Author Topic: new here... howdy. Also, multi-stage belt drives?  (Read 2659 times)

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Offline createthisTopic starter

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new here... howdy. Also, multi-stage belt drives?
« on: August 26, 2015, 11:47:14 AM »
Howdy,

I'm new here. I'm a software engineer by trade. I've dabbled in basic electronics theory. I've got a small woodworking shop because I'm interested in material properties (it just kinda grew out of the need to know more about wood). I've got a crappy 3d printer for prototyping, and a website I made because it seemed like something cool to do: http://www.createthis.com

I aspire to get more metalworking tools in the near future, like a cnc mill, or maybe just a regular mill. I currently have a big floor mounted drill press and a TIG welder, neither of which I'm particularly good with.

A couple of years ago, I was pretty interested in servos, and wanted a larger format "smart" servo, so I made this: http://www.diyservo.com

I learned I don't want backlash in my servo, and therefore I couldn't use planetary gears, so I abandoned the project.

I've since picked up an interest in quad copters, which led to brushless motors, which led to me picking up a boosted board ( if you don't know what that is: https://youtu.be/tyNJYbwBWnQ ), which led to me ordering a bunch of parts for a custom e-skateboard drivetrain to use as a large format actuator.

I just finished my torque calculation this morning. Apparently my actuator will make about 292 oz-in torque: http://www.rcgroups.com/forums/showthread.php?t=2486645

But I really want about 9600 oz-in. (50 ft-lbs), so I'm going to need a 1:32 reduction ratio. I really want to use a harmonic drive gearbox, but I can't find them for sale anywhere other than ebay, and I can't really find what I want on ebay, so I'm investigating alternatives. ( Finding someone willing to sell me various harmonic drive gearboxes might solve my whole problem, I don't know )

I'm currently toying with the idea of using belts for this, since they're zero backlash. So... getting to the point finally... anyone ever make a multi-stage belt drive? What are the advantages and disadvantages? Anyone have tips for construction? I can't find much information on line. Seems like nobody ever makes more than a single stage belt drive. Why is that?

Thanks,

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Jesse
CreateThis.com

Offline cyberjeff

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Re: new here... howdy. Also, multi-stage belt drives?
« Reply #1 on: August 26, 2015, 02:59:30 PM »
Howdy,

I'm new here. I'm a software engineer by trade. I've dabbled in basic electronics theory. I've got a small woodworking shop because I'm interested in material properties (it just kinda grew out of the need to know more about wood). I've got a crappy 3d printer for prototyping, and a website I made because it seemed like something cool to do: http://www.createthis.com

I aspire to get more metalworking tools in the near future, like a cnc mill, or maybe just a regular mill. I currently have a big floor mounted drill press and a TIG welder, neither of which I'm particularly good with.

A couple of years ago, I was pretty interested in servos, and wanted a larger format "smart" servo, so I made this: http://www.diyservo.com

I learned I don't want backlash in my servo, and therefore I couldn't use planetary gears, so I abandoned the project.

I've since picked up an interest in quad copters, which led to brushless motors, which led to me picking up a boosted board ( if you don't know what that is: https://youtu.be/tyNJYbwBWnQ ), which led to me ordering a bunch of parts for a custom e-skateboard drivetrain to use as a large format actuator.

I just finished my torque calculation this morning. Apparently my actuator will make about 292 oz-in torque: http://www.rcgroups.com/forums/showthread.php?t=2486645

But I really want about 9600 oz-in. (50 ft-lbs), so I'm going to need a 1:32 reduction ratio. I really want to use a harmonic drive gearbox, but I can't find them for sale anywhere other than ebay, and I can't really find what I want on ebay, so I'm investigating alternatives. ( Finding someone willing to sell me various harmonic drive gearboxes might solve my whole problem, I don't know )

I'm currently toying with the idea of using belts for this, since they're zero backlash. So... getting to the point finally... anyone ever make a multi-stage belt drive?


Haven't made them, but have used them.

Not so sure about the no backlash. You will need a tensioner (or the weight of the motor on a pivot) if it isn't a cogged belt and that has to have some give.

Your torque requirements are probably above what you can get here:

https://www.servocity.com/html/smooth_hub_pulleys.html#.Vd4ijflViko

And garden and automotive stuff is probably overkill:

http://www.northerntool.com/shop/tools/category_lawn-garden+lawn-mowers+belts-pulleys+4294903686

Belt drive is fairly efficient so I see no real problems with adding an idler to make your reduction in two steps.

As far as calculating torque requirements, remember that torque for DC motors is maximum at stall or zero RPM. So, unless you want to  run very very very slow you need more torque than just the load. You'll get the most power at half the rated torque and the most efficiency at somewhat less than that.

Jeff

Quote

 What are the advantages and disadvantages? Anyone have tips for construction? I can't find much information on line. Seems like nobody ever makes more than a single stage belt drive. Why is that?

Thanks,

--
Jesse
CreateThis.com
« Last Edit: August 26, 2015, 03:01:15 PM by cyberjeff »

Offline mklrobo

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Re: new here... howdy. Also, multi-stage belt drives?
« Reply #2 on: August 26, 2015, 03:09:30 PM »
 ;D Hello!
Your request;
 Has anyone ever make a multi-stage belt drive? What are the advantages and disadvantages? Anyone have tips for construction? I can't find much information on line. Seems like nobody ever makes more than a single stage belt drive. Why is that?
The only thing I can think of at this time, is a belt drive called an autodrive belt system.
This is basically 2 triangular cones side by side, one tip is near the wide end of the other cone, and
visa - versa. The belt is linking the two cones. The purpose is to provide a gear ratio from one cone to
the other; The width of the cone(s) ratio from one to the other. I do not know if that is what you are
looking for?. An academic problem example can be found in the REA's Problem Solver's book, Mechanics or Statics.    Good Luck!  ;D

Offline bdeuell

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Re: new here... howdy. Also, multi-stage belt drives?
« Reply #3 on: August 26, 2015, 04:38:41 PM »
I designed a multistage belt drive a little over a year ago. I used GT2 belts for their anti backlash properties. In hindsight it probably wasn't the best approach to the problem. My opinion is that by the time you add tensioners to the design it creates too many components to be ideal compared to other technologies. When you have multiple stages it is difficult to tension the belts by moving one of the shafts which means tensioning using an idler pulley.

Harmonic drives are an awesome mechanism; low backlash, high gear ratios, and low weight. they are available  however i think they are still covered by patent so the price is high and the sources limited. I used some steppers with harmonic drives before i think they ran about 1.5K each with encoder. also i think 1:32 is actually a bit low for harmonic drives.

if you really need low backlash I recommend looking into cycloidal drives. they are supposed to have low backlash and high reduction ratios. however i have not found a good source for them, i did run across an industrial supplier but i'm sure price is prohibitive there. however they may be a little easier to fabricate than a harmonic drive.

Also there are many low backlash planetary gearboxes used in industry. However precision is key to these gearboxes. for the lowest backlash I believe they actually measure components (using a CMM) find the best fitting ones and then assemble them. even after that they might not get it right in which case they put that one aside build a new one.

I don't see why you need low backlash for a skateboard but to be fair i dont ride one. if your system really only experiences load/torque in one direction this isn't really an issue. if you get rid of this requirement it opens up your drivetrain options considerably.

Offline createthisTopic starter

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Re: new here... howdy. Also, multi-stage belt drives?
« Reply #4 on: August 26, 2015, 05:24:08 PM »

Haven't made them, but have used them.

Not so sure about the no backlash. You will need a tensioner (or the weight of the motor on a pivot) if it isn't a cogged belt and that has to have some give.

[...]

Belt drive is fairly efficient so I see no real problems with adding an idler to make your reduction in two steps.

As far as calculating torque requirements, remember that torque for DC motors is maximum at stall or zero RPM. So, unless you want to  run very very very slow you need more torque than just the load. You'll get the most power at half the rated torque and the most efficiency at somewhat less than that.

Jeff

Good info, thanks. Yes, these are cogged belts. Here's the parts list so far, including links to the belt and pulley parts: https://docs.google.com/spreadsheets/d/1k9Cnwwm4x43ejwWfrssY_DFm7a6TMI1JPrzzTkUxPp4/edit?usp=sharing

Offline createthisTopic starter

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Re: new here... howdy. Also, multi-stage belt drives?
« Reply #5 on: August 26, 2015, 05:29:09 PM »
I designed a multistage belt drive a little over a year ago. I used GT2 belts for their anti backlash properties. In hindsight it probably wasn't the best approach to the problem. My opinion is that by the time you add tensioners to the design it creates too many components to be ideal compared to other technologies. When you have multiple stages it is difficult to tension the belts by moving one of the shafts which means tensioning using an idler pulley.

Fair enough.

Harmonic drives are an awesome mechanism; low backlash, high gear ratios, and low weight. they are available  however i think they are still covered by patent so the price is high and the sources limited. I used some steppers with harmonic drives before i think they ran about 1.5K each with encoder. also i think 1:32 is actually a bit low for harmonic drives.

Yup. Freakin patents, man. I see whole servos going on ebay for like $150, but it's all piecemeal. Ratios are weird, no idea how to control them, etc.

if you really need low backlash I recommend looking into cycloidal drives. they are supposed to have low backlash and high reduction ratios. however i have not found a good source for them, i did run across an industrial supplier but i'm sure price is prohibitive there. however they may be a little easier to fabricate than a harmonic drive.

Ugh. Ok. I'll take a look.

I don't see why you need low backlash for a skateboard but to be fair i dont ride one. if your system really only experiences load/torque in one direction this isn't really an issue. if you get rid of this requirement it opens up your drivetrain options considerably.

Hey man, I'm not on the robot forum because I'm building skateboards. The skateboard was just my inspiration. It's pretty impressive watching a skateboard propel a 200lb man up a 25% grade. I just saw that and thought, man, that would be an awesome actuator. All these skateboards come with a belt on each motor and a 1:2 reduction ratio. I just think I probably need more, unless my math is wrong.

Offline bdeuell

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Re: new here... howdy. Also, multi-stage belt drives?
« Reply #6 on: August 27, 2015, 12:16:14 PM »
I don't see why you need low backlash for a skateboard but to be fair i dont ride one. if your system really only experiences load/torque in one direction this isn't really an issue. if you get rid of this requirement it opens up your drivetrain options considerably.

Hey man, I'm not on the robot forum because I'm building skateboards. The skateboard was just my inspiration. It's pretty impressive watching a skateboard propel a 200lb man up a 25% grade. I just saw that and thought, man, that would be an awesome actuator. All these skateboards come with a belt on each motor and a 1:2 reduction ratio. I just think I probably need more, unless my math is wrong.

we get lots of variety in what people post on this form and the non robotic topics can be anything from electric bikes to animated sculptures.

I am interested to hear more about what you are actually working on, I apologize if it is in your original post but i read it a few times and i'm not quite sure. Drive mechanisms are very interesting subject and i still have a lot to learn. I toyed with a few ideas in the past to create low cost high performance drives for robotics but never went anywhere with them.



Offline createthisTopic starter

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Re: new here... howdy. Also, multi-stage belt drives?
« Reply #7 on: August 27, 2015, 12:31:57 PM »
I don't see why you need low backlash for a skateboard but to be fair i dont ride one. if your system really only experiences load/torque in one direction this isn't really an issue. if you get rid of this requirement it opens up your drivetrain options considerably.

Hey man, I'm not on the robot forum because I'm building skateboards. The skateboard was just my inspiration. It's pretty impressive watching a skateboard propel a 200lb man up a 25% grade. I just saw that and thought, man, that would be an awesome actuator. All these skateboards come with a belt on each motor and a 1:2 reduction ratio. I just think I probably need more, unless my math is wrong.

we get lots of variety in what people post on this form and the non robotic topics can be anything from electric bikes to animated sculptures.

I am interested to hear more about what you are actually working on, I apologize if it is in your original post but i read it a few times and i'm not quite sure. Drive mechanisms are very interesting subject and i still have a lot to learn. I toyed with a few ideas in the past to create low cost high performance drives for robotics but never went anywhere with them.

Just a large format digital robotics actuator. Ideally, something precise enough to be used in a robot arm (similar to universal robotics arms, not big industry car assembly line arms). Also, preferably with a good torque to weight ratio, so it can be used to build large walking robots.

I just don't see a lot of this stuff in the market right now, so I'm exploring the idea. I figure once I get the mechanical/electrical stuff worked out, I can wire it into a CAN bus or something and make a bunch of them and just play around with inverse kinematics and such.

I've never worked with real industrial robot arms and I'm a software guy, so programming them interests me. I've got a few projects around the house it would be interesting to automate (lampwork, mostly).

This is more of a research vector for me at the moment than an implementation thing. However, once I find something I like, it'll become an implementation thing quickly and I'll stop researching much at all. Just kind of how I operate.

Offline mklrobo

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Re: new here... howdy. Also, multi-stage belt drives?
« Reply #8 on: August 28, 2015, 05:15:45 AM »
 ;D Hello!
I would like to introduce a comment on your indication of a research vector in this arena.
I  have found some good mechanical books for idea generation, such as;
Ingenious mechanisims, for designers and inventors, volume 1 - 10.
Schaum's outline series, theory and problems of Machine Design.
I like to tip toe through  mechanisims, from time to time, as it is fun to examine inventions.
Good luck!   ;D

 


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