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Tic T500 driving a Leadshine ES-DH2306 servo driver


#1

I am trying to use the Tic T500 to generate a pulse output to drive a large servo driver, the Leadshine ES-DH2306. I know this is not what the Tic is intended for, but it is the best thing that I was able to find. I am using an Arduino Uno clone (the Controllino Mini). By using the Tic I am able to generate higher frequencies and not tie up resources on the Arduino. I also like the ramping feature. The wiring is simple with the Tic to the ES-DH2306, I am connecting the A1 and A2 on the tic to the opto coupler pulse input on the ES-DH2306. The setup is working well, but with one major problem. The distance traveled is not linear. I am using the servo to drive a wire puller. For example if I set the travel distance to 10,000 pulses it dispenses 11 5/8" of wire. If I double the pulses to 20,000 it dispenses 25 5/8" of wire (more than double the distance). I have set the ramp acceleration and the top speed low enough so that slipping should not be a problem. I should also mention the servo uses a closed loop system so its distance should be totally linear with the pulse count received. Does anyone know why I am not getting linear results and how to fix this? Also I really wish Polulu would make an I2C pulse generator with ramping specifically for driving large servo and stepper drivers. I could not find anything on the market like this and I suspect there would be a large demand. Any help would be much appreciated.


#2

Hello.

That is an interesting use of the Tic. You should probably use the STEP and DIR output pins on the Tic instead of the A1 and A2 outputs. We designed the board so it can be used like that and we intend to eventually produce a version of the board without a driver IC. The A1 and A2 outputs are meant to control the current through a coil with feedback and not ideal for controlling a high impedance logic input.

-Nathan


#3

Hi Nathan,

Thanks for the great info! When I read the documentation I saw that the step and direction pins are inputs. I didn’t realize they can also be used as outputs. That makes me very happy. I also may have solved the linear problem. I plotted the data for various different lengths and it looks like the data is indeed very linear. I just need to talk to some math people to figure out how to turn the data into a line formula. Math is not my forte. Thanks again!

~Mike


#4

Thanks for letting us know it worked. There’s more about using those pins as inputs or outputs in the “Setting up STEP/DIR control” section of the user’s guide, if you are interested.

-Nathan


#5

Hi Nathan,

I tried hooking up the motor controller to the step and gnd pins as described. The motor moved extremely slowly even when I raised the top speed to 50,000 pulses/sec. Any idea why this would happen? It is working fine when I drive it with the A channel. I could find very little information about using this output in the documentation. Also I did a linear regression to find the formula for pulses given mm. It is extremely linear now. Is there any reason not to keep using the A channel if it is working? I know the H bridge reverses with a bipolar stepper driver, but the LED opto coupler should block the reverse current. Thanks for your help.

~Mike


#6

I tested a Tic T500 here with a very small load (100k) across the A channel and the voltage at the A1 and A2 pins do seem to make a relatively clean square wave (relative to ground). If those seem to be working in your system, it might be OK to use them that way so long as the load on the output is small enough to avoid triggering any current limiting. By the way, the stepper driver changes which of the A1 and A2 pins is connected to ground and which is connected to 12V, it does not supply a negative voltage to either of those pins. You should not connect either of those pins directly to ground or any voltage supply, but that doesn’t seem to be a problem in your case.

It is unclear why you noticed a slower movement using the STEP pin; the output signal from the A and B outputs is about 4x slower than the output from the STEP pin in full step mode (and becomes 8x slower in half-step mode).

-Nathan


#7

Hi Nathan,

Thanks for the info. I assume you mean the TIC’s motor voltage supply when you said 12V. In my case it is 5V. It occurred to me, does the STEP pin put out PWM? If this is the case it would explain the slow speed as PWM changes the pulse width, not the frequency. Maybe some time I will hook up an oscilloscope. At the moment it is working perfectly though, so I am not too eager to mess with it :wink:.

~Mike


#8

Yes, by 12V, I meant the Tic’s motor supply voltage (VIN).

The signal from the output channels (with a high impedance load) is a square wave with a fixed 50% duty cycle. The output of the STEP pin is a fixed on width (about 3.75 microseconds) square wave at the frequency of the specified step rate.

-Nathan