Nema 34 Motors - good deal?

[jallenmorris]

I found this on ebay. Seller has a rating of 4...so I guess this seller is new. Is this a good deal?

http://cgi.ebay.com/4-Axis-Nema-34-s...item3effbb22d7

I'm going to be building a Joe's 4x4 Hybrid. I think I'd like to buy Nema 23's since my aim is to get this built for under $2,000 (closer to $1,500 would be great). Is that possible? the 8020 doesn't seem too bad, and the kit is about $350.

by the way, which is better for the kit...rack & pinion or lead screw? Any links to other threads that discuss the 2 would be great. Thanks

[PEU]

these motors impedance is 15uH that means the motor maximum voltage is 123V DC (sqrt(15) x 32) and the power supply offered is only 24v, that means the motors will be underpowered by 100v... I would pass or find a driver that could provide that voltage, geckos are ruled out their max is around 70V.


good luck

[jallenmorris]

Please explain how you come up with your numbers. I've never heard of anyone putting more than 36V to a set of motors before.

Are you saying Phase Inductance is the same as Motor Impedance?

24V for these motors did seem kind of low, but i think 123V seems way high.

Originally Posted by PEU these motors impedance is 15uH that means the motor maximum voltage is 123V DC (sqrt(15) x 32) and the power supply offered is only 24v, that means the motors will be underpowered by 100v... I would pass or find a driver that could provide that voltage, geckos are ruled out their max is around 70V. good luck

[ger21]

Gecko has determined that the ideal voltage for maximum performance is 32 times the square root of the inductance. So, for maximum performance with these motors, you'd need to drive them at 123V.

Prior to Gecko releasing this formula, it was common to just run them at 20-25X the rated voltage. This would put you at 128V+.

[jallenmorris]

Holy Cow! So how much does a suitable power supply cost for these things?

Also, 15 mh is listed as Phase Inductance (as listed in the motor specs) is the same thing as Motor Impedance?

Originally Posted by ger21 Gecko has determined that the ideal voltage for maximum performance is 32 times the square root of the inductance. So, for maximum performance with these motors, you'd need to drive them at 123V. Prior to Gecko releasing this formula, it was common to just run them at 20-25X the rated voltage. This would put you at 128V+.

[PEU]

your problem is not finding a 125V power supply, its the driver that only accepts up to 36v, so even if you use a 36v supply your motors will be using 1/4 of their torque.

These are motionking motors, there are better options such as the 9802 (50v) or 9801 (65v) both can be driven by geckos or similar drivers.

and on top of all this, the seller only has 6 as ebay feedback... if I were you, I would consider this offer only with local pickup.

[jallenmorris]

PEU, thanks for the reply.

I think your post about being underpowered was a bit misleading. While it is true, it seems that the industry is not ready to power these motors to their full potential.

Is the 9802 and 9801 motors or drivers? Motors is what I think you are saying, but just making sure.

One of my previous questions was for the Joe's 4x4 Hybrid, would Nema 23's be sufficient? evidently there are more specs than just the name to a motor so perhaps saying "Nema 23" is not enough information.

Originally Posted by PEU your problem is not finding a 125V power supply, its the driver that only accepts up to 36v, so even if you use a 36v supply your motors will be using 1/4 of their torque. These are motionking motors, there are better options such as the 9802 (50v) or 9801 (65v) both can be driven by geckos or similar drivers. and on top of all this, the seller only has 6 as ebay feedback... if I were you, I would consider this offer only with local pickup.

[jallenmorris]

You don't know if you learn anything until you apply what you think you know ;-)

So, here is another auction I found. Different seller too.

http://cgi.ebay.com/Gecko-G540-w-Thr...item1c127d1612

These are Nema 23's with Gecko G540 driver (no power supply though)

The inductance is 6.4, so square root of this * 32 = ~80VDC. The G540 will handle up to 50VDC, so that's not too bad considering. The price doesn't seem to bad either $485. How much should I expect to pay for a power supply?

Also, is the torque of these motors sufficient to run on a Joe's 4x4 Hybrid? I think i recall seeing builds using Nema 23's with G540 drivers.

Thanks, and I'm really enjoying the discussion. Hope it helps someone else too.