[macdowswe]

websrvr makes a very good point about the ability of the copper foil on a PCB to support the peak currents. Take note of his concerns.
I have met problems here myself. It's not just the current carrying ability, its also about how you connect TO the copper. Abrupt transitions between heavy connectors and light foil can be problematic, as shown here (commercial unit):
Attachment 343960
I did wonder why the driver had stopped working!
But there were other faults on the PCB as well. Eventually I replaced the 3 units with 3 Gecko drivers.

Anyhow, there are design guides on the web for the current carrying capacity of copper tracks.

Cheers
Roger

Thanks for the heads up.
I have tried to make sure that there is as much copper as possible in the current path that is expected to carry the motor current. The copper track impedance going around the motor current loop is approximately 1 milli ohm. This is 5 times smaller than the impedance through the MOSFETs in the same current path, so hopefully the amount of copper should be fine.
I have designed the board so that you can add a single heatsink for all the MOSFETs. There is also a thermistor placed as close as possible to each of the MOSFET group (3 thermistors total). The control algorithms will also have thermal control, so hopefully it should be fine with the current design. Of course if it turns out that things get too hot, we can always beef up the tracks at the cost of a larger PCB, or thicker copper at the cost of price.

[websrvr]

This 6,000 r.p.m. encoder also looks promising and can be found for $25.00 or less.
See the data sheet for more info.

JoeyB

The last encoder is intended for use on a large inertia <3,500RPM keyed shaft motor where the shaft DIA is >30mm or for example belt driven from a lathe spindle.

Roger,

Will the encoders I posted work reliably within the r.p.m. limitations of a 5tpi ballscrew?

JoeyB

Thanks for the heads up.
I have tried to make sure that there is as much copper as possible in the current path that is expected to carry the motor current. The copper track impedance going around the motor current loop is approximately 1 milli ohm. This is 5 times smaller than the impedance through the MOSFETs in the same current path, so hopefully the amount of copper should be fine.
I have designed the board so that you can add a single heatsink for all the MOSFETs. There is also a thermistor placed as close as possible to each of the MOSFET group (3 thermistors total). The control algorithms will also have thermal control, so hopefully it should be fine with the current design. Of course if it turns out that things get too hot, we can always beef up the tracks at the cost of a larger PCB, or thicker copper at the cost of price.

3oz copper PCB isn't expensive and would impact your per unit cost by about $0.25 at most and still be less than $5.00/ea with FR4, 1.8mm, HASL, Blue/White board.

How a pad is situated on the trace along with transitions along it's path are also important and you have to pay attention for current loops and ground loops on voltage and ground traces.