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Old 15th May 2006, 08:47 AM   #201
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Location: oslo
Default pulley

Quote:
Originally posted by Lord Dubious
Hi All

Regarding the pulley, my vote is for an aluminium flat pulley of 0.665" or 16.9 mm diameter to suit the width of a mylar tape belt. I believe this diameter will suit the controller design if the platter diameter is about 12" or 300 mm. I am not sure that a crowned pulley will allow the use of a mylar tape belt (something I was hoping to try). I hope that a flat pulley instead of a crowned pulley will satisfy those who use a rubber belt (or other type) to drive the platter. Hope my use of jargon is OK.

Perhaps it might be time to start listing some of the proposals to find out where this is going.

In brief, the following comments have been made (I paraphrase below, but with no intention of changing the meaning of each post).

JRags - voted for bronze pulley (actually meant brass as stated in later post) of 11 mm diameter with crown heights of 6 and 14 mm (to suit custom TT with sub platter). Later suggested that 17 mm may be best. Also stated that pulley diameter should be agreed by Mark and Vinyl-Addict.
john2 - voted for pulley to suit LP12.
Markqall - open to what everyone else decides.
Seth Hensel - seconds motion that pulley diameter should be agreed by Mark and Vinyl-Addict.
superhkm - seconds motion that pulley diameter should be agreed by Mark and Vinyl-Addict.
kevinchampion - happy to accept one size fits all by consensus of the group.

It appears that Vinyl-Addict and DaveM are candidates to make the pulley.

Hope this helps us move in the right direction.

Mark, I will keep track of the votes if this helps.

Cheers

For what it's worth at this point, as I learn more I realize that a larger diameter pulley is optimal for me, or 27mm as I have a 320mm platter to run(1:12),
min. is 1:24 (right ?) giving me an absolute minimum of 13 1/3 mm , but bigger is better.
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Old 15th May 2006, 10:42 AM   #202
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Default Re: pulley

Quote:
Originally posted by superhkm

For what it's worth at this point, as I learn more I realize that a larger diameter pulley is optimal for me, or 27mm as I have a 320mm platter to run(1:12),
min. is 1:24 (right ?) giving me an absolute minimum of 13 1/3 mm , but bigger is better.
At 33,3 rpm your motor needs to spin at 400 rpm. Isn't this too slow for the metal bearings used in the maxon motor (191) to work correctly?
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Old 15th May 2006, 11:01 AM   #203
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Default Re: Re: pulley

Quote:
Originally posted by SisterOfMercy


At 33,3 rpm your motor needs to spin at 400 rpm. Isn't this too slow for the metal bearings used in the maxon motor (191) to work correctly?

Thanks for caring, frankly I have no idea, I just read this :


Quote:
Originally posted by Mark Kelly
For the 110191 motor with the 12V controller the pulley to platter step up ratio MUST NOT be greater than 24 : 1 if you wish to include 45rpm. The controller was not designed to run this motor at speeds greater than 1000 rpm - it can be made to do so but that requires changes to the circuit and the power supply which preclude battery power. It is easier to use a lower volage motor such as the 110189.

Your 11mm pulley will give a max platter diameter of 264mm at 24 : 1 - OK for subplatter drive but no good for platter drive. If you wish to use a pulley of this diameter buy the 110189 motor rather than the 110191.

In addition, the speed variation due to belt creep gets worse as the pulley diameter is reduced - ceteris paribus the belt creep increases with the step up ratio.

The step up ratio should probably not be less than 12 : 1, if you want to use a low ratio use the 226764 motor.


Looking at the 110191 spec, it seems with a no load speed of 6050rpm one would think 1:24 would be no problem at all, even for 45, ( 45x24=1080 ) But then again , Mark should know.
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Old 15th May 2006, 01:51 PM   #204
JRags is offline JRags  United States
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Default Pulley Diameter

Superhkm,

I'm no expert, but based on my calculations using a 16.9 mm pulley will give you a speed of 592, which corresponds pretty closely with Mark's comments on speed error in thread #3 as follows:

Quote:
if the 110191 is used at 600 RPM it improves to about 0.02%. As mentioned above at these levels belt creep becomes more important than motor variation.
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"Always Searching for Perfection"
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Old 15th May 2006, 02:07 PM   #205
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Default Re: Pulley Diameter

Quote:
Originally posted by JRags
Superhkm,

I'm no expert, but based on my calculations using a 16.9 mm pulley will give you a speed of 592, which corresponds pretty closely with Mark's comments on speed error in thread #3 as follows:


Splendid, I am confused but calm
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Old 16th May 2006, 01:04 AM   #206
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Default Where the numbers came from

Just to clear this up:

The controller is required to operate correctly on battery power, so it must be able to operate when the battery terminal voltage has dropped to 11.4 volts (the nominal end point of a discharge cycle for a 12V SLA). The constant current circuit on the high side and the current compensation circuit on the low side both eat about 1.1V, so we have a max of 9.2 V available to the motor. The no load speed constant of the 110191 motor is 121 rpm per volt. 9.2 x 121 = 1123 rpm and 1123 : 45 = 24.9 :1

BUT that's the no load speed, the controller requires some headroom for the current compensation to run, so 24 :1 is the absolute max ratio, I would prefer to see ratios below 20. The controller was designed to specifications from Vinyl Addict and the required speeds were 600 rpm and 810 rpm, a ratio of 18 :1.

The 110189 motor has a no load speed constant of ~180 rpm per volt so it will be happy up to say 30 :1.

The controller can be reconfigured to run on any supply voltage up to about 36 volts. At this level the max speed for the 110191 motor would be about 4000 rpm, for the 110189 would be about 6000 rpm.

I have not published the mods because I have not been asked for them and because above about 18: 1 the performance of the controller is compromised by belt creep. However I am not going to get in your way if you want to run higher speed. My recommendation would be to leave the controller as is and run the 110189 motor but if you want to know how to run the controller at higher voltage just ask.
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Old 16th May 2006, 02:22 AM   #207
DaveM is offline DaveM  United States
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Default Pulleys

So, I have a bit more info about how I could make the pulleys happen. I talked to the machinist at work and we looked at the shaft we are mating to (3mm~1.175"). We would start by center drilling the hole and them drilling it out. A reamer would then be run through to achieve a tight tolerance diameter. The diameter of the puley surface would then be turned. It makes no difference to the machine if it is curved or straight. From there the parts are cut off the bar stock. That should give us a runout tolerance of less than .001.

I can make these happen for beer money and material. The machine has not been busy lately and there is no reason I can't squeeze this into the regular shop schedule.

The only hangup I see is the drilling and tapping the setscrew holes. I have the tools to do that, but depending on the number of pulleys desired, I may not have the time. I am in the process of buying a house, selling a house, parenting a 2 year old and keeping a marriage together. Oh yeah, and then there are the projects...

DaveM
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Old 16th May 2006, 05:47 AM   #208
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Default Design Error

STOP PRESS - DESIGN ERROR

I have discovered a small problem in the circuit. While I was working out a simple way of calibrating the current compensation circuit I found that the Widlar current mirror on which the current compensation is based does not have a uniform multiplication ratio at low motor currents.

This is because the resistors in the emitter return paths of the transistors in the current mirror are fairly small so at the very low idle currents the 110191 motor pulls (around 1 mA at these speeds) the voltage drop is not large enough to swamp the emitter base voltages. Altogether this means that the multiplication ratio of the Widlar current mirror varies somewhat with total current.

A simple cure is to bypass the motor with a resistor which increases the current draw and pulls the current mirror into its linear region. A resistor of 1 k across the motor terminals improves things enormously.

Since A) the required value varies with motor used and B) I've already bought all the resistors, I propose that people add this resistor (if required) themselves. It might be interesting to try a carbon film as these have a negative tempco which might help balance the positive tempco of the motor coils.
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Old 16th May 2006, 06:40 AM   #209
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Default Re: Design Error

Quote:
Originally posted by Mark Kelly
STOP PRESS - DESIGN ERROR

I have discovered a small problem in the circuit. While I was working out a simple way of calibrating the current compensation circuit I found that the Widlar current mirror on which the current compensation is based does not have a uniform multiplication ratio at low motor currents.

This is because the resistors in the emitter return paths of the transistors in the current mirror are fairly small so at the very low idle currents the 110191 motor pulls (around 1 mA at these speeds) the voltage drop is not large enough to swamp the emitter base voltages. Altogether this means that the multiplication ratio of the Widlar current mirror varies somewhat with total current.

A simple cure is to bypass the motor with a resistor which increases the current draw and pulls the current mirror into its linear region. A resistor of 1 k across the motor terminals improves things enormously.

Since A) the required value varies with motor used and B) I've already bought all the resistors, I propose that people add this resistor (if required) themselves. It might be interesting to try a carbon film as these have a negative tempco which might help balance the positive tempco of the motor coils.
Do we have to make notes now, or will you add to the schematics ?
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Old 16th May 2006, 06:47 AM   #210
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I have now received payments for 18 motors and will make the order on the 18th.
Since the 17th is the Norwegian "National Day" no one works and I will therefore extend the time limit for orders to gmt 0700am may 18th.

GAgola , you have mail.
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