I was toying with possible gearbox/transmission ideas as a start for next year, and I was wondering if polyurethane or however that is spelled rollers would work to transmitt power like a gear.
specifically, I was thinking about MrB’s white pages gear ratio thing that had an idea for a CVT at the bottom, and was wondering is high traction rollers would work.
overview: mrB had two cones side by side, one with the base at the top of the drawing, on with the base at the bottom, so there was a constant distance between them. And in between them was a gear/roller that could move in the space between them. At one end it was close to the base on one and the narrow part of the other, at the other end it was reversed . . so as you slide it back and forth the gear ratio changes. Gears could not work for this design, at least not without very very complicated tooth patters, and maybe not even then. But what if you used high traction rollers? It would even act as a clutch of sorts, if you could vary the tension.
so, how would I get good sticky stuff to put around cones? Also, the roller in the middle may be hard to move, so maybe an omni wheel type thing would be best. or just really powerful actuator to move it.
Frank,
Detroit has been experimenting with continuously variable drive systems for many years. They have been particularly suited for hybrid or all electrical vehicles. I know there is a great amount of info out there beginning with Popular Mechanics going back many years. I am surprised to not have seen any popping up in our robot designs but I do keep watching for them. There are a number of teams that have taken the shifting idea to a logical integration in robot design. Of particular note is Thunder Chicken’s multi-speed transmission of last year. I believe that there is a white paper on their design. It was not only impressively designed and implemented but was surprisingly small and very well engineered.
Our team has actualy built a CVT and it worked really well, but because of this years game we could not use it and fit everything else in to get under the bar.
190 had a toroidal CVT last year, and will have one again this year if we can get it in under weight. The hard part about the CVT is programming it, as it is a very complex system to model.
There are many other kinds of CVTs out there, from the cone/belt design (like in the Honda Civic HX), to variable geometry designs, universal joint driven (Varibox), etc.
i don’t think anyone is still following this, but i am really looking for somebody who has knowledge of a robot clutch system that can shift on the fly?? i was informed earlier today that there were several teams that could, and me and a friend are wanting to make our own… are there any quick and easy (or long and ardruous) processes we might need to work through that you could help us solve??
*Originally posted by mjt902 *
**i don’t think anyone is still following this, but i am really looking for somebody who has knowledge of a robot clutch system that can shift on the fly?? i was informed earlier today that there were several teams that could, and me and a friend are wanting to make our own… are there any quick and easy (or long and ardruous) processes we might need to work through that you could help us solve?? **
We don’t use a clutch, but we do shift on the fly by using two sets of wheels, one large and the other small. You can see pictures at our web site. See below.
I was talking to some of the guys on Christian Holland Team 107 at Midwest and they said they were working on a CVT drive system. They hadn’t worked all the kinks out so they didn’t include on this robot but what I had described to me sounded pretty cool.
*Originally posted by DougHogg * We don’t use a clutch, but we do shift on the fly by using two sets of wheels, one large and the other small. You can see pictures at our web site.
When I first saw these wheels, I thought they were spinning their wheels when they weren’t even pushing! It took a little while to realize that those wheels weren’t even contacting the carpet, and that they could lower them when they wanted to go fast.
*Originally posted by gwross *
**When I first saw these wheels, I thought they were spinning their wheels when they weren’t even pushing! It took a little while to realize that those wheels weren’t even contacting the carpet, and that they could lower them when they wanted to go fast. **
I thought they were different material for traction on the carpet and ramp, but then they were used on both. Very interesting idea.
116 designed a 2-speed transmission that can shift on the fly, and be built with limited shop capability. It is clutch less, but not extensively tested in competition.
This is from 2002, so note that the drill motor is different from this year. It was updated for the new drill motor, but no white page as yet.
A CVT is very, very nice, but one draw back. Sure, you can have a huge “gear selection” but their 1 drawback is their ability to hold torque. I’ll assume for FIRST drill motors, FP motors, and others in our kit, it will be fine, but that is why you don’t see more CVTs out there today. Their belts will slip under that high torque demand situtation!
I have tought of cone-shaped gears or so. I’ll be working on that during the summer and see if i can get it to work w/o the weight and size that I am currently thinking of!!
*Originally posted by Matt Attallah *
**I have tought of cone-shaped gears or so. I’ll be working on that during the summer and see if i can get it to work w/o the weight and size that I am currently thinking of!! **
I don’t think it will work at all. Either the cone gears will have a constantly varying pitch or more teeth will majically appear the further you go toward the larger side of the cone. Niether of those ways would work. So, unless you’ve got some patented gear technology I don’t know about, you’re probably bettr off sticking to high friction rollers or something of the sort.
** I’m not sure if this will help but our team this year shifted on the fly by using a little pnumatic cylinder to shift back and forth. We also added a spring to help the cylinder shift back to high from low. I don’t know if this helps you at all since I’m not exactly what kind of drive train your going for.**
One easy way to make a two speed tranny is to use the freewheeling mechanism on the back wheel of a ten speed bike.
(Not the shifter)
when you pedal a ten speed, as long as the wheel is going slower than the pedals, the pedals stay engaged. If you go down a steep hill, and dont pedal faster, then the pedals are just spinning, and the back wheel is going faster, right?
so you could have two separate motors driving a link the same way, with different gear ratios
when you are going slow, both motors will be engaging the wheel, and the high torque motor will be doing most of the work - once the machine gets beyond the top speed of the high torque motor its sprocket will freewheel (like the pedals on your bike) and the high speed motor will take over.
Only drawback, you cant go backwards, unless you add a reverse gear.
*Originally posted by KenWittlief *
**when you pedal a ten speed, as long as the wheel is going slower than the pedals, the pedals stay engaged. If you go down a steep hill, and dont pedal faster, then the pedals are just spinning, and the back wheel is going faster, right?
Only drawback, you cant go backwards, unless you add a reverse gear. **
If I’m not mistaken the majic behind that is called a one-way bearing. Interesting how you described it being applied to a robot. Instead of the one-way bearing, what about something like manual locking hubs on an old 4x4 truck/suv?
I dont think its called a one way bearing, its more of a cog. Ive taken them apart to grease them. It looks like an inside gear, with the teeth square on one side, and sawtooth shaped on the other.
The tab that engages it is spring loaded - when you pedal forwards it catches, when you pedal backwards the tabs slides on the sawtooth shaped edges.
Now that I think of it, the high speed motor doenst need this, only the high torque motor. So you could have a two motor tranny and use the high speed motor to go backwards when you need to.
More accurately, this is a one way clutch. It is the same design as a ratchet wrench. The wrench is just able to change direction as well as apply power in one direction and slip in the other.
*Originally posted by KenWittlief *
**The tab that engages it is spring loaded - when you pedal forwards it catches, when you pedal backwards the tabs slides on the sawtooth shaped edges.
Now that I think of it, the high speed motor doenst need this, only the high torque motor. So you could have a two motor tranny and use the high speed motor to go backwards when you need to. **
As said above, this is a one-way clutch. However, there are a few problems with your design:
The high-speed motor would be constantly operating in near-stall condition when accelerating, wasting a lot of electricity.
No reverse direction, unless you use a shifting clutch design that reverses the rotation of the gears. You cant just have the one-way clutch on the low-speed motor, because when you rotate the clutch in reverse, the engaging mechanism will catch. Think about it.
