Well, i didn’t really know where to ask this, it is for a tracked bot tho, so anyway. I’m wanting to get the GHM-15 which is a 12v motor… however i was only planning using a 6v battery for logic/motors. How well do you think this motor would work with only 1/2 the rated voltage?
Probably would work very poorly.
i’d expect it to work half as good 
JK, but to be serious: under-volting motors isn’t bad at all. It will deffinately give a longer life to the motors and they should run at half their RPM and torque. Don’t quote me on that. I haven’t undervolted my motors for two years after I got a bigger battery. Was fine for me in experience anyways, so you should be alright.
hope that bit helps.
it will just run slower with less torque, probably around 40-45% of the rated amount for half the voltage.
I’d think the power output might be only 25% at 6v than at 12v. Assuming the resistance of the motor is constant, the below calculator shows a significant change.
I’m curious what resistance value did you use, i didnt see it on the spec sheet? You know its funny the majority of the motors they sell here are 12v but they don’t supply any batteries for them.
Edt: Hmm… im just curious how long 2 6v pack (series) would last?
that would be 12v @ 2800mAh, that motor at max output draws 2.33A the fomula should be simple. Would it be 2.8A/h * 2.33A = 6.5Hrs
lynxmotion.com/Product.aspx? … egoryID=48
No? 
Listed Information:
The Lynxmotion 12.0vdc Ni-MH 1600mAh battery pack is made from ten high capacity AA cells and 16 gauge multi-conductor wire for the best power transfer possible. The quick connect plug or wiring harnesses makes it easy to retrofit these battery packs into your cool robot design. This pack weighs 8.9oz., about half the weight of an equivalent Ni-Cad pack, perfect for your walking or fighting robot.
Note: These battery packs were rigorously tested with automated equipment that repeat the charge and discharge cycles, logging the capacity in mAh’s. **These battery packs routinely tested better than Sanyo packs, which cost three times as much. **-------> This dosn’t surprise me, LM is the best quality and the best prices!
huh! must have overlooked that one Well its only 1600mAh, which will last 3.7hrs @ 2.33A ?
1600mAh/2330mA=.7h is probably more accurate.
mAh is miliampere-hours which is the product of miliamperes and hours. this means a 1600mAh pack operating at 2300mA will last less than 0.7h (41 minutes.) I say less than because the harder you pull a battery the less time it has to chemically react inside and you get less time before it “appears” to be fully discharged. usually a battery running somewhere between a C/5 and C/10 discharge rate will actually get close to an hour, anything above that and you’ll get less. now the nice thing is that a brand new battery typically has as much as 40% more capacity than it’s label because the label is giving an average capacity over the life of the battery. somewhere around 250 full charge/discharge cycles and you are at parity with the label with typical nimh batteries.
heh, if you consider he is pulling at about 1.5C I would guess more like 30 minutes.
I think you will be disappointed with the motor at 6V. I don’t have the formulas handy but your torque and rpm will be less than 50% rated.
Just grab a sealed lead acid battery.
They have tons of oomph, last a long time and are reasonably easy to charge. 
In Australia I can get a ~5Ah one for $20-30 and a 12Ah one for ~$50.
At 2330ma draw a 12Ah one would last for just over 5 hours.
I bought a Tri-Track kit thinking I would power it with the 6V batteries I had on hand. It moved at full throttle, but was far from impressive. So I bought the 12V batteries mentioned above. Now it scoots.
Get the 12V batteries.
hmm… well i would like it to last longer than 30min before recharging. It would be $50 for 2 of them… thats a little more than im wanting to spend.
If you really want a long runtime, you should probably invest in some 4800mAH LiPo (Lithium Polymer) packs:
www3.towerhobbies.com/cgi-bin/wt … LXSGC8&P=7
Since they are LiPos, they are quite expensive. The advantage of LiPos over NiMH batteries are that they are generally lighter. Of course beyond the expense of batteries, you will also need to get a charger that can do LiPos.
I wouldn’t use them in a battle-bot or anything however, it isn’t as robust as NiMH if it’s not in a hard case.
Either way, it’ll cost you some $$$, but might be well worth it if it’s within your budget.
Alternatively, you can get 3000+mAH Sub-C cells relatively cheap these days. You can string a 10-cell pack and it’ll last quite a long time…
The cells I use are AA-size, 2500mAH NiMH made by Energizer. Duracell also makes similar cells and I believe I saw some 2650mAH cells yesterday when I was at Walmart. You can solder 10 of those together as well using “mini” battery bars. Since these comes in 8-packs, you can get five 8-packs and make yourself 4 packs… Just charge the others while one is running…