Our team has decided to try and use chains to drive our drive wheels, since we’ve had problems inserting a gear ratio (axles for gears can’t be mounted without interfering with wheels).
Is using a 1:2 ratio (24 tooth sprocket to 12 tooth) set up for speed with high strength sprockets and chain too much for a torque motor (bot weights roughly 20 lbs, lets say)?
Is it wise to chain all the wheels on one side together? If so, why? I’ve had some teammates say it solves issues with backlash and motor burnout, but I can’t figure out why. Would chaining sides together result in added stress on the motors? Would it solve anything in terms of backlash, precision while driving, or motor burnout?
I’ve noticed chain popping on other bots in competition - is there a big risk of this happening, especially with a gear ratio for speed and the stress of a full bot & sudden turns?
Last year for Skyrise, we geared our wheels together, but that was so that if the robot does a wheelie, we have 2 motors turning 1 wheel, rather than 1 motor doing something and the other just spinning. This year, it’s far less necessary, without lifts, although our turbo drive on 3.25" wheels can do wheelies if we really try (our driver does that a lot, we should probably put slew rate control on to fix it). I don’t think it solves any issues with motor burnout or driving precision, and I don’t quite understand what you mean by backlash.
Anyway, I think a 2:1 gear ratio should be fine for a 20 pound robot, but it will be cutting it close. I would instead recommend doing 1:1 external with speed gearing internally instead, but it’s worth trying the 2:1 to see if it works. One nice thing about sprockets is the ease with which the gear ratio can be adjusted.
As far as chain popping, just make sure your chain is not too tight, but also is not too loose. If it’s too tight, it will pop, but if it’s too loose, the chain will slip, and your motor will stop doing anything (the sprocket will be spinning, but the chain will slide over the teeth rather than moving). If you get the tension right, you should be fine. We have a 4 motor turbo drive on 3.25" wheels and about a 15 pound robot, and have the wheels on the intake side chained 1:1 so we have the motors together under the flywheel, and we’ve never had any issues with the chain popping or slipping, even when our driver pops wheelies.
I have seen both, sides chained together and individual wheels. I would recommend just doing it for each wheel so if one wheel gets jammed you don’t stall your whole side. It’s not that big of a risk but just to be on the safe side.
How many motors are you using on the drive? I am just going to assume 4 for the sake of the example. One of our teams has around a 20lb (idk exact) and he runs a 1:2 speed with torque motors and gears each wheel individually. It works fine for him but he just has to be careful about pushing people and stalling out.
There was a thread a while back started by @Stanley Shi(2R) which actually has a calculation to see if it would be OK to use a specific drive ratio, I will see if I can find it.
Definitely not, we recently changed our torque reduction chain gearing for our 2 motor drive train to a 4 motor drive with 1:1 to wheels and it gave us tons of advantages. It feels more responsive, less maintenance, and a much higher torque when pushing another robot. plus chain is a pain to get back on the sprockets.
By backlash I mean the slipping of the wheel back and forth when not turned by a motor (you can shake the wheel a bit without turning anything in the motor), which we fear may throw off precision when we’re programming the bot to move to the other side of the field during the Programming Skills challenge.
I have it chained for a 1:1.5 speed ratio right now since our teacher said that he’s had a lot of problems with the high speed motors burning out extremely quickly (we’re using 4 inch wheels)
Right now we’ve never tested high speed motors because our teacher is so strongly against them, but we’re currently running a 18:24 sprocket ratio for speed. We want to upgrade to a 12:18 or 12:24 but we don’t have the sprockets we need (will be buying them ASAP).
Apparently last year, my teacher experienced the high speed motors overheating within two seconds of being placed on the mat with no gear ratio :l
High speed motors are exactly the same as torque motors, just with a different gear set. Using speed motors is almost the same as a 5:3 gear ratio with torque motors. If you’ve had bad experiences with them, either the motor or internal gears were bad, or the application demanded too much torque. Each internal gear set has its advantages and disadvantages.
Torque motors are slow but strong, turbo motors are fast but weak, and speed motors are a good middle ground.