LMS 7x16 Lathe Tachometer Output Port - Compatible with TouchDRO Adapter?

[MaverickNH]

My LMS 7x16 Lathe has a tachometer output port. Is the output signal compatible with a TouchDRO Adapter? I don't know if RPM is actually measured, or if there's just some approximation based on turning the RPM knob on the lathe control panel.

BRET

 

[ycroosh]

I don't know. Haven't had a chance to play with any of LMS machines. If you know anyone with an oscilloscope, it's very easy to find out.
Yuriy

 

[jaek]

The Seig Mini-Lathe and Mini-Mill use a serial protocol to send individual digits to the tachometer display - not just one pulse per revolution.

Some kind soul documented the protocol on his website - http://macpod.net. He also sells a tachometer kit.

 

[MaverickNH]

The Seig Mini-Lathe and Mini-Mill use a serial protocol to send individual digits to the tachometer display - not just one pulse per revolution.

Some kind soul documented the protocol on his website - http://macpod.net. He also sells a tachometer kit.

Good information, thanks! I picked up the LMS-supplied tachometer (at twice the cost) but the port is awkwardly located on top of the control panel. I'll look at rerouting that port elsewhere.

 

[ChazzC]

Good information, thanks! I picked up the LMS-supplied tachometer (at twice the cost) but the port is awkwardly located on top of the control panel. I'll look at rerouting that port elsewhere.

My solution:

Take the back off the readout, attach a Neodymium “mounting magnet” with Nylon screws (so as not to short anything out) and stick on the top of the headstock. The cable ties keep the wire under control.

 

[MaverickNH]

My solution:

View attachment 473569
Take the back off the readout, attach a Neodymium “mounting magnet” with Nylon screws (so as not to short anything out) and stick on the top of the headstock. The cable ties keep the wire under control.

That looks better than mine! I already had to Dremel the control case when I did a 7x12 to 7x16 conversion, so I might do some more surgery and mount the display w/o an external cable.

 

[eraserhd]

Alright, y'all. I have this lathe and I'd like to connect the tach to TouchDRO.

I haven't taken it apart yet but doesn't the fact that it can drive a tach display mean there's a point on the board somewhere with a nice square wave?

I know the motor is brushless, so it could totally be outputing the speed it's trying to drive, rather than a measured speed. But the funny thing is that when I've stalled the motor for a short bit, it spins faster to "catch up", so there's got to be an internal tach, right?

I might need to break out the oscilloscope. It's been collecting dust.

 

[ycroosh]

The motor most likely has an encoder disk that sends feedback to the BLDC driver (there are drivers that don't need an encoder, but they are expensive, so not likely the first choice for SIEG to use). If you are using a new-ish TouchDRO adapter, the tach input is 5V-tolerant. If you're lucky, you can just tap into one of the sensor output leads.

 

[ChazzC]

The motor most likely has an encoder disk that sends feedback to the BLDC driver (there are drivers that don't need an encoder, but they are expensive, so not likely the first choice for SIEG to use). If you are using a new-ish TouchDRO adapter, the tach input is 5V-tolerant. If you're lucky, you can just tap into one of the sensor output leads.

Based on my (limited) understanding of how brushless DC motors work and are controlled, it seems reasonable that you could tap into the output of one of the three Hall Effect sensors to get a pulse (well, a pulse every time a rotor magnet passes by). The processing of the Hall Effect data is processed inside the control box, so rather than looking at the outputs at the tachometer plug (which is what MacPod did), you need to look at the inputs to the controller (outputs from the Hall Effect Sensors inside the motor).

That said, and even though I have the equipment (including a nifty Bluetooth oscilloscope probe) to do so, I'm not inclined to go through the gymnastics required to get to the back of my Mini-Mill (or lathe); and there is limited easy access to the leads on the sensors themselves inside the motor cap. However, an adventurous soul, like my friend Bret or @eraserhd could try giving LMS a call and seeing if they would share the motor cable pinout details, which aren't labelled in their manual:

I assume one is +5V (maybe red), one is Ground (maybe black) and the other three are the Hall Effect Sensor outputs (the other three colors).