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Motor size and capacity and performance......

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#1 mistyridge

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Posted 08 April 2011 - 01:54 AM

It seems to me that the capacity and performace of the medium cost mounts on the market in the last six to seven years could be improved if the stepper or servo motors were larger and more robust. If they are even a little off balance the motors sound as though they are about to burn out or stall. The cost of heavy duty motors can't be that much. What do you think.

#2 Lightning

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Posted 08 April 2011 - 03:46 AM

I think a lot of the mass-market mounts used to use plastic reduction gears too that would fall apart after several years.

#3 rmollise

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Posted 08 April 2011 - 04:56 AM

I think a lot of the mass-market mounts used to use plastic reduction gears too that would fall apart after several years.


Which mounts are you talking about? The LXD 75 and CG5 don't. Even if they did, they wouldn't "fall apart" in a few years.

#4 rmollise

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Posted 08 April 2011 - 04:58 AM

What do I think? Not really. Large® motors are not needed in this application. And it's rarely the motors that give problems with go-to mounts...and when they do it's highly unlikely they will burn out. In this application there is no need for high and constant torque, and the motors can last a long time.

Look at the size of the Hale telescope's motors vice the size of its mount. ;)

#5 David Pavlich

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Posted 08 April 2011 - 08:01 AM

I agree with Rod. When a mount is used as it's supposed to be used, within the prescribed weight limit and BALANCED, the motors will last a long time. Also, even the low cost mounts like my LXD75 is equipped with metal gears.

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#6 jmiele

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Posted 08 April 2011 - 08:08 AM

agree. with a properly balanced setup the motors are using very little force. length of service goes back more to the quality of the bearings. and even then some of the old meade LX stuff had those white plastic bushing and served well for mant years. FWIW.. Joe

#7 Eddgie

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Posted 08 April 2011 - 08:21 AM

Electric motors produce full torque at 0 RPMs, so there is a lot of power even in a very small motor.

The torque is magnified many many hundreds of times by the gear box built into many of them, and another 180 to 300 times by the worm gear.

When a motor strains due to out of balance, we hear it, but that doesn't mean that there is a problem. It just means that the motor is working harder than it needs to because of unbalance or drag (or both).

Putting a bigger motor means it would strain less, but it also means that it would draw more power in normal (balanced) operation than would be necessary.

This is not a problem if you run it from a 110 Vac power source, but a very large percentage of people want to run their scopes off of a car battery or power pack. This makes it far more desirable to use as small a motor as necessary for the task, but the compromise is that the operator should keep the balance close to minimize the current draw.

So, there is always a tradeoff. Most of the time, I personally run off of a 3 amp supply and I can run two Go-to mounts with no problem as long as they are not slewing at the same time (GCE and Meade LXD-750 which uses a TINY motor for such a giant mount). So for me, the motors are fine, and I like being able to run the both without needing a bigger power supply.

Everything that engineers do is a compromise. Your requirement for bigger motors may not sit well with the majority of users requirements to keep power consumption as minimal as possible.

#8 jbattleson

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Posted 08 April 2011 - 04:12 PM

Most of what you hear when a mount is working hard is gear noise. A larger motor wouldn't change that. IMHO
John

#9 mistyridge

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Posted 08 April 2011 - 04:52 PM

Hmmm, good point about battery life and big motors. All the Celestron mounts I have owned never had a motor failure but sure sound like they have problems. Noisy gear trains and sound board like housings may be the reason. I have had failures in the HC and electronics in all cases. This seems to be their weak point. It is also the hardest problem to diagnose, and one the end user cannot easily fix.

#10 Kaizu

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Posted 09 April 2011 - 01:46 AM

Few years ago I built new motors and control system for an old Lomo ATZ-telescope. The old 80W sleving motors stalled if the system was unbalanced about my weight (100kg). I changed them to 360W (RA) and 180W (DEC). Now the mount turns if the system is balanced better than 300kg. I have once lifted the roof of the observatory, I adjusted the inverters and forgot to open it. Even the small 10Ncm tracking stepper can lift the roof (also tested). The gear ratio is so big that torque at the end of RA shaft is ca.2000Nm. There is not sliding couplings.
Instead of high power you can use torque and time to destroy things.

Kaizu






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