stepping power

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Dr_Doggy

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I got this little robot here that im running with my L297&298 driver I used the schematic in the datasheet and it works good simulating the controls (even a 6 volts(0.5amp) but when i put him on the ground the motors dont seem to have enough torque. and the motors skip and arent able to make the complete steps, instead just vibrate around a lot

my carriage is about 1or 2 lbs, and my motors are rated up to 24 volts, when on i am using 12volts and 1amp, shouldnt' that be enough power to spin the tires?

Maybe there is a way to modify my circuit to improve my performance, or maybe im doing something wrong?
 

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Stepper motors are basically low speed motors. If your step input frequency is to high/fast they will skip and shudder. For faster speeds they have to be ramped up, start slow and increase speed slowly.

Some good information on steppers; Jones on Stepping Motors
 
If you use a normal 3-pole motor you need a:
MOTOR SPEED CONTROLLER
Most simple motor speed controllers simply reduce the voltage to a motor by introducing a series resistance. This reduces the motor's torque and if the motor is stopped, it will not start again.
This circuit detects the pulses of noise produced by the motor to turn the circuit off slightly. If the motor becomes loaded, the amplitude of the pulses decreases and the circuit turns on more to deliver a higher current.
**broken link removed**
 
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Running the motors at half voltage is at least part of the problem.
 
If you are trying to direct-drive the wheels using the steppers, that might be an issue, too - you might need to introduce some gear-reduction...
 
ya,! i think i messed up on all 3 of those things, when i slow the clock down enough he twitches a bit, he makes the step but cant hold it, I was just reading about that dead zone posted is that what im facing? , is there a way i can give it a kick?

@ 12v 1A it should put out 12watts, so thats 12joules on about a kilo, Ek=M*V*V/2, so shouldn't I have a fair bit of acceleration behind me?
 
Quote doggy " he makes the step but cant hold it".

A stepper motor needs to have one coil activated to retain its position, unless it is mechanically loaded by it's drive system. By that I mean gears or in a machine a screw drive.

A stepper that is direct connected to wheels will free wheel until gravity or surface roughness will stop it. The clock input on the L297 needs to stay high, not toggling, to do this if you don't use a gear reduction to your wheels.
 

switch the crap from ST to a 2.5A Allegro MOS translator part, give it at least double the voltage on the power rail, take 2 aspirin and call me in the morning!

a microstepping controller will help the low speed and switching to full stepping will help at high speed. the high input voltage allows the motor to go faster. steppers are NOT voltage run devices, the voltage is just what you can apply DC wise and not overheat it
 
How much current does your motor actually draw at 12V. If it's less than 500mA, then connect a high torque driver to the motor. Keep to coils high, and when the circuit is switching to the next coil, you still have one coil that is active to hold the motor in place. A simple high torque driver can be made using a set of flip-flops.
 
hey thnx, those hints were all great, turned out my timer was shot and sending weird signals,,

Another thing I am experiencing is that when my clock is slow my tires tend to jump around anonymously, but at higher frequencies it seems to spin up normally(unloaded) , could my wiring to the motor coils be backwards?
 
Also I have another problem,, I am using a 6v 4500ah battery on the bench, the draw of the bot is 1.3amps, but when I switch to a 9v battery, 1)something goes wrong with the clock, i think it weakens so the L297 cant read it or something
2)the current drops in half (0.75amps) on the bot, but the battery reads 1.75amps when connected direct to the ammeter
 
What type of 9V battery? A 9V transistor battery is not designed to provide more than a few hundred mA.

Did you connect the ammeter directly across the battery? That's a no-no since it shorts the battery. You always connect an ammeter in series with the load.
 
ya, i kno, it was just for a sec, to make sure i had enough current, actually i took 4 rectangle 9v batteries and put them in parallel, I got it to go up to 1.8amps direct to the meter,, thats why im wondering if maybe im still under powered, even though my measurements say im well over?!?
 
The battery short circuit current is much higher than the current it can supply at its rated voltage. What you are actually measuring is the approximate internal resistance of the battery which is 9V/1.8A = 5Ω. Thus, for example, allowing a 1V drop in battery voltage, the battery could deliver 1V/5Ω = 200mA.

Yes, you are quite underpowered.
 
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hey thnx! I replaced it with my LiPo battery, sized down the tires and re tuned the timer, working much better now!
 
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