Bump climbing issues
 

Hello all. Archer003 from 1982 here.
We have been working on the drive train recently, and we discovered a flaw in our design. When we attempted to climb over the bump, the bot couldn't make it over. We are currently working on attaching some new sprokets to try to gain more torque, but if it doesn't work we need to have our bases covered.

What I need, is some help trying to come up with ways to make our torque better, without using more CIM motors, since we are close to the max 5 as it is.

I included pictures of the front of our bot, the front wheels, and a profile of the current gear box. This is kind of a big portion of our robot, because it is too tall to go through the tunnel, so a quick response would be great. Thanks in advance.

~Archer003

Re: Bump climbing issues
 

You say that you want to change the sprockets to add more torque. Does the robot not climb over because the wheels stop spinning? or because the wheels start slipping? Keep in mind that if the wheels are slipping as you try to climb over, changing sprockets, adding CIMs, or whatever else you do to increase torque won't help.

Re: Bump climbing issues
 

Good way to ask a question (rep given). A complete description of the problem, and some decent photos of the situation.

Anyway: It looks like those sprockets on the wheels are kinda small. I can't see exactly how many teeth they have, but if you double the number of teeth, you double the torque (but cut the speed in half).

Try something like that.

Re: Bump climbing issues
 

The motors stop spinning. Our driver says that it stalls when it hits the bumps, but when we pick up the bot, the wheels spin fine. So we think it is torque, because electrical, and code is all functional.

Re: Bump climbing issues
 

Thanks for the clarification. Do you know what your sprocket ratio is from the Toughbox to the wheels? As Don said, the sprockets on the wheels look a bit small.

Re: Bump climbing issues
 

Alright, but are there any certain stores/companies you know that could get us the sprockets? We want to avoid buying over the internet, a lot of our parts came in later than they told us, and we need to fix this soon, or we'll be stuck in 1/3 areas for the whole competion.

Re: Bump climbing issues
 

I agree with Don, nice job on asking the question and I also agree with his suggestion to try a larger gear on the wheel.

I have a question, there is a transmission in the picture, can you tell me which one it is? I think we are all looking to see what the gear ratios to the wheel is.

Re: Bump climbing issues
 

I'm pretty sure it's the Toughbox. It has a 12.75:1 ratio. I'd still like to know the sprocket ratio though.

http://www.andymark.biz/am-0145.html

Re: Bump climbing issues
 

Another place you may be losing power is in the gearbox/motor setup. If your motors, or some gears are slightly misaligned, this could cause a lot of friction and hurt your power output. I would test the current going through your drive train motors when the wheels are free spinning and compare that the the cim motor cure. If the current is high, this would indicate some resistance in the drive train. We had this issue last year, and a little bit of tweaking made a big difference.

-Seth

Re: Bump climbing issues
 

We considered this, but as I mentioned, we picked up the bot to test the wheels without the bump, and they were functioning fine. I think the motors and gears itself are properly attched.

Re: Bump climbing issues
 

Another consideration would be to use fisher price motors along with the Cims. AndyMark sells a good gearbox that takes a fisher price motor and has the same output as a Cim motor (so you can mount it right into the tough box).

http://andymark.biz/am-0347.html

Although the fisher price motors are currently out of stock, you could order the gearbox by itself, or wait a few days for the fisher prices to come in (I called AM yesterday and they estimate having the FPs in by Friday).

Your concerns about shipping are valid, but my team has had good success with AM shipping, so I would say with fast shipping that would be a safe bet.

However, as other people have said, lowering your ratio is probably the best solution, unless there is some other issue associated with that.

Re: Bump climbing issues
 

McMaster-Carr ships very quickly, unless you happen to have a McMaster distributor in the area, in which case you can send someone to pick the items up.

AndyMark might have shipping delays due to inventory shortages (something about 1000 teams all wanting the same item at once, or something like that), but once they ship, they ship quickly.

Also note that COTS items don't count against your withholding allowance (40lb). If they arrive at your shop before you leave for competition, bring them with.

Re: Bump climbing issues
 

It looks like that is a 10"-12" diameter wheel. To help we would need to know 3 things:
1) the diameter of the wheel
2) the number of teeth on the sprocket on the transmission
3) the number of teeth on the axle sprocket

If you are using the same wheels for all 4, you will probably not be able to turn either.

Something you can do right away is to swap in the KOP wheels and see if it is better.

Re: Bump climbing issues
 

you say the CIMs stop spinning... if you have any extra CIMs try swapping them out... they might be fried

Re: Bump climbing issues
 

As mentioned, it was fine in mid-air, but on the ground wasn't working, so I dont think its fried.