Info Wanted - Basics of DC Motor Conversion w/ Controller

Can anyone point me to a web resource that lays out the basics of DC motor controlling or possibly put down the bullet points of same?
I would like to convert my drill press to DC and after reviewing the myriad of options on ePay, decided I need experienced help.
I would like to buy surplus/used parts if at all possible and need some guildlines as to what to look for such as DC field voltage of motor, typical controller types used, pitfalls, etc.
If anyone could comment on what they did when they converted their machine(s) it would be greatly appreciated.
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wrote:

If/when you learn anything, please let me know, I am very interested in converting a DP to DC.
i
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DC motors work very well on DP's. The size of the DP, whether is has single or double pulley reduction and the material you want to drill normally are all considerations. If it's a large DP, then I'd go with something like Surplus Centers GE 1.25hp 104VDC motor. I have one on an old Hercules DP that was used to drill 1.5" holes in tool steel. With a small DP, a .25 or .50 hp motor might be plenty. With double belt reduction (center step down/up pulley) Smaller hp will do more. If you're old school, you can use a Variac and a bridge rectifier to run it. You will be adjusting while running when drilling because you're varying current and voltage at the same time. For better results, go to a solid state controller (KB, Minaric, etc.) and your spindle will maintain speed under load as current is maintained and voltage (pulse width) is varied (simplistic description). Some controllers have integrated reverse switching either by switches, relays or regenerative circuits. This is helpful/required if tapping. With the Variac supply, a reversing switch can easily be installed. The same with the solid state type, but they are a bit more sensitive to reverse surges (reversing motor while at speed). In most cases, one should stop the spindle before reversing direction. The regenerative type is the exception. A resistor can be used to apply braking for more effecient control. BTW, beware of small motors with high rated hp as this sometimes refers to "developed hp" due to high speed. Mass is usually a good thing. Basically, the above refers to PM (permanent magnet) motors. Shunt wound motors are effectively similar, but with a required field power supply needed. Most solid state controllers have this available at full or half supply voltage. A Variac can be tapped at the correct point for this. With two Variac supplies, interesting results can be had by varying the field supply. This method was used on old DC systems, ie. Monarch EE. The higher field voltage suppresses motor rpm but can add torque at low speeds. Very low field voltage can/will result in VERY high motor speeds and possible shrapnel. Respectfully, Ron Moore
wrote:

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Thanks Ron. I will see deeper into this, it is on my list of nice things to do when I get done with other stuff. Sounds very interesting. The motor on my Chinese drill press does not have any nameplate on it at all, so it is hard to match NEMA frame. Not an insurmountable difficulty, though.
i
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On 12 Feb 2006 07:56:53 -0800, "mechanized_robot"

First you need to understand the motors themselves.
http://www.electricmotors.machinedesign.com /
There is a ton of motor control stuff at http://www.microchip.com/stellent/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId 83&pageIdd
This is primarily aimed at use of Microcontrollers for motor control, but theres some good basic stuff, like drive cctry, there as well.

Just look for motors that have the speed, torque and/or power you think you need. Matters of field voltage (if not PM motors) can be dealt with. Understand that DC motors do have a maximum torque limited by max current. Reducing speed with pulleys or gears also increases delivered torque, but if speed control is done electrically then the motor must deliver the full load torque even at reduced. speeds.
Best speed control is obtained with tachometer feedback. Some motors have built-in tachs. An external tach or encoder can also be used.

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not to forget ST with their nice little 30A 40V full H-bridges.
Nick
--
Motor Modelle // Engine Models
http://www.motor-manufaktur.de
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Many thanks to Ron & Don!
This is exactly the primer I was looking for.
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I installed a surplus center DC treadmill motor and controler on my drill press about 5 years ago and it is a wonderful thing :) Thanks to Don and others for help with modifying the controler to work better as a tool motor. The treadmill controller had a slow ramp up and would only start at zero and you had to bring the speed up with a pot. This motor is no longer available from surplus center but it is rated at 2HP. The controler limits the current to 10 Amps so the actual HP is much less ~3/4hp. It is a series wound motor with a tach feedback to the control to maintain the set speed under variable loads. It has a max of 6KRPM and I set it on the slowest belt speed on the drillpress. I get very useful power from about 100 to 1000 spindle RPM without moving belts. The motor is biased (brushes offset) to run in one direction but is reversable and seems to do ok with that at slightly reduced power if you only use the reverse occasionally. You should be able to source a motor and controler from a used treadmill. I put one on the drill press, one on a 6"Atlas and one on a wood lathe. All are still quite happy. HTH Glenn

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wrote:

They're still around, though. I see them at Ax Man Surplus in Fridley, MN. http://www.ax-man.com /
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Glenn wrote: ... You should

"Buyer beware". Not all treadmill motors are equal. I have scavenged a few from the dump and one in particular was very surprising in its performance: with it running at full speed (6K rpm), I was able to bring it to a stop by putting my bare hand on the 10" flywheel!! This was supposedly a 1 1/2 hp (+-) motor. Yeah, right. I was very glad that I hadn't paid anything for it, or had invested any time installing it on a machine. POS for sure.
Bob
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    --If you're lucky enough to live in the SF Bay Area the Crucible has just released the schedule of Spring classes. Included is one on how to build a DC power supply. I'll bet they could tell you a bunch about the right stuff you'll need to do the job right..
--
"Steamboat Ed" Haas : Woohoo! Cheney sez
Hacking the Trailing Edge! : lawyer season's open!
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