I was just looking through the Lego catalog and noticed that Lego has gotten even more expensive than Vex, it seems. For a single touch sensor, it costs $17.99 USD. You can get 2 limit switches for $12 USD. So… the lego sensor costs 3 times as much as one limit switch. The NXT brick costs $144 USD, and the Vex costs only 6 dollars more, and is much higher quality with more processing power and ports. Just wanted to put that out there. No longer does lego have the “more affordable” edge that drew people into buying it.
Wow… This is a shame. I still have my old touch sensors from NXT. I’ll upload some pics of the inside of one of these things!
It is definitely not worth $17!
Haha! That’s should be worth 50 cents!
I forgot to mention that the switch has 0 tactile feedback, so instead of a nice hard “click” you get a “mush” feeling. Very cheap.
Please check your facts correctly. The NXT brick is 4x more powerful CPU than the Vex 0.5 processor, and also has much more memory.
Now, if you are talking about the new Vex ARM processor, then you are just matching the NXT in power.
Paul Tan.
Looking at the specs it is quite a bit more powerful with the ARM7 uP, but Vex has many more I/O ports(NXT can only have 3 motors and 4 sensors).
Hopefully we haven’t started a Vex vs. NXT war…
I hadn’t realized that the Lego has an ARM7… I guess that I felt so limited because of the memory intensive and limited porgramming software it comes with. But still, what’s the point of having all that memory if you can only use 3 motors and 4 sensors?
Your program might need massive variable storage for a very complex program.
Yet it might only use 3 I/O pins that are doing serial communication.
RobotC is not too bad for the NXT, it is actually quite fast and you can do a lot with it.
If you are doing FTC, the motor controller and servo controllers will actually let us connect up to 8 motors and/or 24 servos to a single NXT brick, in addition to having 3 lego motors.
http://parts.ftcrobots.com/store/detail.aspx?CategoryID=161&by=9&ID=6356&c=1&t=0&l=0
The nice thing about the FTC motors is that they are 3x more powerful than the Vex motors (We are both an FTC team and a VRC team, so have used both systems)
Paul Tan.
Coach of Polar Bear Robotics
VRC Team 2027
FTC Team 27
Wow… I greatly underestimated Lego. The Tetric motors are about 3 times as powerful as Vex’s and are faster…
Wait a minute, disregard my last comment. The specs are at a different voltage, so you cannot directly compare them. The Vex motors have 102 oz-in torque and 100 rpm at 7.5 volts, and the Tetrix motors have 300 oz-in torque and 152 rpm at 12 volts. Since rpm can be decided upon, as the voltage is directly proportional to rpm, we can assume that:
Vex motors: about 13.333 rpm per volt
Tetrix motors: about 12.66666 rpm per volt
Since torque has a disproportional curve with voltage, one cannot assume the force. I guess somebody will just have to test it themselves.
We have tested them. We have both an FTC robot here as well as a Vex robot. I can tell you right now that for an arm of similar weight and length, we can drive it with a SINGLE Tetrix motor, and it is quite fast. On the Vex robot, two motors COULD NOT even lift the arm, let alone the payload.
I know if you go by the Torque specs, the FTC motor should only be about 1.5 times better than a Vex motor, but our practical experience shows us that the FTC motors are really about 3-4x more powerful than the Vex motors.
Paul Tan.
Coach of Polar Bear Robotics,
VRC Team 2027
FTC Team 27
Is that using 12 volts for Tetrix and the standard 7.5 for the Vex motors?
It is using 12 Volts for FTC.
Well, there’s no real comparison there. Since you are using a higher voltage for to Tetrix kit, of course it will perform better. If you had the Vex motors running at 12 volts (which you can do, up to 15 volts) they would perform much better than they did before, coming close, if not equal to, the Tetrix motors.
And you could probably feed the Lego motors 18V and get more speed/torque of them (for a while). I don’t think it is fair to compare the Lego motors at their rated voltage against an overdriven Vex motor. Overdriving isn’t even an option for (most) competitions, but if you want to evaluate them that way, then you should overdrive them both to an equivalent point beyond their design spec.
Cheers,
- Dean
Ummm… if you tried running the Vex motors at 12 volts, they would burn up and melt the copper because the windings are not designed to take that much energy.
I don’t quite get your point?? Aren’t we comparing motors in respect to what they are designed for?
Enlighten me on what you are trying to get at?
Vex motor specs:
Free Speed 100 rpm @ 7.5 volts (performance varies slightly due to variations in manufacturing)
Stall Torque 6.5 in-lbs (approximately)
**Max / Min Voltage 4.4 - 15 Volts (Motor life will be reduced operating outside the VEX Controller range of 5.5 - 9.0 Volts) **PWM Input 1ms - 2ms will give full reverse to full forward, 1.5ms is neutral
Nominal Dead Band 1.47ms - 1.55ms
Weight 0.21 lbs.
Wiring Black - ground; Orange - (+) power; White - PWM motor control signal
Current Draw - (+) Power pin 5mA to about 1 Amp. at stall per Motor
I think that explains you can run Vex motors on 12 volts, although reducing life, they are rated for it. Anyway, my point is, since you said that the Tetrix motors are 3x stronger than the Vex ones, the Vex motors may be just as strong if given the same amount of voltage as a Tetrix motor. Quazar, I don’t understand how you don’t thinking running both the Vex motors and the Tetrix motors at the same voltage is unfair. I thought we are talking about strength of the motors, not the power you will get out of them when using the designed controller. In this case, the Vex microcontroller is giving the motor less power than the Tetrix controller, and that is a variable, so the results are invalid. Granted that you set up an H bridge, you can be running the Vex motors like normal but at 12 volts. Then, and only then, could you actually compare the motors. What you are doing is basically like comparing the smarts of two kids, one with an education, and one without.
My point was simply that you could also run a Tetrix motor at a higher voltage than the system usually does and probably get even more power/speed out of it in exchange for a shortened life. There are lots of ways to compare motors, and they can all be valid depending on exactly what you are trying to determine.
If your goal is to compare the motors at a specific voltage, say 12V, then your methodology is fine. You will get a result that is valid for operating at 12V and does not take motor life into account.
If you want to consider motor life, then it gets more complicated since we don’t have derating curves for each motor. Also, duty cycle is important since most robot motors are not run continuously, giving them some time to cool.
Lacking detailed spec sheets for the motors, I would only compare them at the voltage limits of their intended control systems, since they are presumably sized and tested specifically to operate within those limits.
- Dean
Well, the VEX programing language is more versitile, and the lego NXT has stronger motors (Don’t question me, I checked), but the thing I love about the VEX is that it can hold up to 8 motors! (Unlike the NXT which can only hold three). So, overall, I would recomend the VEX for more experienced builders and the NXT for begginers.