Build Thread- Couple of Questions

[Jesse B]

Alright, well I've got a bunch of little questions pertaining to electronics, so I figured I'd just make one thread rather than a bunch of little ones I’m new to all this, so if I make any mistakes or misassumptions then be sure to let me know!

1. I'm working on a budget here, so I've searched www.alltronics.com and come up with two motors that make likely candidates. They can be found Here and Here.

This gives me a few options; for the first motor (6-wire unipolar), from my understanding, I can wire this as Unipolar, Bipolar Series, or Bipolar Half-Coil. Bipolar Series creates an increase of inductance of 400%, but lowers required amperage and raises torque output. I know that the formula 32 * sqrt(Inductance) gives you the recommended voltage; so my first question is, using a lower voltage supply (most likely 24v or 36v), what negative effects would it have on the performance of the motor? Would I be better off just running it as Unipolar/Half-Coil, or will the negative effects be minimal?

As for the second motor (8-wire bipolar), I understand this can be wired to Bipolar Series, Parallel, or Half-Coil. According to what I've read, Half-Coil seemingly changes nothing (which seems odd, so correct me if I'm wrong), so that option is out of it. Series does as mentioned above; Parallel seems to be the most beneficial to me, as you get a torque increase with only more amperage required. So which would be the 'best wiring' for this motor?

2. I’m looking to go the DIY approach for the motor drivers. I know people generally recommend against this saying it’s not worth it in the long run, but I’m doing this as a learning experience so it’s worth it to me. As for drivers, it kind of depends on which motor I decide on. If I use the first motor and decide to go Unipolar, I was just thinking the Linistepper V2. It’s simple, inexpensive, and seems to have all the features I could need for what I’m doing. If I decide to go bipolar (with either motor), then I can’t seem to make up my mind. If I went with the Unipolar motor wired as Bipolar Half-Coil, then I could use a circuit based off something such as the A3977, considering its low amperage. However, if I went with the other motor, then things get a bit trickier. Wired as Bipolar Parallel, it requires 2.8A per phase. The A3977 can’t handle this much current as far as I know, so this is a bit of an issue. I looked around for a bit on www.PMinMO.com, and the Toshiba 6560AHQ seems to fit my budget. It can handle in excess of 3-Amps, is capable of Full, Half, Quarter and Eighth Stepping, and is relatively inexpensive. Is this a decent driver, or is there something else I could make that would be better suited?

3. For a breakout board, I assume I don’t need anything real fancy. Again on www.PMinMO.com, I was looking at the 4-Axis DIY Breakout Board. I assume this will work fine?

Well thanks for reading through all of that, and thanks in advance for helping me out! If I left out any information, just lemme know

[rgammage]

Hello Jesse

The first motor with 6 wires can only be connected Uni-polar, which can be a blessing as the driver is simpler to design but is overall less powerful.

The second motor you can wire as you will .... Bi-polar parallel is the most powerful but the driver is far more complex ... so toss a coin!

Regards

Richard

[stirling]

Jesse - you are correct with your three possible wiring configs for motor 1. Generally speaking with a 6 wire motor, either unipolar (with a unipolar driver of course) or single coil with a bipolar driver will give best performance - personally I'd choose bipolar but if you're making your own I appreciate unipolar is probably? simpler.

With your second motor you forgot to add that it too can be wired unipolar but bipolar parallel is generally the best performer.

Can't help you with the drivers as I fall into the camp of it's not worth building your own but that's just me.

breakout - they mainly bring easy connection and opto couplers to the party but some include relays. Personally I use solid state relays for spindle control and such and the drivers I use have optos already so I just go for the easy connection ones. i.e. they're just a parallel connector to a screw terminal block on a pcb.

[Renaissance]

I'm going to throw these out there for you Jesse. You'll have to decide on their value or accuracy and tweak the data for your motors or needs.

I use them for motor selection (winding considerations) and checks and balances for suitability of speeds and feeds (torque), timing considerations and power supply overhead/voltage selection. I have three motors in total in two spreadsheets. You can see the scenarios for unipolar vs. bipolar-series on one, and comparison to another straight bipolar motor. One spreadsheet is specifically a high current bipolar. Things get a little crazy past 3.0A for a DIY setup.

I may have borrowed some info here and there or a rudimentary spreadsheet from these forums, but I don't recall. If there are inaccuracies I hope others point them out and they don't beat me up. No warranty is implied since I only use them for comparison and general selection criteria. They're in Open Office format.

Invariably, even if a driver is simpler to implement for a unipolar, I end up with bipolars. They make more sense to me.

[Jesse B]

Thanks a lot everybody! That helped a lot

[Jesse B]

Alright, so I’ve pretty much narrowed it down enough to know that I’m going to go with a Bipolar Driver. I’m just having a couple issues when deciding which of these motors to go with still. My wiring options would be Bipolar Parallel (100 oz-in of torque) or Bipolar Half-Coil (with 130 oz-in of torque). I found this chart…



So according to that, Half-Coil doesn’t give great low speed torque (but that motor is still rated higher), but has higher torque at high RPMs. Bipolar Parallel has good low and high speed torque. 100 oz-in would suffice, but 130 might be good insurance. I’m just wondering if one is vastly superior to the other or what not.

Thanks

[Crevice Reamer]

Hi Jesse.

Generally, Parallel is the best way to go, but on a 6 wire motor, half coil is the closest approximation of that.

You are now getting into apples and oranges territory. In order to help you choose which way to go, we need to know what USE these motors will be put to.

WHAT will they be driving? Mill? Lathe? Router?

HOW will they be driving it? Screw? Belt? Rack & pinion?

CR.

[Jesse B]

It will be a desktop router, but I'm hoping to be able to cut harder materials such as aluminum if I need to. It will be driven via 1/2"-10 lead screws. Here's a quick rendering on my design I'm working on (which still needs some refining). The footprint is approximately 18" x 15".



Thanks for the help,


- Jesse

[Crevice Reamer]

Ok, looking at the chart:

If you had an eight wire motor, Wiring it bipolar would give the most torque--100 oz in your case. Wiring it Unipolar or half coil will give you about 2/3 of 100 oz.

For the 130 oz motor, that is already RATED 130 oz for unipolar, so half coil will still give that same 130 oz, and that motor will run just a bit faster before stalling. You would get MORE torque by wiring the unipolar bipolar series, but the motor would stall at much lower speeds than the same motor wired half coil.

With a router, you will want the fastest motor speeds available. Neither of these is very powerful, and your application will be borderline for that reason--250 oz would be much better motors--but it WILL move.

CR.

[Jesse B]

Originally Posted by Crevice Reamer Ok, looking at the chart: If you had an eight wire motor, Wiring it bipolar would give the most torque--100 oz in your case. Wiring it Unipolar or half coil will give you about 2/3 of 100 oz. For the 130 oz motor, that is already RATED 130 oz for unipolar, so half coil will still give that same 130 oz, and that motor will run just a bit faster before stalling. You would get MORE torque by wiring the unipolar bipolar series, but the motor would stall at much lower speeds than the same motor wired half coil. With a router, you will want the fastest motor speeds available. Neither of these is very powerful, and your application will be borderline for that reason--250 oz would be much better motors--but it WILL move. CR.

Alright, thank you very much, that clears everything up. I did some quick math, and I figure I need about 90 oz-in of torque minimum. That's obviously only an estimate, but those 130 oz-in motors *should* work fine for now. I don't have a bunch of money laying around, so they'll have to do for now. Once I get this up and running then I can hopefully start to slowly upgrade everything. I just want something usable for now.

Thanks again,

- Jesse

[Jesse B]

Also, is there any way to calculate a motor's inductance by looking at other specs? With those 130 oz-in motors, they are a custom winding, so it doesn't say their inductance on the spec sheet. The only specs given are:

1.3A per phase
Resistance: 4.0 ohm

Thanks

[Crevice Reamer]

Originally Posted by Jesse B Also, is there any way to calculate a motor's inductance by looking at other specs? With those 130 oz-in motors, they are a custom winding, so it doesn't say their inductance on the spec sheet. The only specs given are: 1.3A per phase Resistance: 4.0 ohm Thanks

I would estimate their inductancd at about 6 mH. That would mean a best Voltage of about 80V. 48V should work fine though.

CR.