Quote:
|
Originally Posted by Cadetdan
Our robot is having a really hard time making simple turns. What is happening is that for about 30 seconds it will work fine, but then it starts making jerky turns. Basicly it starts and stops the turn even when the sticks are in the full turn position. Its almost like it has a mind of it own on turns, we dont have this trouble going forward though! Im really lost at this point any help would be great.
We are using the Cim's as motors and have a 27:1 reduction with 4WD.
Dan B
|
Dan,
You have a lot of experience outlined above, believe it. There are a several problems I see here that point back to one effect. After you have run the battery down a little, (30 sec) the RC can no longer stay up. The RC goes into a sleep mode when the main battery goes below about 8 volts. The backup battery keeps the program running but no PWM outputs are enabled. That is why the robot appears to have a mind of it's own. If you check that battery status on the OI as outlined above you will see that the battery intermittently falls well below 9 or 10 volts. (you may not see 8 appear in the window but it is likely happening.) The fact that your robot "lays rubber" on a concrete surface is a good indication that the final gearing is a little high. It seems that 8-10 feet/sec is a good speed for battery life and control. A good rule of thumb is that a battery should last 3-4 matches. This gives a good indication that the current demand is not so high to cause the RC to sleep or to trip breakers. BTW tripping breakers make them very hot, so don't touch them right after a match.
The cause for all of this is documented (over the years in many threads) and is fairly easy to understand. When a robot uses four high friction wheels (or more) drive without steering, the output of the motors can lock during turns. (Four stalled chalupa motors exceed the maximum current available from a fully charged battery.) At best, the side loads on the wheel bearings produce incredible loads on the drive motors putting them in near stall conditions. The tighter and faster the turn, the worse the problem. You can decrease the effect in software (when turning) but the easiest fix is to eliminate side friction on one set of wheels by modifying the wheel design or adding different wheels. Omni wheels work great for this but do require some added practice for stability.
As far as radio interference goes, if your modem appears to be compromised it also may be due to the battery being pulled down by the intense currents generated by the drive during the turn. Anything that affects the battery can affect the entire robot.