TMC2100 How hot?

Chris Vaughan

I've put together the v1.27 miniPCB with TMC 2100s. I've got CFG1/2/3 at GND/open/open for 16 microstep spreadCycle mode. I'm using polulo 1209 stepper motors (2.7V 1A). Just waiting on some pulleys to put it on an EQ5. All is working well, connecting via bluetooth with the android APP and skysafari.

My question is, how hot should the TMC2100s get ?
They are getting very hot after 10-15min. So hot that I can't touch the heatsink on the TMC2100s for more than a few secs. This was with Vref set to 1V (which I'm sure is what a 1A stepper should be set to on the TMC2100). I dropped Vref to 0.7V and its still hot. This was with it running on a 12V supply, but just got a 12-24V converter and its still hot (with Vref at 0.7 - 1V). The stepper motors get warm but not hot. If I drop Vref too much (e.g. down to 0.5V) then it stalls at any GOTO speed above 1deg/sec.

Is this how it is? Mind you, ambient temp was about 28C at night when I tested it. Sydney was the hottest place on the planet yesterday!!

Cheers Chris

Re: brand new to this stuff, need starting advice


I just ordered a bunch of parts. Teensy 3.2, TMC 2100 drivers because the 2130 are out of stock everywhere, wifi, 20 teeth and 40 teeth pulleys (6.0mm they are coming from China so....that will be a while), Nema 17 motors, and an electronics kit since I have nothing. PLus some other parts like the power jack etc. 
At 52 YO, I guess I can learn electronics :) 
I did take apart the whole mount and clean it, re grease, polish etc. I needed to use two hands to turn the RA before this, it was bad. I'll take apart again and use better grease before final upgrade. 
I will be back in a few days when I realize I have no idea where to start!! 
Luckily, I also have access to a very good high school that has a robotics program. Those smart teenagers will help me :) 

Re: brand new to this stuff, need starting advice

Mark Christensen

Issues like periodic and non-periodic error are why you either:

0. Clean and adjust the mount
1. Use PEC
2. or Guide

Cleaning/Adjusting/Guiding is the simplest and most robust solution, in my opinion, with guiding being essential as it compensates for all kinds of errors and effects outside of the mount. Even with focal lengths like 300mm.

But not for planetary imaging. For that the TMC chips with 256 point interpolation (between the microstep pulses) are better than the others - it will give you smoother short term (like a video frame rates) motion.

Your CG-5 has, I believe, a 10 minute RA worm period. That means one worm rotation is 600*15 =9000 arc seconds (at DEC=0). So even 32 microsteps (without interpolation) would result in (with direct coupling) 9000/(32*400) = 0.7 " per microstep, which you will (believe me) see in planetary video. And if you have to run at 16 microsteps per step it is 1.4" per microstep without interpolation. But the interpolation will give you 8X improvement, or 0.088" per increment, which you will never see.

Finally, if you must, must use 1/4" bore pulleys (aka 6.35mm), then you can get bushings. But as Khalid pointed out, there are plenty of 6mm pulleys out there.

Pulleys have an advantage (esp for the CG-5 type mounts) because you can then tuck the motor under the axis, whereas direct coupling means it will be sticking out and may unnecessarily limit motion. Using a reduction will give smoother short term motion (which is what you care about for video) no matter what you do. It will, of course, then limit your max slew speed and you have to run the numbers to decide how much you care.

It sounds like your intended use has little to do with GOTO, focusers, Bluetooth, and all that, by the way. If you haven't done it you might want to clean and adjust your mount - I've never seen a CG-5/LDX-75 class mount whose tracking and response to guiding didn't benefit from doing that. There are several websites with How-To info on that (Google "AstronomyBoy", for example).

Mark Christensen

On Sun, 1/7/18, Khalid Baheyeldin <kbahey@...> wrote:

Subject: Re: [onstep] brand new to this stuff, need starting advice
Date: Sunday, January 7, 2018, 6:41 PM

You can get pulleys in
6mm bore.

The reprap stuff
for 3D printers made this stuff readily available on


Search on  "GT2

The issue is
that with any transfer mechanism, be they gears or pulleys,
you can introduce non-periodic error.

See the small pulley in this video at 5:50

That wobble will introduce
elongated stars.

Re: OnStep Configuration Generator


A config program is a good idea but care needs to be taken that more time is not spent updating the config program than you spend enhancing the core code.  That said, what I read in here is than many people would like to upgrade older telescopes goto but are either unable to deal with soldering or they, like me, are more than a bit scared of even the configxxx.h file.  At first, I had absolutely no idea what the variables did.  I read, I asked, and, as you know, I made mistaiks (oops).  However, my stumbling around eventually bred some understanding and now it works although I still don;t understand exactly why.

I printed the configxxx.h file and read it like a newspaper over and over until I got my head around the logic.  It was hard to understand, even from the comments, how to configure my device.  Perhaps more comprehensive commenting (instead of a user manual) would help more.  "This variable changes xxx so that yyy may go faster, slower, whatever."  A real dummies, simple guide.  

Maybe that would help.  The problem is, YOU know exactly what each one does.  I and maybe others do not.  I have found the best way for me to be sure that I understand something is to explain it to someone else.  I discover this when explaining things to my son when he was about 7.  I could explain things simply and concisely only if I fully understood it myself.  

The lack soldering skill is a problem as is sourcing probably unfamiliar components.  I wonder if EasyEDA could supply fully populated PCBs perhaps without the Teensy.  I know Seeed Studio do this but in runs of (I think) 10+ boards.  This minimum quantity might put you and/or Howard into selling finished boards.  Selling working boards would certainly increase your numbers but, warranty and support would probably be a nightmare for you.

The above is just me thinking and writing at the same time.  Two things at once is never a good idea for me...

Re: Port of OnStep Alpha to STM32F103 ARM Cortex M3

Khalid Baheyeldin

An update on STM32F407 ...

The Arduino_STM32 team added support for HardWaretimer.h to the above chip.

So, it is only missing the EEPROM emulation in flash, then it can work with OnStep.

Once that is done, we can add support for it, and then will have a 168MHz ARM Cortex M4 processor that can be bought for as low as $9 on eBay.

Re: brand new to this stuff, need starting advice


that looks awful! Hopefully with short subs less than 2 minutes wide field stars won't look too bad.
I was hoping not to have to order from China but I guess that how it has to be. Thanks! 

Re: brand new to this stuff, need starting advice

Khalid Baheyeldin

You can get pulleys in 6mm bore.

The reprap stuff for 3D printers made this stuff readily available on eBay.


Search on  "GT2 pulley".

The issue is that with any transfer mechanism, be they gears or pulleys, you can introduce non-periodic error.

See the small pulley in this video at 5:50

That wobble will introduce elongated stars.

NMEA GPS via USB B port


My MiniPCB has a USB type B connector and I was wondering if I can connect a serial GPS device that outputs standard NMEA serial data to it.  Is this possible?  Is it likely to be possible?  I am not bothered, just askin' since I already have the device.

Re: OnStep Software Development

Khalid Baheyeldin

It was compiling yesterday for me. So was surprised it doesn't. Thought it was in the IDE's libraries or something.

Anyway, it is good now.

Take a look at the pull request I just created. Makes the 24C generic and not tied to any platform.

Minor tidying up for code portability and reuse.

Re: brand new to this stuff, need starting advice


the shaft on the mount is 6mm. 

Re: OnStep Software Development

Howard Dutton

The DUE support is for play right now, I fully expect it to not work.

I changed the 24LC256 library to read() instead.  That worked too in my testing (on the Teensy3.5,) I don't have a DUE but will order one for testing.

Also... I looked briefly at the RAMPS and DUE thing a while back and recall that not just any RAMPS1.4 shield will work.  It needs to be designed for the DUE.

Re: brand new to this stuff, need starting advice

Khalid Baheyeldin

Haven't tried that myself, but you can use a coupler?

Re: brand new to this stuff, need starting advice


Oh I just measured the shaft on the CG5 and it is 6mm not 5mm. I see lots of 6.35mm bore pulleys, will this be too loose?? 

Re: brand new to this stuff, need starting advice


My 300mm lens and D5300 get me 5.478 arcsec/pixel according to astrobin. The worm gear is 144 teeth. 
I could go with a higher torque motor rated at 2 amps rather than the .4 amp one. It's not like I am going to be slewing around all night. Just to one target then tracking after that. 
TBH I just want a working mount and fancy the idea of DIY. I have built all my own scopes but never have done electronics. I am hoping to have this done for Jupiter prime time with my 6" Newt. and USB camera. 

Re: OnStep Software Development

Khalid Baheyeldin


I am getting this error when compiling for RAMPS/Due.

Other platforms are fine.

In file included from sketch/src/HAL/HAL_Due/HAL_Due.h:11:0,
                 from sketch/src/HAL/HAL.h:52,
                 from [something]/OnStep/OnStep/OnStep.ino:46:
sketch/src/HAL/HAL_Due/../drivers/HAL_24LC256.h: In member function 'uint8_t _eeprom::read(uint16_t)':
sketch/src/HAL/HAL_Due/../drivers/HAL_24LC256.h:58:20: error: 'class TwoWire' has no member named 'receive'
     result = PWire.receive();
exit status 1

Re: brand new to this stuff, need starting advice

Khalid Baheyeldin

I can speak a bit about the CG5, since I had one for some time.

It was GOTO with the iOptron GotoNova 8400 kit.
That kit was supposed to have PEC, but it never worked for me.

Even without PEC, I was able to do unguided exposures of 45 seconds @ 1280 mm focal length (C8 with 0.63X reducer). Occasionally I would be able to do 60 seconds, or 90 seconds, depending on where the worm gear was. When it was changing directions in its sine wave curve it would change the least.

If you want sample pictures I took, I can point you to them.

One of the reasons I am exploring OnStep is to get PEC working. But things changed and I came across a Vixen GPDX with Vixen's Sky Sensor 2000 PC, and its PEC does work and I am able to do 120 seconds unguided. But that is due to more precision by Vixen in their gears. Will still build and OnStep, but it is less urgent. The parts are ordered (from prebuilt parts, since like you, I don't want to do deep electronics soldering stuff).

You said you will be using wide field. So the focal length will be less than 1280mm. Perhaps 600 mm or 400 mm, or even less. That means you can do more exposures than 45 seconds. Perhaps 60, 90 or 120 seconds.

Your camera is also a factor. Find out the sensor's data, and go here

And you will be able to know how many arc/seconds per pixel you will have. The more arc seconds you cram in a pixel, the longer the exposures you can take, and the more you can away with imprecise gears/pulleys.

OnStep's PEC should help, but it is not the be-all-end-all solution because of secondary non-periodic error in the gears/pulleys between the motor and the worm gear. Unless you connect the motor directly to the worm gear, like Howard and other Losmandy G11 owners do.

Re: brand new to this stuff, need starting advice


Thanks. I read the WiKi page many times and need to actually have some hands on now to get any more out of it. 
I have seen some pictures of mounts (google) and looks like 10/40 teeth pulleys so 4-1 but I am having a hard time finding 10 teeth pulleys . So I might end up with 20/40 or 2-1. Does that mean I will need MORE torque? 
 What do you think about Bluetooth vs WiFi? 

Re: OCS question


Thanks for your SIM800L support !
If you can get some help it is a very good thing ! So thank you Khalid as well.

Talking about OCS, your stellarjourney site and your OCS program are very informative but i'm looking for a schematic to get a clearer view on the wiring of relays and sensors.
If you have any file, i would be interested with it.


Re: brand new to this stuff, need starting advice

Howard Dutton

I can't make any statements about what the unguided performance of your mount will be (factors beyond OnStep's control.)

The MiniPCB makes a great little basic telescope mount controller if it has the features you want and you are comfortable building it.  They are what I use.  If building a MiniPCB use the TMC2130 stepper driver (the real Watterott OEM ones if possible.)  It has 3D printable case designs too.

A Ramps1.4/Mega2560 controller, for example, is easier to put together and costs less.  It also has limitations and hassles "overall" compared to the MiniPCB.

Read the WiKi sections on the various controllers if you haven't done so already.

I'm sure other coaxial DC power jacks will fit the MiniPCB.

The if given a choice I'd wait to figure out the overall gear ratio before selecting a stepper motor (so we can pick one tailored to the design.)

As for what pulleys will fit hopefully someone who's been down this road will speakup.  There are many CG5 class mount's with OnStep but I've yet to get exact specifics on transfer pulleys/gears for a NEMA14 or NEMA17 stepper based design.

Re: brand new to this stuff, need starting advice


Keep asking questions.  I too am new here.  I just finished my goto Dob project -- today.  Look at this topic,,,20,0,0,0::recentpostdate%2Fsticky,,,20,2,0,7689661.  There are lots of side tracks and I ask some pretty stupid questions.  However it now works and once the temerature warms up a bit so that my 72 year old bones can stand being outside I shall see if it does what I think it will and track stars. 

There's a Google photo album of my build, complete with some of the false starts.  There is also a very bad video from today of my scope actually moving.

I have a lifetime of electronics experience and just about none in astronomy.  Can't have everything, right?