How to create a fast Segway?

[dumpledore]

Hello, I'm a swiss student (mechatronics) and I'm in the middle of my bachelor work. The project consists in creating a Segway that is able to move around at a maximum speed of 4m/s. At the moment,I've assembled the Segway described by Laurens Valk (with the dIMU Gyro), and it works like a charm. I've passed the last three weeks in get used to the robotC Language and the mindstorms environment. I also read Extreme NXT. My problem is, that I've difficulties on how to attach and control alternative motors (with encoders) to the NXT brick. I'd like to understand how to use the PWM signal or how the counters for the motor-encoders work.

I'd appreciate any possible help.
Thx in advance

[pepijndevos]

At Mindsensors, they sell a servo controller, which does PWM stuff. http://www.mindsensors.com/index.php?mo ... PAGE_id=93 The PICAXE also seems capable of controlling servos and motors.

If you are talking about attaching a different motor to the normal motor ports, these are two interesting resources:
http://www.brickengineer.com/pages/2008 ... or-wiring/
http://www.philohome.com/nxtmotor/nxtmotor.htm

Random thought: What wheels are you using? The NXT wheels are rather small, using a pair of these motorcycle wheels that come with the RCX might speed things up a lot.

[hassenplug]

I doubt you'll be able to get speeds like that out of a pure LEGO robot.

This motor controller may be your best bet: http://www.legoeducation.us/eng/product/hitechnic_dc_motor_controller_for_tetrix/1648

Steve

[dumpledore]

Uoh, thx for the fast responses! I use motorcycle wheels (at the school they have all possible LEGO parts).. Ok, the HiTechnic DC Motor Controller sounds to be a good choice. It's possible to attach DC motors with tachos to this? I ask, because fot the balancing task of the Segway I need to control the rotation rate. Do you know other parts I've to buy at any cost?

THX

[mattallen37]

Yes, the Tetrix motor controller supports encoders.

Remember though, that using an I2C motor controller on one of the bit-banged I2C buses will likely prove to have more of a lag than using the built-in NXT motor ports. Normally this isn't really an issue, but it could be for a segway.

I assume you want to use something other than the NXT motor ports because you want more power than they can provide, right? If cost is an issue, you could build a motor controller using e.g. a PICAXE, and run the encoder feedback into one of the NXT motor ports for processing. This would probably also be slightly faster than using the Tetrix controller.

[dumpledore]

This could really be a problem for a segway. The cost of the stuff I've to buy is not a problem at all.

[mattallen37]

So, can you explain what motor power requirements you need to meet? Specifically the voltage and current.

The main thing with segway speed, is that you always need a buffer of additional speed the motor is capable of producing, in the case it starts to fall forwards. The faster the motors are traveling at average, the less of a speed buffer there is available.

[dumpledore]

No, I haven't calculated it yet. Now I'm analyzing the signals from the NXT Brick. Do you know how to function "nMotorEncoder[]" works? I would like to know how the counter of the NXT Brick is initialized, and how the values of the encoder are used. Generally I've the problem that I don't know where the functions of robotC are situated.

[dumpledore]

I bought the Hitechnic DC motor controller and I have attached a dc motor to it. It works like a charm . Thx a lot for the hint!
The dc motor has an encoder shaft with a resolution of 500 pulses (increments). The problem is that I don't find a serious datasheet to the controller and so I don't know how to connect the cables for the encoder. Do you have any idea? The connector for the encoder (on the hitechnic controler) has 4 pins.

[mattallen37]

HT seems to be very closed about that controller. They don't seem to offer any support or information. I have also wondered the pinout of the encoders. If you know some about electronics, you could probably open the controller up, and follow the traces to determine the pinout.