Help with electronics upgrade

[jim_mcmillan]

Hi Mike,
I'm afraid we sort of hijacked Rick's thread, and may be guilty of "information overload"... Sorry Rick.
Anyhow, since we've gone this far, why stop now?
So I looked for info on the A6497-9412KTG motors that Rick said he has on his bot. The Oriental Motor site didn't have anything about it online, but a Google search turned up a reference to it on CNC Zone. It was described as "2 Phase, 1 Amp, 4.39 ohm". That is second-hand info, and it conflicts with Mikes info so I'm not sure what to believe. At any rate, it doesn't really matter that much. the Geckos won't complain either way. Just make sure you install the right current-set resistors per the Gecko manual else you risk overheating the motors.
The bottom line as far as I can figure is that that toroid is probably way bigger than needed, which is fine, and the voltage should fall in the mid to high 60s after rectification and filtering, which should also be fine with a comfortable margin. Just put a 5000 to 10000 uF electrolytic cap with a voltage rating of at least 100V across the rectifier output, and the power supply is ready to rock.
Jim

PS. Mike, that first line in your last posing is confusing me a bit. Wouldn't half coil give you half the inductance rather than 1/4 as you stated, or did I misunderstand your meaning?

[Brady Watson]

I feel a lot of "mechanical vibration" when my machine moves in x and y axis. If I Put my hand on the Y carriage, I can fell it "Mechanically shake" during all types of movements.

Don't read if you have a PRS...This applies to PRTs only

Regardless of what electronics, motors and software you use to drive your PRT iron, there are still a few maintenance issues that you'll want to tackle ASAP.

Pinions and racks should have grease on them. Don't slather the grease, just keep them wet. When your cut quality degrades, it is telling you that you need to do maintenance. The following 3 areas may need attention:

1) Pinions - PRTs with A6497-9412KTG (3.6:1 motors) should have 25T pinions to run correctly. 16s, 18s & 20s wear very quickly & only have one or two teeth at most engaged in the rack, which makes them wear faster & exhibit cogging tendencies. When you order pinions (cheap) order 2 sets. Compare your old ones to new ones. Also, the proper tension on a PRT motor turnbuckle is 3.5 turns after the spring just gets tension. Any more & you'll prematurely wear out pinions - too lose & you'll skip teeth.

2) Matted down/forged & dirty rails where the v-roller bearings have worn a groove into the angle rails. Dress the rails with a file and sandpaper or scotch pad. This makes an unbelievable difference if you have not been maintaining them. Closely look at the rails - carefully run your hand over them - any little sharp edges or bumps you feel act like boulders when v-rollers hit them. Clean 'em up & maintain them with a brown 3M scotch pad.

3) V-roller bearing adjustments on Z axis/t-rail as well as lower bearings (side to side) on Y car. You should get in the habit of grabbing each axis with power on & no movement - and shake the heck out of it. Look, listen and adjust.

If you are going to add more power or speed to this down the line, there are a few things you will NEED to beef up. If running 3/8" Boston gear rack there isn't enough meat to support higher loads & speeds. You'll want to bump up to a 1/2" Browning rack & suitable 1/2" wide pinions to match. You'll want to machine yourself some 1/4 or 3/8" X & Y motor mounting plates out of AL or steel IF you have the single 1.5" angle iron motor mount with little 3/4" angle spring perch on them. They are way too flimsy for speeds over 4 IPS. You'll want to gusset the table like a late PRT or PRS tool. And last, but certainly not least, you should toss the gold utility strut on the gantry & replace with 1.5 X 2.5" box steel. Weld it to the 3X3s and also tack the Y rails to the 3X3s on each end of the X car. You'll never rack the gantry again...

-B

[richards]

I follow closely several different forums, each one hosted by the manufacturer of a CNC machine. When I'm posting to those different forums, I like to think that cross-talk between forums might cause some hurt feelings. Each design has good points and each might have some weaknesses, but Shopbot is a great company with a very good machine. It's not perfect just as none of the other machines that I follow are perfect, but I try not to compare features or to list limitations when visiting the various forums.

Sometimes sending a private e-mail would be the better way to help.

[richards]

Gene,

I think that you would agree that that post was in direct response to a question from someone who wanted to mix and match electronics from his Shopbot onto another type of machine. I think that you would also agree that I cautioned him about using older Shopbot electronics with known issues when other options were available.

I've done the same thing here, on the Shopbot site. When 'botters have asked about the feasibility of using Mach 3 and hardware designed for Mach 3 on their Shopbots, I have tried to point out that they would lose compatibility with Shopbot software, which is one of the main reasons that people buy a Shopbot.

When people ask a direct question, i.e., when they mention the competition, I give a direct answer. I try to be as fair-handed as possible while giving factual information. Sometimes my responses might be taken as being 'unkind', but they're not meant to be unkind.

Have you noticed that each of the 'faults' that I listed in that post have been corrected in the latest Shopbot controllers? Like any good company, Shopbot pays attention to complaints and concerns and eliminates the problems whenever possible.

The Shopbot PRS models are FAR superior to older models. The PRT-Alpha that I owned was FAR superior to the models that came before it. Each generation is better. Each generation of software is better. Each generation of electronics is better. Each machine, Shopbot or competitor, was designed to fill a niche. Shopbot has continued to improve their mechanical designs. Some of the designs of other manufacturers have remained static, without any substantial changes.

Personally, if I were building my own machine, I would model it after the PRS. (I would drop the side rails to table-top height and I would use linear rails and trucks rather than V-rollers, but other than that, I really like the basic design of the machine.) Of course, given my age, and my general health, I will never build my own machine.

[richards]

Sometimes change is beneficial.

I don't have all the facts about the original PR and PRT machines, particularly facts about the stepper drivers used in those machines; however, before Gecko, it was common to use stepper drivers that used full steps (200 steps per shaft rotation) or half-steps (400 steps per shaft rotation). Gecko's stepper drivers have 2,000 steps per shaft revolution.

However, from the unit values Rick posted, assuming that he has motors with 3.6:1 gearboxes, it appears that he has a machine that has stepper drivers that produce 800 steps per motor revolution. It also appears that if the motors are geared 3.6:1, that he has 25-tooth pinions on the on the X and Y axes,and a 20-tooth pinion on the Z-axis.

Changing to Gecko stepper drivers would give 2.5X better resolution (smaller distance moved per step).

The unit values would become 1833.4649 for the X and Y axes and 2291.8312 for the Z-axis.

[RickWyatt]

Thanks to everyone again! I am very luck to have so many supportive people here to help.

There were some difficulties with the site last evening and I replied to Mike via email. I will post my reply here so that others could follow the conversation for help as well:

Mike,

Wow! Thank you!

This community is amazing. I hope to be able to contribute back as soon as possible. I think documenting this process and putting it all in one place will be a great start.

Thanks too for the g-code warning. However, I would prefer g-code. I was a part of the exhibit and display industry for 14 years drawing,programming and running Komo and AXYZ machines. So, I am actually lost looking at the Shopbot code. I recently stepped out on my own and have my Shopbot and a 30watt laser from Universal. I am capturing a niche' area of the exhibit and display industry that seemed to be missing.

As far as the toroidal transformer goes, I'll have to figure out the VAC somehow. It does have a bridge rectifier on it that is marked 600v.

On the G201's: they came with a resistor in positions 11 &12 as you said. One of the drives came with 2 resistors in those positions. Not sure why? But I can check the resistance on those to be sure.

I figured those 201's were older. I will probably still use them just to keep costs down.

Although I don't have a lot experience with the electronics, I think by learning the how's and why's will help me to produce the best parts possible on this machine. Not to mention, less down time when something goes wrong.

Thanks again, MIke, I sincerely do appreciate the detailed help. I hope I could return the gesture in some way. Please feel free to let me know if you need anything.

Rick Wyatt

[RickWyatt]

use 18 tooth pinions...a cheap way to go and will help but you will loose speed.

you start upgrading your speeds then the mechanical problems will rear their head...then you want to upgrade that...then another upgrade then another....that is how the mechmate was born.

Gene,

You mention, yet, something else I need to learn about. I will look at my documentation I received with the machine when I get back to the shop on Monday. I will count the teeth on my rack and pinion to post here along with my gear box ratio.

Rick