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Help Needed: Trying to find the right motor.

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BioDieselDub

New Member
Hello everyone,

I am new to this group, and this is my first post. I searched through past threads to try and find an answer to my problem, but came up dry. It seems that the more digging I do online, the more confused I get. I am not an engineer, but I am 4+ years into prototype testing a machine I have invented. My current prototype is powered by a Rex Engineering 50 in-lbs Single-Phase Subfractional-hp AC Gearmotor running at 1RPM, purchased from McMaster Carr http://shorterlink.com/?DDUK2N for $44.55. So far this motor has run for a couple years, almost non-stop, without any problems. The motor speed is further reduced through a 60:1 worm gear to produce a final speed of 1RPH. I'm not sure if this motor is complete overkill for this application, but it barely strains at all even when the machine is under full load, so I figure I guessed the right torque. My new prototype needs to be adjustable speed from 1RPH to 30RPH without losing the required torque. The input voltage is regular house current of 110VAC. My questions/concerns are as follows;

  • Do I need a DC motor or can I get away with AC somehow? Cost is a factor, as I hope to build these machines for retail sale one day. I don't think I can get enough torque through this speed range using an AC motor.
  • Assuming I need a DC motor, what type do I need considering that this machine will run almost continuously? I want to go with a maintenance free motor that will last a long time, without costing a fortune.
  • Do I need PWM for speed control or can I just adjust the voltage?
  • How much noise will be produced from the motor and/or speed control? I need to keep the noise level at a minimum.
  • I am considering using automotive wiper motors for this application, but I don't know enough about them yet. They seem to be able to put out a tremendous abount of torque at about 40RPM. I do not know if they can be slowed down to the speed range I am looking for without losing all the torque, or if they will last long enough when used continuously (just had to replace one in the wife's 2004 GMC Envoy today as a matter of fact). I do like the fact that they are easily attainable (assuming I pick one from a popular car), and relatively cheap.
  • Any parts that I incorporate into this machine need to be available in large quantities, assuming that I will be in production one day (soon I hope). They also need to be available in Canada. McMaster will no longer ship to Canada, but Grainger has a location close by.
  • I would prefer do deal with Canadian companies where ever possible, American second, and Chinese at the bottom of the list. I strongly believe in supporting domestic companies, even if they are not the cheapest.
  • Grainger carries some Dart DC speed controls in the $50-$120 range. Not sure if I can get any of these to do the job. The price is right, but the max amps seem pretty low.
I don't think I am forgeting anything. This is a good start at least. I hope someone can point me in the right direction.

Thank you in advance for your time. :D

d
 

stevez

Active Member
Some motors can develop a lot of torque across a range of speeds - some cannot. It might be helpful to understand the torque requirements across your range of expected speeds. You would then compare the torque requirements to the available torques. Don't forget to consider the heating of the motor as well. A bad combination of requirements might be high torque demand at low speed for long periods of time - bad in the sense that it's rather tough on a motor.
 

redserpentone

New Member
biodieseldub:

motors from photocopier machines have great torque and in wide viriety of types: ac, dc, stepping motors..
wherre do you get them? Dumpsters
Canon, Panasonic and Kodak were built with absolutelly great parts.
Happy hunting :D
 

BioDieselDub

New Member
Hi Stevez,

I am going to try and find a 0-50in-lb torque wrench on eBay, and measure the torque at the worm shaft of the machine. From what I can see so far, it looks like 1-30RPM is too much to ask of a motor that needs torque across the range, unless i want to spend a pile of cash on a drive. I can probably get away with 1-10RPM if I need to. I'll have to get a better idea of the torque needed. With my machine fully loaded I can easily turn the worm shaft with my thumb and fore finger, so there is not a lot of torque needed.

d

stevez said:
Some motors can develop a lot of torque across a range of speeds - some cannot. It might be helpful to understand the torque requirements across your range of expected speeds. You would then compare the torque requirements to the available torques. Don't forget to consider the heating of the motor as well. A bad combination of requirements might be high torque demand at low speed for long periods of time - bad in the sense that it's rather tough on a motor.
 
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