Re: Bump climbing issues
 

I find it very hard to fry CIMs, without purposely doing so.
However, testing it in air (no load) is very different than with a load.
You should make sure it works perfectly fine.

On the other hand, if they were working fine prior to testing and you find its bad now, a design change may be in order.

Good luck.

Re: Bump climbing issues
 

McMaster will get them to you tomorrow if you order by 6 pm today. You can also buy #35 sprockets in lost of other places, like Grainger. Use Google and see what's near, call them and drive there for same day service.

I know you lifted the robot into the air and it *seemed* fine, but we're trying to explain some of the finer points of drivetrains to you.

Measure the motor current with the wheels in the air. It should be only a few Amps. Let us know if you don't know how, happy to explain. (What this tells you is IF the gearboxes really are tight or not. They often are, and need an hour or 2 running time, unloaded, to loosen up. You can lose 25% or more of your power here!!!)

Please, please, tell us the sprocket sizes top & bottom! And how big those wheels are! We are problem-solvers by nature, we just can't help it, but a problem with insufficient data is our version of Hades. Have pity on us, tell us...

Re: Bump climbing issues
 

We anticipated a problem like this and changed the sprockets initially. We went with 11 and 32 from McMaster Carr and received them in 2 days. We discovered that putting two 11 tooth gears side by side we had to turn down half of the hub of one sprocket for the chain to clear the hub. Also we had a problem with the alignment of the cim motors as mentioned earlier. We ran the robot elevated and tested each motor in forward and reverse using a power supply to measure the current. After making slight position adjustments to the motors, no motor draws more than 5 amps @12.5 volts.
Also if you adjust your chain tensioners tooooooo tight you will load the system down.

Re: Bump climbing issues
 

We may have gotten it working today, but we are going to test it tomorrow. We have an assembly, so we were more focused on getting the kinks worked out to drive in the gym, so we will test the adjusted sprockets tomorrow, and I'll get back to you. All of you, thank you so much for the help!

Re: Bump climbing issues
 

I have a few questions.

Do you know the coefficient of friction of your tires on carpet? Can you calculate that? If your coefficient of friction is around 1, you should have no problems on the bump from that end.

What gear ratio is going through the box?

What happens when you drive your robot against a wall? Like, put your robot against a wall, and try to drive forward. Do the wheels spin in place?

You probably are short on torque. Ideally, when you're not shifting, you want your drive to be traction limited. If you're traction limited, your wheels will slip if you drive against a wall. This will probably require 2 more CIMs (you could use the FPs, but why wouldn't you use 2 more CIMs if you have them?) and an appropriate Toughbox gear ratio. It'll require you to move one or two around from the rest of your robot (you can probably replace them with FPs depending on the application), but it'll let you get over the bump or push a robot without moving at an unacceptably slow pace otherwise.

Re: Bump climbing issues
 

http://www.grainger.com They have local stores
http://www.mcmaster.com they can deliver next day if you order by 5pm Mountain time

Re: Bump climbing issues
 

Regarding sprockets, my personal favorite supplier for *inexpensive* sprockets is the "Burden Sales Surplus Center" at https://www.surpluscenter.com. With sprocket prices about 25% that of McMaster or MSC, they really can't be beat for teams on a tight budget. The problem I have with getting items from them is that UPS Ground shipping takes quite a few days from their location in Nebraska to our location in New Hampshire. However, with you being in Kansas, standard UPS Ground shipping may only be one day to you!

They usually ship items the day after the order is received, and are great folks to talk to on the phone.