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Author Topic: Should track systems be driven from a rear wheel?  (Read 799 times)

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Offline SylvestreTopic starter

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Should track systems be driven from a rear wheel?
« on: September 17, 2013, 09:03:44 AM »
Hello,

I am building a rescue robot that must be able to carry a capacity of +175 pounds. So my question is, would it better to have the front wheel the drive wheel or the rear wheel the drive wheel?  Here is a very rough sketch of what my track configuration looks like.

Offline waltr

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Re: Should track systems be driven from a rear wheel?
« Reply #1 on: September 17, 2013, 09:26:05 AM »
No idea really on what work best but,
What I envisioned when looking at your diagram is:
If the Front wheel drive and is moving forward, then the tension on the tread must come along the top of the tread, around the rear wheel to the ground. So for going forward it seems the the rear wheel might be better where the tension on the tread is from the front wheel directly to the ground. However, this completely reverses when moving backwards and then there is the cases of turning.
Therefore, my finial conclusion is that it does not matter which wheel is the drive.

Offline SylvestreTopic starter

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Re: Should track systems be driven from a rear wheel?
« Reply #2 on: September 17, 2013, 12:36:09 PM »
Ok I think I understand you correctly.  Thanks for your input.  Are you saying that if its rear wheel driven, there will be more torque when going forward?

Just a note too, I am using chain and sprocket system for my tracks system.

Others, feel free to give your input too.

Offline bdeuell

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Re: Should track systems be driven from a rear wheel?
« Reply #3 on: September 17, 2013, 03:09:28 PM »
I would think a rear wheel drive would be better, here is my reasoning:

In a front wheel drive track the slack will be in the front section of the track, between the front driving wheel and the front-most wheel contacting the ground. Whereas a rear wheel drive track the slack will be in the top and front sections of the track, between the rear driving wheel and the front-most wheel contacting the ground. Note that the rear wheel drive design the slack will be spread over a larger length making it less pronounced. Additionally in the rear wheel drive design, the slack will tend to concentrate to the top section because it is a long unsupported section its weight will pull down causing it to sag and put tension on the adjacent sections of track. Both of these factors will reduce the slack in the front section of track where it engages on the front-most wheel contacting the ground and should provide smoother engagement of this wheel and the track. This is beneficial because there are forces from the ground acting on the track at this point and reduced slack means reduced chance of de-tracking due to these ground forces.

As previously mentioned the track will in some cases run in reverse (turning and backing up) where the rear wheel drive will be acting as a front wheel drive, but assuming you will be driving forward most of the time it would be best to optimize for that case.

P.S.
I recently finished up working on construction of a rescue robot with my college robotics club. I would be interested to see what you have developed for a robot design.

Offline SylvestreTopic starter

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Re: Should track systems be driven from a rear wheel?
« Reply #4 on: September 17, 2013, 08:26:21 PM »
Thanks bdeull for the detailed response. I have already designed my robot in CAD with a front wheel drive configuration,  but I am second guessing myself now that I remembered the results of my first iteration, which is why I asked.

I implemented a tensioner into my track design, which should take up the tension and also like I mentioned before, it is a chain and sprocket type of tracks system.

In my first iteration, I used a two sided belt with pulleys as my tracks.  The cogs were not deep at all and there was no tensioner, which could have been part of why it failed.

So with a tensioner, and chain & sprocket system, should a FWD configuration be alright?  I just don't want to have to redesign the whole robot, but if its necessary, I will.

I'd be happy to share my design, go to my website http://engineeering.weebly.com and click on 'VoltX Iteration 2"

FYI, The page is under construction still

Offline waltr

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Re: Should track systems be driven from a rear wheel?
« Reply #5 on: September 18, 2013, 10:23:45 AM »
Once you have the drive base built test which direction works best. At what your diagram shows either end can be the front or back. Once you test and decide build the stuff on top that dictates which is the front.

Offline SylvestreTopic starter

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Re: Should track systems be driven from a rear wheel?
« Reply #6 on: September 18, 2013, 12:55:09 PM »
If you take a look at my website  http://engineeering.weebly.com on the 'VoltX Iteration 2' tab, you'll notice that the drivetrain is actually integrated into the front so I wouldn't be able to do that.

Offline bdeuell

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Re: Should track systems be driven from a rear wheel?
« Reply #7 on: September 18, 2013, 02:13:59 PM »
Sylvestre, it looks like you have spent alot of time on your design, impressive work!

A front wheel drive is not necessarily a bad design, it would likely reduce chatter in the top section of the track compared to a rear wheel drive. My thoughts on how the system will function in each configuration are biased purely on reasoning, I have not yet had the pleasure of constructing a link/chain based track system and there is no replacement for constructing an actual prototype. Perhaps you could use your first iteration design as a test platform and outfit it with the new track design, that way you can identify problems and adapt the design as needed.

I think the tensioner will be a huge help in preventing de-tracking. Is the tensioner designed with a spring such that it can provide a more constant tension over a large deflection i.e. can it take up any slack or is it fairly rigid?

P.S.
If you want to check out the design I worked on for a rescue robot I posted it under the videos section http://www.societyofrobots.com/robotforum/index.php?topic=17245.0

Offline SylvestreTopic starter

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Re: Should track systems be driven from a rear wheel?
« Reply #8 on: September 18, 2013, 05:00:23 PM »
Quote
A front wheel drive is not necessarily a bad design, it would likely reduce chatter in the top section of the track compared to a rear wheel drive. My thoughts on how the system will function in each configuration are biased purely on reasoning, I have not yet had the pleasure of constructing a link/chain based track system and there is no replacement for constructing an actual prototype. Perhaps you could use your first iteration design as a test platform and outfit it with the new track design, that way you can identify problems and adapt the design as needed.


That's a great idea.

Quote
I think the tensioner will be a huge help in preventing de-tracking. Is the tensioner designed with a spring such that it can provide a more constant tension over a large deflection i.e. can it take up any slack or is it fairly rigid?


Yes your exactly right, the tensioner will be mounted with an extension spring attached to the arms that extend to those wheels.  It was just difficult to model in CAD/ mate in the assembly so I just decided to leave it out.

Quote
P.S.
If you want to check out the design I worked on for a rescue robot I posted it under the videos section http://www.societyofrobots.com/robotforum/index.php?topic=17245.0


I will definitely check this out

 


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