Yes, current setting is a bit more cumbersome than on pololu's. The current is set by a combination of current sense resistors and torque jumpers. The resistors I have been using are 1 ohm and 0.5 ohm. The 0.5 ohm resistors give you 1 amp of current and the 1 ohm resistors give you 0.5 amps of current. Each coil has two spots for resistors in parallel so the current from each resistor just adds to the total. So to increase current by 0.5 amp you solder in 1 ohm resistors into the 8 remaining spots, or to increase by 1 amp you solder in 0.5 ohm resistors.
The actual equation is just 0.5V / R where R is the total resistance (added in parallel) of the two current sense resistors on each coil.
So it should be pretty easy using just the two values to get 0.5, 1, 1.5 or 2 amps max current. From the max current you can set the torque jumpers to give 100%, 75%, 50% and 20% of that max current setting.
On that note, I hope everyone got the email, the 1 ohm resistors I sent out to some of the beta testers were actually 180 ohm resistors. (with 1% resistors it's very hard to tell the difference and Mouser sent me the wrong ones.) If you got the bad ones or just need a set that I didn't include, let me know and I'll send some out.
Any thoughts on what a kit ought to include? Perhaps add in some 1.5 ohm resistors for a 0.3 amp step in current?
I looked into POT's and couldn't find anything that would handle the current (up to 3 amps) and also had the right range of resistance (.20 to 2 ohms.) for anything like a reasonable price. It's much easier when there is a Vref pin as in pololu's rather than a current sense resistor.
For a set of lever switches to work you would likely need at least 4 resistors in parallel rather than the two on the board now. Perhaps 0.5, 0.5, 1, 1.5. To keep it within the 10cmx10cm requirement of the cheap board houses would likely require smt resistors for at least 2 of those (which is OK). But I haven't seen dip switches at a reasonable price. At $2 from Mouser that would add $8 to the wholesale kit price just for the dip switches.
The actual equation is just 0.5V / R where R is the total resistance (added in parallel) of the two current sense resistors on each coil.
So it should be pretty easy using just the two values to get 0.5, 1, 1.5 or 2 amps max current. From the max current you can set the torque jumpers to give 100%, 75%, 50% and 20% of that max current setting.
On that note, I hope everyone got the email, the 1 ohm resistors I sent out to some of the beta testers were actually 180 ohm resistors. (with 1% resistors it's very hard to tell the difference and Mouser sent me the wrong ones.) If you got the bad ones or just need a set that I didn't include, let me know and I'll send some out.
Any thoughts on what a kit ought to include? Perhaps add in some 1.5 ohm resistors for a 0.3 amp step in current?
I looked into POT's and couldn't find anything that would handle the current (up to 3 amps) and also had the right range of resistance (.20 to 2 ohms.) for anything like a reasonable price. It's much easier when there is a Vref pin as in pololu's rather than a current sense resistor.
For a set of lever switches to work you would likely need at least 4 resistors in parallel rather than the two on the board now. Perhaps 0.5, 0.5, 1, 1.5. To keep it within the 10cmx10cm requirement of the cheap board houses would likely require smt resistors for at least 2 of those (which is OK). But I haven't seen dip switches at a reasonable price. At $2 from Mouser that would add $8 to the wholesale kit price just for the dip switches.