry". That is, IMHO, doubleplusungood, as it is an anti innovation practice. I believe they should open source their protocols so that people can hack those bots and create things that are otherwise not possible, such as connecting the transmitter to a computer.
The questions, however, are answered by their engineers, which is a good thing. I hope that in the future they will have better technical support, and a forum where people can interactively discuss about their projects and share their knowledge.

The starter kit is very nice, (especially if you buy the tracks kit, which is on sale at RS for 15 USD) and it's well worth 150 USD. But I wouldn't buy it from their official store, for 300 USD. That's a lot of money, and there are better kits out there.

Conclusion:
Pros:
a. Very versatile kit, you can do a lot of stuff with it.
b. Lots of add ons.
c. There are new things in development, such as new sensors and new hardware.
d. Newbie friendly, but powerful enough for the intermediate and advanced user.
e. The programming kit is easy to use for the beginners (also see cons).

Cons:
a. Pretty expensive.
b. The documentation is lacking.
c. Tech support could be a little better.
d. The standard programming kit is not good enough for the advanced programmers, but they can buy the prototype kit for the same price.
e. Some information is confidential.

2 Comments:

Anonymous Alexander said...

Seems you have some problems with your robot building. I have used parallax.com to buy my components and the Basic Stamp to build different robots. Maybe its too late now when u already bought a VEX. But i still want to recommend www.parallax.com, it is a very good system.

13/5/06 05:00  
Blogger Lost said...

You had suggested programming it to "hide" from the light. But I think that based on your other experiments I can see you programming it to sit in the sun for a time each day to recharge, once you have installed the solar panels. ;)

17/5/06 20:18  

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