Battery advice--12+ volts, low budget

[Daravon]

I have a robotic camera platform, currently using a tiny 12v SLA and PWM on the motors. The problem is one of the motors hits max duty cycle before the rotation speed is satisfactory, while the other motor has tons of headroom. In this application, run time is only seconds at a time, but good current-driving capability at 1A or so is somewhat important--hence the SLA.

I want to increase my voltage so that I can increase the speed of the topped-out motor; I can always throttle back with PWM. I would just buy another 12v SLA and run 24v. However now I'm adding more weight and wiring than desirable just to get more volts. But what else is there? I could use 15+AAs--very expensive for rechargeables, not sure alkalines would have enough balls not to sag the voltage. I could run 5 LiPos...extremely expensive. I could run 7-8 CR123s...at $1 each, it might not be too bad, but where do I get a holder?

Is there a common application for ~24v battery packs that I don't know about? RC cars, maybe?

 

[65535]

http://www.batteryspace.com/nimhbatterypack12v2200mah10xaaforwalkingrobot.aspx

Not too bad.

 

[lctorana]

I'd be tempted to try a welded pack of 10 AA or Sub-C cells, depending upon available size.

You see, I think you're more likely facing a problem of volatege sag rather than isufficient starting voltage, and your SLA may be wilting under the load.

 

[Daravon]

Any ideas on where to get such a welded pack? I don't have a spot welder, and my budget is small.

These are the motors I have:

http://www.allelectronics.com/make-a-store/item/DCM-245/6-RPM-GEARHEAD-MOTOR/-/1.html

I have two of theses running, one a full blast and one barely running, on the 12v, 1.3Ah SLA battery. I have measured the terminal voltage of my one SLA battery while the thing is in operation and it was around 12.4v; however I don't know how much of that is getting through the TIP120 darlington during the PWM cycles. An option I'm considering is getting another SLA for 24 volts, but putting the batteries off the rotating platform and on the ground with a wire. However, that would be a massive PITA with wires wrapping around and all.

If the motor specs are to be believed, two motor should only be drawing 200ma or so. In that case, I guess a couple of rechargeable 9v in series would work by the numbers, but the rotation speed of the platform is open-loop and fairly critical, so I would like to have approximately zero battery impedance.