Let's Make Robots!

Robot gutless and slow....

Ok, so I finally got him put together, and it turns out that he doesnt move worth a damn.... I cant figure out what I did wrong. The tamiya twin motor is set for low range, but it still shouldnt be THIS slow... turning is almost impossible for him... Even on smooth flooring.... I shot a quick video for you all to see and hopefully help me figure out what is going on...


This is the H bridge I am using... SN754410   from sparkfun. The data sheet said i could save pins by hooking the enable pins up to a 5v source, so I did that..... VCC1 is connected to the 5v on the arduino, Vcc2 is hooked up to the same power source as the motors/IC, with common ground. My arduino has its own power source. Ignore the wire coloring, I only had 2 colors and the ones i used here were for my reference, not to indicate hot and ground.

 Power for the board is 4xAA alkaline batteries. Power for arduino is 1 9v battery. 



I have no idea what to do here....
Can anyone help? Thanks in advance.

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That was worded incorrectly. Everything turns freely. Before i changed out the motors, he was running like a champ. Turning was near impossible. now with the new motors and lack of voltage, he cant turn and is slow again, so i need to up the voltage one more time. as soon as i do that, I will see if his turning has improved. I dont think it will have. I will try to take out as much friction as possible as well and see what happens.


"My first thought was that I had locked up all the axles... but i didnt. i made sure one side is turning freely so that when the motor turns the track in one direction, and the other in the opposite direction, everything moves freely. he is pretty much doing the same thing as he was in my video.... "

What do you mean by one side is turning freely? The little idler wheels on one side are moving freely and on the other side are locked to the axles? They should move freely on both sides. Otherwise, the side that tries to turn the axles has to overcome more friction and stops and only the other side is turning. Make sure that only the sprocketed wheels are locked to the axles that come out from the gear box and inside the gearbox the 2 output axles do not touch each other! Try to spin the motors forward and hold one axle and see if the other slows down too. If it does, you've got a problem there. 

ezekiel, they move freely.


My pololu motors came today (gawd they came fast!) and after hooking them up, the bot moves, but very slowly.... there seems to be more turning happening, but only a faction better. I think now that I have motors that can handle up to 12v, its time to get some higher voltage in play. I have a 7.2v battery pack laying here, but I have no way of charging it. I'm sure that if i can get this pack charged and try it, it will solve all my problems.


Does anyone know a DIY solution to charge a standard 7.2 NIMH pack? Its all green shrinkwrapped. the kind of thing you would see inside an rc car. In this case it came out of a portable dvd player that died on me. I'd use the dvd player to charge it, but it is so far beyond toast that all it is good for is parts....


Pop both motors out of the back of the gearbox and check the tracks will definitely move freely in opposite directions spun by hand.

Ok, so i did some rewiring and used fully charged nimh rechargeable AA's and he runs just fine going straight and reverse.... He still grinds to a stop and goes nowhere while turning.... At this point, im so frustrated, im about to put the whole thing on a shelf for a few months.... which i really dont want to do. What would cause him to gind to a halt so hard when trying to turn? My first thought was that I had locked up all the axles... but i didnt. i made sure one side is turning freely so that when the motor turns the track in one direction, and the other in the opposite direction, everything moves freely. he is pretty much doing the same thing as he was in my video.... 


I gotta say though... he has some serious power in straight and reverse now though! I feel so close to completing this portion of the build.... last thing to figure out. Please keep going with the ideas! 

A bit of a puzzle, slowing so much. What I'd try is running the robot on a smooth surface, like tile or a table top. If the same slowing occurs in turns, then there would appear to be a problem with the circuit somewhere, If not, then this robot should not be run on carpet, the tracks simply can't overcome it. Somewhat sad, a tracked vehicle that can only run on smooth surfaces though. 

i just built my first robot , and had a similar problem are you supliying the motor driver chip with some unreagulated voltage? heres a picture of my setup (i pulled out the motors and inputs so you could see) .motor driverS5000658.jpg

the battery is conected negative to the ground on the bread board and postive to the pin that supports unreagulated voltage (check the manual for your chip )

then from the arduino 5v  to the positive on the bread board and gnd to gnd on the bread board . i to powered my arduino with 9v . hope it helps if not sorry (oh and my battery pack has 3 aa's but 4 would be better .

considering the fact that you didnt say what i did wrong frits, i will assume it was the 'help' in the subject line. I have removed this.

Please read the Rules :)

OK, after reading all of the posts, I have to make some comments:

- SN754410 has internal diodes, no need for external ones;

- the motors are poor quality, they suck way too much current and in this particular setup they may actually burn it;

- too wide distance between tracks makes turns more difficult, especially on non slippery surfaces like carpet (if you Google the Tamiya  track kits you will see them with a narrower chassis);

- the tracks seem too tight, that creates extra friction (more load for the motors). 


And now some advice: 

- try to see how the motors are turning when you hold the robot off the ground, if they spin faster,  the motors are either too weak for the robot's weight, or they don't get enough current when they have load; if they spin the same, the tracks are too tight (and perhaps not enough current...).

- tracks are less efficient than wheels, you need to use more powerful motors to account for the added friction

- the narrower the chassis, the easier they turn

- the sorter the part of the track in contact with the ground, the easier they turn.


Good luck solving your problem!