Yes, we are having this problem… We are a rookie team that is having problems developing our drive train.
We are using the two drill motors for 4 wheel drive to create a 3:1 ration along with our custom-fabricated tensioners. We at first had 2 wheels bolted together with the sprocket in between and we were tripping breakers whenever we tried to turn on the carpet (We have no problems on smooth surfaces).
Today, we went down to 1 wheel at each position and made new spacers for the axels. It seemed to work a little better, but we are still tripping breakers in a way that is not acceptable (Every few seconds doing 360s).
Does anyone have any experience or ideas on how to resolve this problem?? We also made custom motor mounts…we made sure that they are not “pinching” the motors, but could this be causing this problem?? We are running out of reasons why this may be happening…
How big are the wheels you’re using? The drill motor in high geared down 3:1 is going to theoretically make the wheel spin at 330 rpm. A 6" diameter wheel spinning this fast should (theoretically) make the robot move at about 9 ft/s. You need to gear it down more. The problem is that you have it geared so high (and spinning so fast) that you’re not getting enough torque. You are stalling the drill motors, upping their current draw to around 114 amps (per motor). This is why you’re tripping the breakers so fast (they provide 200 amps for a number of seconds). Gear them down more and you should be alright.
Hmmm, ok…that makes sense, but it doesnt seem like we are moving that fast. We are using 8" wheels, with the 3:1 gear ratio. We also have gears that are already machined for a 4:1 ratio…
Last year we used the drill motors, with transmission, on our robot and NEVER blew a breaker.
We had a 24 tooth on the drill motor and a 60 tooth on the 8" wheelchair wheels.
We also had the ability to shift gears.
Last year we were able to pull a fully loaded stretcher up and over the teeter tooter with no problem.
One of our secrets was the design of the motor mount. We made them out of aluminum. They were very crude but they were a great heat sink so our motors never got hot. The drill motors were fully enclosed.
If the drill motors are blowing breakers, it’s either because you have too much of a side load on them or, more likely, because you have them geared too high.
The reason your robot is not moving very fast is because the motor is running near stall (due to the load you are giving it)and therefore at a very high average current draw. Since the 30 amp circuit breakers are “thermal” devices, they will trip with high average currents and then will continue to trip more often after the first time due to the high internal heating. A quick fix would be to slow down the drive in software but the gear ratio change is what you really want to do. Even with a good gear selection some motors will heat up. Take the Fisher Price for example, it has a really inefficient fan inside to circulate air. Block the holes with a mounting bracket and you are just complicating the problem. To add to all that, the fan is just “friction fit” on the shaft inside the motor and when the motor temp reaches the melting point of plastic, the fan stops.
Although there is no track record on the “Chalupa”
motor, I am going to guess it will have a serious heat issue. It is designed for intermittant duty in an all weather environment so there is no air movement through the motor. The best method on this motor is heatsink in the mounting design.
Please make sure (with accurate measuring on a regulation playing surface) that your motors are not running near stall speeds and adjust gearing if they are. This will insure long life on motors and NO tripped circuit breakers.
Good luck all,
Al
I’m the team leader for his team (Team 871). I just wanted to drop a note saying we took the advice posted and dropped into LOW GEAR, the robot moves slower but we are very happy with the results. It has no problem pushing an adult.
Does anyone know what the highest gear ratio that would work for the drill motors in 4 wheel drive? I am just curious becasue I wanted to do this but my team decided otherwise.
*Originally posted by kacz100 *
**Does anyone know what the highest gear ratio that would work for the drill motors in 4 wheel drive? I am just curious becasue I wanted to do this but my team decided otherwise. **
In '98, the last year we ran without gear change, we ran 4 wheel drive with about 1:5 ratio in high gear driving the 6 inch wheels. We had Skyway wheels on the rear and home made “easy side slip” wheels on the front. That gearing was about as high as would work reliably, but we were still using Tekin speed controls that would sometimes shut down temporarilly due to built in overcurrent protection.
If you are running 4WD with four Skyway wheels, and are near max weight, probably 1:6 in high or 1:2 in low would be as tall as you should go. If you are transferring a lot of goal weight to the robot, that might be pushing things.
This info pertains to using drill motors only. Also, other posters may have different opinions.
I forgot to mention, we had 4 wheel drive. One motor ran two 8" wheels with one chain between them. We were also at 129.9 pounds. we ran with a 2.5 to 1 ratio.
Hope this helps
ok here is what we have - we have 2 drill motors moving a 4 wheel system. we doubled the 8’’ wheels in the front so that the front of the robot has 2 wheels on each side and single 8’’ wheels on the back. we use our drills in trans 1 and have a 1:4 ratio , being 18 tooth from the drill to a 48 tooth on the wheels. We never have a problem turning on any surface and can pull over 30 lbs. maybe this can help some people out there.
For heat problems, try some Artic Siliver between the motors and mounting brackets. I don’t know if it will help in this instance, but it lowered my CPU temp 8-12%. Someone want to give it a try and see if it helps?
We are using the Chiaphua motor for drive with 4wd.
With ~14:1 reduction and 10" wheels we get about 15fps.
Acceleration is good. When spinning the drag is quite high on carpet so you have to take it easy. When pulling the goal, don’t accelerate fast and you will get to full speed. A custom circuit and special code will be used to protect the breakers.
