Penny,
Hi! The geckos are great! A little more detail on the supply voltage: Geckodrive quotes (I'm doing this from memory) 24 VDC to 80 VDC for the drive itself. I've read a few times that 70 VDC may be a better top end value. On the high end your are looking at the lesser of either 80(70) VDC or 20 x your motor's rated voltage. On the low end you need the greater of 24 VDC or 4 x your motor's rated voltage. Anything in between will work with the higher values giving better torque and high end speed.
Your power supply will consist of, at minimum, a transformer, rectifier, and filter capacitor. Working backwards the capacitors you be looking for are called electrolytic capacitors. There are a few things to bear in mind:
1. The higher the capacitance (usually expressed in microfarads) the more filtering/less ripple. You would be suprised at how little is actually needed-3,000-5,000 ufarads will work if that's all you can find.
2. These caps have a second rating-their working voltage-which MUST be greater than the supplies DC voltage output. Else POOF! Doesn't matter how much greater-just greater. A few volts is actually sufficient.
3. Electrolytic capacitors are polarized, or polarity senitive. They have a plus lead and a minus lead. If you hook them up backwards (minus lead to positive voltage, plus lead to ground) they can and will explode.
4. You can use multiple capacitors in parallel. The total capacitance is the sum of the ratings of the individual units. They should all have the same voltage rating and, again, this must be greater than the DC output of the supply. By parallel I mean all the positive leads connected together electrically and all of the negative ones connected together.
Your bridge rectifier is the diode pack that turns AC from the transformer to pulsating DC that feed the capacitors. The rectifier will be subject to all the current flowing out of the supply and to the DC level present at the output. As with the capacitors, you want a bridge whose ratings exceed thee values. The rectifiers are rated for maximum forward current and peak inverse (reverse) voltage (PIV). If you had an 80 volt DC supply capable of 20 amps, a bridge with a PIV rating of 100 V and a current rating of 25 amps would suffice. But a unit with a PIV rating of 600 V and 60 amps would work too.
Your supply output can be roughly estimated by 1.414 x the transformer's AC output voltage. Thus to get close to 70 VDC out, we would look for a transformer with an output of 70 VDC / 1.414 or 49.5 volts. Great, but you will never find one. Find the closest rated a bit higher and lower and see where you end up: a 45 VAC out unit would give you about 63 VDC (so vour capacitors would need a voltage rating of 70 VD or greater). A 55 VAC secondary on the transformer would yield 78 VDC. Higher than we planned on, but under the Gecko's 80 VC max-so a likely candidate as well. Just to drive home a point the capacitor(s) for this choice would need to be rated over 80 volts. In the real world one to two volts will be lost at the the bridge rectifier, so don't be suprised when your actual output is a bit off from your calculations. I'd probably go with the lower of the two voltages to avoid stressing the drive.
Read the attached .pdf off of the Geckodrive site-there is a section on power supply considerations. Please don't omit the fuses-it's cheaper to burn one of them out than a drive!
Have fun!
Evodyne