pic: Bearing block idea

[Sh1ine]

We use belts in our Drive Train and use exact center to center distances. That allows us to skip the tensioner all together. Although in the real world exact C to C is not recommended it is not a problem for FRC robots. We have been using this style of drive train for the last three seasons and we have never had a belt fail or slip. I highly recommend it to all teams.

If you are going to use belts, I would suggest using a 5mm HDT belt that is 15mm wide. We typically use 24 tooth pulleys, you might be able to go a bit smaller, but I cannot say that we have tried it. The WCP center to center calculator works excellent. http://www.wcproducts.net/how-to-belts/

Before you machine any parts, order your belts and pulleys. If they are out of stock you will be kicking yourself in the end, we know from experience.

[BrendanB]

This was the first year we dipped into the realm of a custom drivebase with chain spacing in mind! We calculated the center to center spacing needed between the wheels then sent the plates off to be machined. We had a fall back plan which was inspired by something 2168 did which was to take round delrin and drill and off-center hole in the middle and you turn the spacer to tension as needed.

We assembled both bases in January and in that time they have gone through a lot of testing and about 30 matches without any significant stretch in the chain. When we assembled we used brand new chains so they were tight and since have worn in as they should developing a tiny bit to slack but it is still tight.

Our plan is if they become an issue later on in the season we will just replace all of the chains with brand new stuff and dry run the base for a few minutes to help break them in quickly.

I would highly recommend you look into something like this as it can save a lot of time and hassle over designing bearing block tensioners. It works great for our team because we have limited access to milling machines (either CNC or manual) so a simple plate drive with c-c wheels was far easier for us and saves some tiny bit of weight. IIRC team 359 used to put sliding bearing blocks in their drivebases up until around 2010 when they calculated c-c and never needed to adjust the tension that year and have since gotten rid of them completely.

It has been nice not having to worry about the chains for once!