Cimple Boxes

[midway78224]

We are stalling while turning. We ran a fully charged battery that was showing 12.9v but when we turn it drop down to 9.1v. We are running 8 inch wheels and the drive is 12(gearbox) to 22 (wheel sprockets). any ideas.

[Madison]

Originally Posted by midway78224

We are stalling while turning. We ran a fully charged battery that was showing 12.9v but when we turn it drop down to 9.1v. We are running 8 inch wheels and the drive is 12(gearbox) to 22 (wheel sprockets). any ideas.

What kind of wheels are you using? Are all of them powered?

You're struggling to overcome the force of friction that's opposing your skid-style turning. To fix that, you'll need to:

A) Reduce the friction between some of your wheels and the carpet.
or
B) Shorten your wheelbase somehow
or
C) Gear your robot lower, trading speed for more torque to help overcome the friction.

At this stage, I'd recommend option A. You may have success with C as well, though. ~8.5:1 is a really fast gear ratio for 8" wheels. You might want something closer to 12:1.

[Mk.32]

Originally Posted by Madison

What kind of wheels are you using? Are all of them powered?

You're struggling to overcome the force of friction that's opposing your skid-style turning. To fix that, you'll need to:

A) Reduce the friction between some of your wheels and the carpet.
or
B) Shorten your wheelbase somehow
or
C) Gear your robot lower, trading speed for more torque to help overcome the friction.

At this stage, I'd recommend option A. You may have success with C as well, though. ~8.5:1 is a really fast gear ratio for 8" wheels. You might want something closer to 12:1.

We had the same issue last year, and using 8inch omins in the front solved this for the most part.

Is this the 6 wheel C-Base frame?

[midway78224]

We are running a six wheel drive with 8 inch first wheels. All wheels are powered. We have some tough boxes that we will switch out for the cimple boxes at our next meeting.

[Mk.32]

Is the center wheeled lowered at least a 1/8th of an inch?
And tough boxes will help, a lot.

[midway78224]

Yes, they are lowered by the hole with the kit chassis which i believe is an 1/8th of a inch

[nitneylion452]

Are all the wheels rubber or are there some plastic ones?

[slijin]

Originally Posted by midway78224

We are stalling while turning. We ran a fully charged battery that was showing 12.9v but when we turn it drop down to 9.1v. We are running 8 inch wheels and the drive is 12(gearbox) to 22 (wheel sprockets). any ideas.

This is also indicative of a battery problem. Measure the battery voltage under a load and see what it reads.

[midway78224]

We are running 8 inch first wheels so they are rubber.

We test are 4 of our batterys around the same voltage the highest being a 13.2 and the lowest being a 12.8 and had all the same effect.

[cmwilson13]

Originally Posted by slijin

This is also indicative of a battery problem. Measure the battery voltage under a load and see what it reads.

not necessarily the internal Resistance of the battery is pretty high in 2009 our bot operated at 8.5 volts dropping to 7.5 when we started shooting on a fully charged battery
if you have a high enough load and enough motors going the voltage can and will drop below 7 volts on a good battery.

[slijin]

Originally Posted by midway78224

We test are 4 of our batterys around the same voltage the highest being a 13.2 and the lowest being a 12.8 and had all the same effect.

Originally Posted by slijin

Measure the battery voltage under a load and see what it reads.

emphasis mine; if by "test" you mean apply a multimeter across the leads, that just gives you a nominal voltage; internal defects stemming from extended operation or other reasons could prevent the battery from effectively providing a 12v power supply, which is why I suggested testing under a load. That being said, if you are having this issue no battery which battery you use, then it's unlikely that the problem lies with the battery.

[midway78224]

we ran all out motors at same time and it drop to 10v it only drop to 9v when we turned and it would stall out.

[Shaun Coon]

we had this problem too! you have to charge it longer even if it says fully charged because volt meters dont measure under load the battery wasnt fully charged. so charge them longer.

[DavidGitz]

Originally Posted by Shaun Coon

we had this problem too! you have to charge it longer even if it says fully charged because volt meters dont measure under load the battery wasnt fully charged. so charge them longer.

I highly doubt this would ever fix a problem, since I'm sure most teams (if not every single one) uses smart chargers that after reaching the battery's full charge state will drop the current output to a very small value for "trickle charging". What you are referring to is a concept called "surface charge", which Al talks about here:

http://www.chiefdelphi.com/forums/sh...47&postcount=8

Madison is most assuredly correct. Even if you find that one battery is indeed bad you should use the fantastic spreadsheet that JesseK made to help on this:
http://www.chiefdelphi.com/media/papers/2469

Since you are running 6WD, in the spreadsheet linked above consider it as a 4WD with a shortened wheel base. Make sure to find the appropriate coefficients of friction for your wheels. You did not indicate the type of wheels, just the diameter. Assuming you are using all KOP wheels the friction coefficient is about 1.

When I put in this data in this spreadsheet it shows that you are geared way too high (15 fps, wow...). It is important to go through a good design process when you are involved in this kind of competition. After putting in for the Toughbox that brings you down to 7.2 feet/second, much more tolerable and even able to rotate, how about that.

[nitneylion452]

Originally Posted by midway78224

We are running 8 inch first wheels so they are rubber.

We test are 4 of our batterys around the same voltage the highest being a 13.2 and the lowest being a 12.8 and had all the same effect.

Sorry, I hadn't noted the team number. In 2010, the KOP came with some plastic wheels in addition to the rubber ones. Try swapping your front and back 2 (or your middle 2 if you'd like) with some plastic wheels. The decrease in friction while turning will make the robot turn much more smoothly and might solve your stalling issue.

AM sells the plastic wheels for $12.00 each.

http://www.andymark.com/product-p/am-0494.htm