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Les Newell
Hi Nathan,
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I went the cheapskate route and bought some treadmill motors from Surplus Center. They were similar to these: <>. Mine have a short shaft sticking out the back, perfect for an encoder. You would have to ask to find out if these motors also have a shaft sticking out the back. Surprisingly for a cheap motor they run very smoothly at low speed. The only problem is that they are designed for high revs so you need to gear them down at least 3:1 to work well. My Z axis is about 2:1 if I remember correctly and the motor can get a bit hot if you keep running the Z up and down at rapid speed for a while. In actual use none of the motors get particularly hot. To get a suitable ratio you need to use different belts. I used 15mm HTD belts on X and Y. You can't easily change the Z axis pulley which is why I couldn't get the ratio I wanted. Be warned belts and pulleys can be expensive! If you are using the machine for work it is probably not worth spending the effort and time to use these motors. You would be better off finding a more suitable motor even if it is more expensive. As I mentioned before you need somewhere around 30 lb-in (480oz-in) continuous rated torque if you want to re-use the existing pulleys. As long as you are reasonably careful about screening and use good quality cable on the encoders you are unlikely to lose steps. That is what I really like about my servo setup. I don't have to worry that a stepper may have lost steps somewhere along the line. I use Gecko G320s on the mill and Rutex R990H on my lathe. IMHO the R990s give very slightly better performance but they are more hassle to wire up. Don't sell your Bridgeport. No benchtop machine will compete with it once you have it working correctly. Les rocketscientistnate wrote: I would love to do that. Where is the best place to get the servos? What size do I need, to gear them down and go undersize, or to go 1:1. I assume I'll need gecko 320s? What are the possible hang ups in doing this? With the encoders is it pretty much guaranteed that if its running the servos are going to be in the right place? I'm a little anxious as I have customers starting to breath down my neck. Luckily, the local college lets me use their Fadal when I'm broken down. :) I had almost decided to try to sell the whole machine and get a smaller benchtop one, that I could be sure would work. I thought if I go to servos, its my luck that it still won't work and then I'll have the same useless machine, and still be out the money for servos. |
