Is anyone willing to share how they sped up their robots for Worlds? We were able to get more speed by using a triangular gear/chain/wheel drive setup but there were definitely robots which were moving much faster than ours. Is anyone willing to share advice on what worked for them on the 2014-15 challenge?
Our Q Team sped up the robot by changing the gear ratio on the drivetrain. The robot had a 24 tooth sprocket on the motor and 16 tooth on the wheels. Increasing speed decreases torque, and we needed to have enough torque to push back a row of blocks. So we tested 32, 48, and 60 tooth sprockets on the motor. Performance started dropping off after 48 teeth.
The other trade-off was control. With a larger sprocket on the motor the movement of the robot was very jerky. The turns were very quick and it was difficult to get a precise turn. The robot was able to get down the row of blocks very quickly, but the driver had trouble setting the stack because the robot would move too far one way or the other.
Robots that were designed to slide along the wall and use the base of the stack to line up the robot would be able to go faster without sacrificing control.
That was our experience, but I’d be interested in hearing what other teams did.
In this picture the sprockets that are attached to the wheels have 16 teeth, the larger sprocket at the top of the chain has 24 teeth and is attached to the motor.
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Aloha elfrazier,
I’ll be glad to help.
One of the largest factors of speed that cannot be overlooked is the WEIGHT of the robot. Keep it light to achieve speed.
The next factor is to balance SPEED with CONTROL. A highly manueverable robot is just as valuable as a FAST robot.
The next important fact is SPEED and POWER act inverse to each other. Both must always be dealt with.
DRIVE gear is the gear plugged into the motor with an axel. The DRIVEN gear is the the gear up against the DRIVE gear. Its motion is dependent upon the DRIVE gear. The DRIVEN gear is usually the gear on the same axel as the wheel.
Here are some examples:
POWER set up: DRIVE = 12 tooth gear, DRIVEN = 60 tooth gear. 5 turns of the DRIVE gear produces 1 turn of the DRIVEN gear. Its very slow but highly powerful. Good for lifting heavy arms.
SPEED set up: DRIVE = 60 tooth gear, DRIVEN = 12 tooth gear. 1 turn of the DRIVE gear produces 5 turns of the DRIVEN gear. High speed but unable to push elements or heavy weights.
Our Worlds Set Up
DRIVE gear 60 tooth, DRIVEN gear = 36 tooth, 5:3 gear ratio, 1 turn of the DRIVE gear produces 1.67 turns of the DRIVEN gear. Good balance of SPEED and POWER for this year’s robot.
One last note, speed really isn’t everything. Manueverability is just as valuable. SPEED must be matched with CONTROL.
I hope these pointers help.
Have an awesome season!!
Mahalo Nui Loa,
Bailey
Aloha elfrazier,
Feel free to email me if you need any assistance.
-Bailey
The team I work with (2014 MasterBuilders, elementary), after competing with a slightly improved ClawBot on local and state level, wanted a very fast robot for the Worlds. Their motivation was programming performance, as the clawbot (while still letting them reach 75 points in autonomous) barely made 2 roundtrips over the field in one minute.
They built a drivebase with 3:1 speedup chain-sprocket design and tried to offset the lost torque by running 4 motors.
Yes, that robot was faaaaast. In the time their alliance partner started moving, they were already braced agains the walls down the block lane. But those walls were super-important, as the robot was very hard to maneuver and they had to completly rely on the field physical features to score. Placing the middle blue stack was a 10-20s exercise in patience, going back and forth over the base hoping that electron spins would align favorably and the robot, upon slightly touching the joystick, would only move less than half the block width this time.
It backfired in the programming challenge too, as gyro turns were very hard to do consistently (overshoot heavily depended on the state and level of the battery), so they ended up adding special rolling bumpers and resorted to complicated dances on the field to avoid dependance on the gyro.
Now, even though I thought (and still think) this gear was a bad choice, the countless (*) hours they spent with the robot on the field (and, let’s be honest, a great deal of luck) actually paid off, the robot had a bright minute and delivered as planned in the programming challenge. But should they have chosen a more conservative gear, I think they’d save enough time by doing much simpler, sensor-driven moves to compensate for the reduced speed. And they’d have better chances in the teamwork challenge too.
*) In the last month before Worlds, the robot was getting over 20h a week attention, either after school (open to 9PM, thanks Tammie!) or on weekends.
Nenik - Please post a picture of the 4 motor drive! Your post made me smile; we had a similar experience with one of our younger teams. We tested different gear sizes on the motor, and timed how long it took the robot to get from one end of the field to the other with each gear ratio. They loved that giant gear, the robot was crazy fast, but they couldn’t control it or stack at all. Eventually they came to their senses and went back to a smaller gear. But it was fun and they learned something.
This is the best photo I have at hand.
The wheel-driving parts are 8-tooth sprockets, fully hidden in 2x beam. Upper shafts were for the 2 motors (high enough to fly over blocks).
The chain was very tight. So tight that it needed a lot of driving practice time to wear out enough to actually rotate freely…
Interesting. Those chains do look tight. Did you try leaving a little bit of slack?
The tight chains bring to light another important factor for speed - reducing friction. Often if a robot is moving slow, or is slow in one direction, it is because something is rubbing or there is friction somewhere. Normally tight chains are good, but I’ve noticed that in Vex IQ they cause a lot of drag. Maybe it has something to do with the square shaft turning in the round hole. 
It was only the rear drive that was tight.
Square shaft in a round hole is fine - less surface touching and it is legal to use oil (not that it really helps much in this case - what helped was the kids drivng the robot for hours and hours). Adding slack (single additional chain link) amplified the loss of precision. Their program, as the very first thing, did a sharp right turn from the starting position, then rode the wall. With the tight chain, this was reliable. With one more link, the robot just bounced off the wall and went wrong direction (before their unequal drive could compensate for that).
One funny thing about this drivebase setup: the (quite heavy) robot slip-spinned a lot. Whenever the driver engaged full throttle from standstill, it took a while to really start moving. Then it was a rocket.
Aloha nenik,
The suggestion of using oil on the VEX IQ parts to reduce friction is permissible for classroom applications only. It is illegal to use a lubricant in the VEX IQ challenge as it is not a part of the legal parts list as of now.
Here is an example of a potential problem that could be caused by the use of illegal lubricants. If a team uses oil on a robot which is intended to be used only in the classroom could mistakenly be taken to a competition and used. Once this is discovered by inspectors and referees a disqualification could be called.
Last year at 2014 Worlds a VEX team decided to modify their motors which were intended for robots in classroom applications only. Mistakenly they installed these modified motors onto their VRC robot at worlds. It created a huge controversy in the world of VEX when these illegally modified motors were discovered. The word got out very quickly to the VEX community. The team even publicly apologized on the VEX Forum to the VEX community. Needless to say there were many upset teams.
It might be better to just avoid using non VEX IQ parts all together especially if there are future plans of participating in official VEX IQ tournaments…
Here is a link to a previous discussion about lubricants.
http://www.vexiqforum.com/forum/vex-iq-challenge-discussion/viqc-new-game-2014-2015-game/official-viqc-highrise-q-a/8009-are-lubricants-allowed
We also used 4 motors to add torque to our 2:1 gear ratio. But I have a separate question–we’re just starting to use Modkit and I noticed the motor speed option of 100%. Are the motors set to 100% by default or can they be sped up using Modkit. Just wondering if I have to use gear ratios again to increase speed, or just use Modkit to rev up the engines.
Please check out **ipanavigator **post 3 on gear ratios. You cannot go over 100% of the speed. Motors are set for -100 to +100 % (values -127 to +127) and anything out of bounds is normalized back to this range. You can achieve your speed with proper gear ratio. Using modkit you provide appropriate power to the motors.
From above example, “DRIVE = 60 tooth gear, DRIVEN = 12 tooth gear. 1 turn of the DRIVE gear produces 5 turns of the DRIVEN gear.” If you provide 100% power, then you can see this movement at max speed of this setup.
Thank you Surgeon,
Yup. Gearing is what is needed to increase speed or torque. (Depending what your team is looking for) The number of motors used just provide the power for powering the gears.
For example, we ran a two motor drive base. Based on the weight of our robot and the number of motors, we could push the speed up to 1: 1.67. We tried 1:2 but then our bot started dragging. If we were to go 1:3 I am sure our robot would drag even more because the motors used just did not have enough power to push this speed. If we really wanted to move it at this speed we would need to add a couple more motors.
I teach my kids that no matter how many motors they run, the speed won’t increase. If they have a 1:1 gear ratio. More motors in this set up will only allow the robot to move at the max speed of 1:1.
In general, more motors provide the power to move the gearing.
The big goal, at least for us this year, is to build a light weight robot.
Mahalo,
Bailey