Positioning Issues Guide
The following guide is intended to solve problems related to positioning issues. Please follow each step carefully and thoroughly. The most serious problems often have the simplest solutions.
I. Check your cabling!
- Are all of the cables connected tightly and properly?
- Is the power going into the signal generator at the correct value? (9V DC 1 amp)
- Are any of your cables excessively long? DB-9 over 25 ft, DB25 over 6 feet, Motor Cables over 30Ft.
II. Check for Mechanical Problems
- Is everything properly oiled and greased?
- Check the integrity of all of the mechanical connections including
- Are the set screws properly tightened?
- Are there proper flats on the shaft?
- Is there any slippage in the belts?
- Are the setscrews properly tightened?
- Are there proper flats on the shaft?
- Are the belts the proper tension?
- Lead Screws
- Have you accounted for the backlash properly?
- Are the nuts worn out?
- Are the nuts properly affixed to the table that they are driving?
- Are the gibs too tight or too loose?
- In a Rack or Gear driven system?
III. Check For Software Signal Compatibility
- Is the Baudrate that you are using capable of supporting the speeds you want to go? For the Lightning Chip the top step rate formula for a given baudrate is approximately:
Baud Rate * 3 / 10 = Max Step Rate in steps/second
For example, if you are going at 115,200 baud, the theoretical max step rate is approximately 34,560 steps/second.
- Check the direction and duration of the pulse width for the step signal and the polarity of the enable line. You should check your documentation from your motor driver supplier for the correct settings. If you are unsure, you could set the pulse width to a relatively high number such as 30 (Note that if the Step Pulse is too high and you are running at a very high step rate, it will limit your top speed.) Then try both high and low settings for the step pulse and enable signals. These settings can be found in the Setup.Motor Signals Menu shown below. Typical settings for the FlashCut CNC drivers are also shown in the chart below:
|Model Number(s)||Description||Step Pulse||Step Pulse Width||Enable Signal|
|5000-0XX-11XXXX, 5000-0XX-22XXXX||2 and 3.5 Amp Full/Half Stepping Drive||Low||15||High|
|2020, 3020, 4020, 2035, 3035, 4035||2 and 3.5 Amp Full/Half Stepping Drive||Low||3||Low|
|2070, 3070, 4070, 2120, 3120, 4120||7 and 12 Amp Full/Half Stepping Drive||Low||10||Low|
|5000-0XX-33XXXX||3.5 Amp MicroStepping Drive||High||3||High|
|C1-3080, C1-3120||Servo Drive||High||10||Low|
IV. Signal Generator Settings
- There are two resistors in the Signal Generator that control the strength of the Step and Direction signals interfacing with the driver box. These two resistors (RP4 and RP6) may need to be removed or changed value for proper use with the driver box.
To remove or change these resistors:
- Remove the two Phillips screws on the bottom of the signal generator.
- Remove the cover and locate the two 9 pin resistor packs RP4 and RP6.
- Carefully remove these resistors from their sockets.
- Replace the resistors with the proper value if necessary. Please note that these resistors are not symmetrical. Pin 1 on the resistor is noted with a dot or a line and should coincide with the white square silk screened on the circuit board under the socket.
- Some drivers, such as our microstepping driver need a very fast, sharp signal coming out of the Signal Generator. For these drivers you will need to replace the optical couplers (PS2501-4) in U10 and U11 with a bank 3906 PNP transistors. The wiring diagram of how to do this is shown in the Wiring Diagrams Appendix of the Hardware Guide. The chart below summarizes how RP4, RP6, U10 and U11 need to be configured for each drive.
|Model Number(s)||Description||RP4 and RP6||U10 and U11|
|5000-0XX-11XXXX, 5000-0XX-22XXXX||2 and 3.5 Amp Full/Half Stepping Drive||None||PS2501-4 Opto's|
|2020, 3020, 4020, 2035, 3035, 4035||2 and 3.5 Amp Full/Half Stepping Drive||470ohm||PS2501-4 Opto's|
|2070, 3070, 4070, 2120, 3120, 4120||7 and 12 Amp Full/Half Stepping Drive||None||PS2501-4 Opto's|
|5000-0XX-33XXXX||3.5 Amp MicroStepping Drive||470ohm||3906 PNP's|
|C1-3080, C1-3120||Servo Drive||None||3906 PNP's|
V. Check For Feedrate Settings
- If the feedrates are too high in the Feedrate/Ramping Setup menu, then the machine can easily loose steps. Remember, the Maximum Feedrate for each axis is used as the Rapid Rate. SO even if you are running a program at very slow feedrates, if you have any G0 moves, they will run at the Max Feedrate.
- The Maximum unramped feedrate sets the feedrate that the motor will try to achieve on the very first step (without ramping). So if your unramped feedrate for a given axis is 10ipm, then the motor will try to move the machine at 10ipm immediately, without any acceleration except for the acceleration from rest to 10 ipm in the distance traveled by the very first step (usually on the order of .0001 - .0002 inches). Keep in mind that this is an extremely high acceleration.
- To see if too high of feedrates is your problem, lower both of the Maximum unramped and Maximum Feedrates by 50% on all axes that are loosing steps. If this helps, then you solved your problem and you can then try to find the best feedrate settings for each axis.
- The ramping settings are usually set fairly conservatively (at 5000 steps/sec/sec) However, if you have a lot of weight or rotational inertia that you are moving, this might need to be adjusted down.
VI. There might be excessive electrical noise in the room, or on your
- Is everything grounded including your computer, and the Driver box? (The Signal Generator gets grounded from the cable to your driver box and your computer.) If your computer is not grounded (and most laptops are not!), then you should strap a wire between one of the lug nuts of the DB25 connector on the signal generator and one of the lug nuts of the DB9 connector on the signal generator.
- Is the outlet in the wall properly grounded with a receptacle for a third round prong (earth ground). You can pick up a device at a local hardware or electronics store that can check if all of your outlets are properly grounded.
- Is there a device nearby, or connected to your system that is excessively noisy? This could be a spindle motor, a plasma torch, a fluorescent light, or any other device that can generate a high power or high frequency electrical noise.
- If so, turn off or locate the noisy device as far away from the FlashCut CNC control electronics as possible.
- Call the manufacturer of the device to see if they make an RF noise filter. Most spindle motor and plasma torch manufacturers carry these.
- Plug the FlashCut CNC control electronics into a separate power strip from the noise source. It is best if this power strip has noise filtering capabilities. It is also best if this power strip protects from power spikes and surges and has UPS (uninterruptible power supply) capabilities.
- Make sure you have clean cabling throughout your entire system.
- All signal and power cables must be properly shielded and grounded. Note that a good cable shield is only grounded on one end. For example the FlashCut CNC Motor Cables are all shielded with the shield grounded to the Motor Driver Box. It is not grounded to the motor in any way. If it were connected to both ends, it could actually cause a ground loop with current flowing through the shield.
- The cables should not be tangled within each other. Especially the power cables should not be tangled with the signal cables.
- Are your Limit Cables very long? If so, they should be twisted pairs and shielded.
- Make sure your cables are not too long. The longer the cable, the more susceptible it is to noise. As a rule of thumb, the serial cable should not exceed 25 feet, and the signal cable between the signal generator and the Driver box should not exceed 10 feet.
VII. Motor Resonance
- Stepper motors vibrate more at different step rates. When this vibration is excessive, it is called resonance. Resonance can cause machine vibration, noise, and possibly lost position. There are a couple of ways to combat resonance:
- Turn down the current to the motor that is resonating. Some times the motor will move faster at lower currents because fo the resonance problem, however, as you turn down the current, you will diminish the total torque that the motor can output. To turn down the current on your motor driver, please see the motor driver documentation.
- Use a microstepping driver, or if you are already using a microstepping driver, increase the number of microsteps per step. To do this, please see the motor driver documentation. A microstepping driver will reduce resonance over a full or half stepping driver by reducing the distance that the rotor of the motor is jumping in between steps.