help with 6wd chassie..

[Magic]

Hello guys!

I'm 17 years old, and robotics is a big interest of mine.

Recently, I built a 6 wheels drivetrain chassie with a 1/8" center wheels drop.

the chassie looks like this one (the only defferance is that i'm using 2 motors in each side with one gearbox, two motors that goes to the same gearbox):


my problem is that i'm not a programmer, so i can't drive it. i wish someone can provide me a good code, which is Appropriate for 2 joystick drive so i can try it (one joystick for the right wheels and the other for the lefts).
please provide me the best code that you can, because i know nothing about programming and i can't amend the code.

in addition, i'll be very thankful if some one can provide me with a geartooth sensors code for this drivetrain (2 geartooth sensors, one for each gear).

thank you alot!

[ComradeNikolai]

Magic,

If you're using the RC from this year, you can simply go to IFI's website and download the default code (http://www.ifirobotics.com/rc.shtml, scroll all the way down to the bottom, it's the link called "2007 RC Default Code" or something) and this provides the functionality you were asking for by default. You have to plug the PWM cables into PWM 1 and 2, and have joysticks in port 1 and 2 on the operator interface.

To download the code onto the RC, you use the same link as above to get IFI loader. You then stick a serial cable into the program port on the RC and a serial port on your cable, turn on the robot, and hold down the program button until a little orange light (I believe by "program state") turns on, then you just have IFI loader download the "FRC_Default.hex" file.

What other functionality are you looking to add? If you're looking to reduce the sensitivity or compensate for one side being mechanically stronger than the other, we'd need more details to help.

If you have any further questions or specific requests, you can always PM me.

[Joe G.]

Looks very nice. Just one thing, you might want to watch the chain wrap on the output sprocket. As a general rule, 120 degrees of wrap is a good idea, where it looks like you have roughly 70 degrees in the picture. An easy fix for this would be to add an idler sprocket to bend the chain down and increase wrap, which could even double as an adjustable chain tensioner.

If you wish to learn how to program, I suggest you look into easyC Pro. It has an icon based interface that does much of the work for you, while still allowing for huge amounts of flexability.

What exactly does the orange arm on top do? It looks very cool.

[Magic]

first of all, i want to thank you guys for you help!

secondly, this chassie is not mine. it just looks like my chassie with one single difference (two motors goes to each gearbox).

Just one thing, you might want to watch the chain wrap on the output sprocket. As a general rule, 120 degrees of wrap is a good idea, where it looks like you have roughly 70 degrees in the picture. An easy fix for this would be to add an idler sprocket to bend the chain down and increase wrap, which could even double as an adjustable chain tensioner.

you mean that i need to add a sprocket on the chain that goes from the gear to the front wheels? (and just for knowlege, what are the Positives of increasing wrap? how can it affect (or improve) my driving?)

[Joe G.]

Exactly. We had a similar setup this year, and had an additional sprocket directly under the gearbox, so the chain went through kind of an S-bend, kind of like the whachamacalit on the back of a bicycle.

More chainwrap is a good idea because it prevents chain slippage. It may seem dead tight while stationary, but chains can do amazing (bad) things under power, and it could theoretically get ripped right off the sprocket. Having more teeth in contact with the chain can help this. Therefore, especially with smallish sprockets like those on the gearboxes, 120 degrees of wrap is generally a good idea (less is sometimes ok on an idler though)

[Magic]

i have used the default code for 6wd chassie, but it's not going straight. It's not a Mechanical problem. after a check i discovered that CIM motors favor one diriction than the other and that's the reason my chassie isn't going straight.

My question is: how did your team overcome/solve this problem? by correcting it in programming, using a sensor (do encoders solve the problem completly?) or maybe in another way?

Thanks,
Magic

[Matt H.]

Using encoders and a PID loop to equalize output on both sides will solve your problem however that is also somewhat programming intensive. Also the very nature of two joystick drive will make it very hard to drive your robot in a straight line.

[Alan Anderson]

CIMs have a negligible bias. Have you made sure your Victors are calibrated?

We have encoders on the left and right side gearboxes. The difference between the encoder counts represents the amount the robot has turned. We keep track of the current direction and do PID control of heading to maintain straight travel when the driver is not calling for a turn.