MESU Mount update and acceleration info request

paul K

Just a quick update and request for info.

Lucas Mesu has been extremely helpful with this problem. An initial skype with Lucas identified a broken motor drive shaft. I sent the motor back to Lucas and received it back all fixed and ready to reassemble. Reassembly was accomplshed with another Skype call today and once you know what to do, reassembly is pretty straitghforward. I wouldn't recommend trying to remove and reassemble a drive motor without information from Lucas. There are some key marks on the gear and torque is fairly critical. Having seen the inside a bit, I can confirm that these mounts are really high quality precision engineering. Mine has been great until the dec motor shaft problem, but support and service to fix it was first rate.

So onto the information request to Don, I am thinking to reduce the acceleration as I've got a big (ish) scope mounted - it's a celestron C14. So I guess I'll need to visit servoconfig to make a change. Any thoughts on what to change and by how much would be great. I guess the same applies to deceleration too.


Hi Paul, 

I'd have thought it would be more of a mount question, so as it's a Mesu maybe see what Lucas suggests?

Best wishes

Sent from my Galaxy

Don W

Hi Paul,

The acceleration loads can be reduced by setting the values for "Default Acceleration" in Servo Config on the Motors/Encoders tab of the Edit Parameters section.  The single value for this parameter controls both acceleration and deceleration.  Changing the value of the "dpsps" box to a lower number is what to do.

I don't know what the value is set for by Lucas on your Mesu Mount.  Values higher than 1.0 dpsps on both RA and Dec probably won't seem to be obvious to you.  Values set less than 1.0 (like 0.5 or less) will be noticeable and might make guiding sluggish.  But if you have a setting like 4.0 or greater, then reducing then a value reduction can have a significant reduction in the load with a large telescope.  A C-14 is big, but relatively short, so it's moment of inertia is a lot lower than say a 6 foot long refractor.

So try setting a lower number for "Default Acceleration" and then see if you can tell if it "slows down" your slews.
Don W

paul K

Thanks Don and Martin.

I'll have a look at the settings Don. It's a very good point about the moment of inertia. In a skype call yesterday, Lucas referred to a C14 as 'big' and that should've prompted me to ask about the acceleration values, but I was too engrossed in trying to start some small hex head bolts into the motor housing....:)

I'llprobably check with lucas as well to see if he has any mount specific thoughts on it.

I'll report back.

thanks for help,

Sedat Bilgebay

Hello Paul,

If you are an imager like me, fast slews and high acceleration shouldn't be that important for you. On an average night, my mount slews long distances only once or twice so the lack of speed doesn't bother me at all.

As explained earlier, the accuracy of the initial slew followed by a high precision centering in max 2 attemps is very rewarding and time saving. 

Let me share a screen shot of the initial settings Lucas prepared for me first...

Here the slew speed is 6 degrees per second and default acceleration is 2 dpsps. I reduced the slew speed to 1 dps and the accelaration down to 0.3 (which seems to be the minimum) and have been using the mount for the last 3-4 years without any ill effects on the performance or the health of the mount. Hope these help.

Meanwhile, the drive shaft is working at 2000:1 reduction. The motor was able to drive my very heavy setup even when the drive shaft was fully disconnected thanks to the friction due to the applied pressure against the drive disc. So I dont think your problem is caused by carrying a C14 on the mount. After all the mount is declared to be capable of carrying 100 kgs of payload excluding the counterweights. 

paul K

Thanks Sedat, I'll try to slow things down a bit to reduce stress. It may be a good thing to do and Lucas has said it won't cause any harm. I'm an imager too, so speed of slews isn't a big deal, but guiding accuracy is of course.

It's interesting what you said about high precision centreing. I use SGP to manage my sessions and when I use Platesolve 2, centreing is accomplished in max 2 iterations. Sometimes I use ASTAP for platesolving and that usually takes about 5 iterations. I switch between the two sometimes as there are cases where PS2 won't solve and ASTAP will and vice versa. I would like to use Platesolve 3 with SGP, but it can't currently be integrated.

When I try reducing accel and slew speed, I'll see if it makes any difference to the number of platesolve iterations.

It's all a bit academic at present for me here in the UK, as the last few years have been mainly cloudy between September and April, perhaps it might change for the better, let's hope so.

thanks for sharing,