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Harness needed? — Parallax Forums

Harness needed?

FRC2370FRC2370 Posts: 128
edited 2012-11-13 07:00 in Robotics
I have a robot which I intend to ride, but while testing it (without sitting on it - not quite ready for that part yet) I noticed that it stops rather abruptly when the motors aren't given throttle anymore (like it just stops on a dime from that moment). And im wondering since im worried about me getting launched off of it at some point, would this 3-point race harness be a good investment? http://www.amazon.com/Corbeau-Black-3-Point-Bolt-In-Harness/dp/B0002GMUBE/ref=sr_1_8?s=automotive&ie=UTF8&qid=1352001727&sr=1-8&keywords=3+point+harness

The chair will sit behind the battery, which is up front
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Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2012-11-03 21:43
    You can certainly use a harness, but I'd suggest that you change the control electronics so it doesn't stop quite as abruptly except for an emergency stop. You're probably using DC motors with an H-bridge as the motor controller and these have a setting where they use dynamic braking, effectively shorting out the motor, rather than letting the motor coast briefly before braking or using intermittent braking to slow the robot down. You want the latter.
  • FRC2370FRC2370 Posts: 128
    edited 2012-11-03 21:50
    Yep. Using AndyMark CIM motors and Texas Instruments Jaguar motor controllers. They do have a brake/coast jumper on the unit, should i use that?

    And it will be used for representing my schools FRC team, and for applying to college, so should i put the harness in for precautions sake?
  • Duane DegnDuane Degn Posts: 10,588
    edited 2012-11-03 23:52
    FRC2370 wrote: »
    And im wondering since im worried about me getting launched off of it at some point, would this 3-point race harness be a good investment?

    How fast can the robot travel with a person sitting on it?

    $85 sure seems like a lot for a seat belt. I'd at least wait until you have the seat figured out before buying a seat belt. You might be able make one for a lot less using some nylon webbing or some seat belts from a junk yard. Some outdoor supply places sell material for making your own camping gear. They sell nylon straps and fasteners that could be used to make something like the 3-point harness you linked to. I doubt you'll need to worry about restraining someone at speeds normal automobiles travel so a homemade version may be good enough to keep the driver safe.
  • W9GFOW9GFO Posts: 4,010
    edited 2012-11-04 00:45
    On a slow moving, open vehicle like you have I would not feel comfortable using restraints. The ability to dismount the vehicle quickly in the event that it is heading into a dangerous situation is important. I would rather use a foot support or some other rigid structure to give the driver something to brace themselves with. Just having a seat that is slightly reclined might take care of the problem.

    If it was enclosed then the restraints make more sense.
  • FRC2370FRC2370 Posts: 128
    edited 2012-11-04 00:51
    With the current gearing, about 17 miles an hour. Enough for it to hurt since its driving mostly on tarmac. And the breaker switch is within reach so I could flip it if the robot starts going anywhere. I mean i think a harness, from safeties stand-point, would be a good idea. And trust me, for belts, especially for a 3-point harness, $85 is cheap. So considering its speed, and what its driving on. Harness? Yes? No?
  • W9GFOW9GFO Posts: 4,010
    edited 2012-11-04 01:29
    17mph is pretty fast. Certainly fast enough to get injured. Once you mount a seat it looks like the CG will be pretty high - and the wheel track is kind of narrow. If it tips over that would be a problem, with or without the harness. I wouldn't want to be strapped in when it tipped over - unless I was surrounded by structure.

    I have doubts that it can brake hard enough to throw someone out if they are sitting in a reclined seat with their feet supported. If it could then I would also worry about if flipping over forward.

    If you use a good seat that has side supports (not something like a plastic patio chair), mounted as low as possible and reclined, limit the speed so that it cannot tip over and provide a place to anchor your feet then I don't think there will be a need for a harness. If you are sitting straight upright like in a kitchen chair then sliding forward out of the chair will be easy. If you use something like a bucket seat that is reclined you will stay put much better and you have the added benefit of lowering the CG.
  • jdoleckijdolecki Posts: 726
    edited 2012-11-04 05:08
    Yes they are expensive because they are designed to save your life.

    Find a local car racer in your town chances they will have a set cheap

    The pro racers have to change them at a pre determined intervals regardless of their condition

    Also you can get a cheap fiberglass racing seat

    .
  • FRC2370FRC2370 Posts: 128
    edited 2012-11-04 07:24
    At the moment, im running a small chair where the seat is about an inch or 2 off of the chassis. How bad would a fiberglass race seat run me? Cause i think the harness would impress people from a safety stand point
  • Duane DegnDuane Degn Posts: 10,588
    edited 2012-11-04 11:10
    FRC2370 wrote: »
    With the current gearing, about 17 miles an hour. Enough for it to hurt since its driving mostly on tarmac. And the breaker switch is within reach so I could flip it if the robot starts going anywhere. I mean i think a harness, from safeties stand-point, would be a good idea. And trust me, for belts, especially for a 3-point harness, $85 is cheap. So considering its speed, and what its driving on. Harness? Yes? No?

    17 mph? Wow. With a person on it? Wow.

    Ignore what I said before (in case you already haven't).
  • FRC2370FRC2370 Posts: 128
    edited 2012-11-04 11:41
    So does anyone know where i can find a cheap, decent fiberglass race seat (a street model, not competition - theres a diference). I found one from Sparco: http://www.sparcousa.com/product/speed-2 but then I would also need a a $110 4-point harness. Suggestions on a slightly cheaper method? possibly with the Corbeau 3-point harness?
  • ercoerco Posts: 20,256
    edited 2012-11-04 14:24
    @FRC: Sounds like you already know the answers to your questions. Post a vid when you can, we all want to see you riding this 17 mph bot... safely.
  • FRC2370FRC2370 Posts: 128
    edited 2012-11-04 14:54
    So the best set up I can track down is a Corbeau Forza seat: http://www.amazon.com/Forza-Black-Cloth-Game-Chair/dp/B0002GMSEI/ref=sr_1_cc_1?s=aps&ie=UTF8&qid=1352069329&sr=1-1-catcorr&keywords=Corbeau+forza
    And a Corbeau 4-point harness: http://www.amazon.com/Corbeau-Black-4-Point-Bolt-In-Harness/dp/B002Y2ZUK2/ref=sr_1_cc_1?s=aps&ie=UTF8&qid=1352069465&sr=1-1-catcorr&keywords=Corbeau+4+point+harness

    This set-up seem good?
  • W9GFOW9GFO Posts: 4,010
    edited 2012-11-04 15:50
    FRC2370 wrote: »
    Cause i think the harness would impress people from a safety stand point

    If your interest is safety, look for examples of how similar vehicles protect their drivers. Racing Karts are the most similar vehicle I can think of, they go much faster and do not use any restraints.

    If you really are going to be going 17mph on tarmac then there is the very real possibility of overturning. You do not want to be attached to an open vehicle in that situation. I think you'll find that multi point harnesses are only used in vehicles that have the driver surrounded by structure.

    If there will be no possibility of overturning or other crashes then I guess using a harness as a decoration would be okay.

    Another way to state this - a harness is not the thing that is going to make your 17mph vehicle safe. Better to wear a helmet, gloves and proper clothing.

    As for a seat - google "racing kart seat"
  • FRC2370FRC2370 Posts: 128
    edited 2012-11-04 15:55
    Well its wider than it looks (About 34 inch side to side, 30 inch wheel to wheel) and actually really low to the ground. If need be it can always be widened, and I'm planning on installing a roll bar of some sort. I'll put up pictures as I go. Kart race seats aren't really any cheaper than the Corbeau seat if your buying a quality seat
  • ercoerco Posts: 20,256
    edited 2012-11-04 16:07
    It is kart-like. A strong roll cage would impress, safety-wise.
  • FRC2370FRC2370 Posts: 128
    edited 2012-11-04 16:10
    I happen to race karts in the VT Shifter Series, so we designed it as kart-like as possible. So how would a roll cage be fabricated on something made out of inch-thick extruded aluminum
  • NWCCTVNWCCTV Posts: 3,629
    edited 2012-11-04 16:28
    FRC2370 wrote: »
    So how would a roll cage be fabricated on something made out of inch-thick extruded aluminum

    Very carefully!!!!! Aluminum round bar welded to the extrusion. Careful when welding aluminum. Once you get started go like hell because if you stop you will end up with a puddle of aluminum. You could also just bolt it on, but if you are out to impress then welding is the way to go.

    Edit: Here's a good seat that is probably a better fit. http://www.ebay.com/itm/Go-Kart-Seat-Padding-All-Surface-Full-Sets-New-/370557907017?pt=AU_Go_Kart_Parts_Accessories&hash=item5646f8f049
  • FRC2370FRC2370 Posts: 128
    edited 2012-11-04 16:34
    Well if I was to do the bolting approach, how thick and where would I find the metal?
  • FRC2370FRC2370 Posts: 128
    edited 2012-11-04 19:44
    Just got ahold of my frc team mentor (guy whos helping with this project). Im ordering a Sprint race kart seat, and a Sparco 5-point cam-lock harness. I'll post photos as we go
  • NWCCTVNWCCTV Posts: 3,629
    edited 2012-11-04 19:49
    FRC2370 wrote: »
    Well if I was to do the bolting approach, how thick and where would I find the metal?

    That all depends on the actual weight that needs to be supported along with a little extra for impact strength. I am by no means a math expert but I am sure someone here could figure it out if given the approximates.
  • FRC2370FRC2370 Posts: 128
    edited 2012-11-11 16:38
    heres the complete project. Got a JEGS Racing 70250 Polyethylene seat with a RACEQUIP 5-point latch-and-link harness. Rode it around and boy does it need the restraints. Never felt like it even came close to leaving the ground. Will post videos soon
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  • jdoleckijdolecki Posts: 726
    edited 2012-11-12 11:52
    That looks great.

    Also there is a science behind anchoring them to the chassis. Google " Anchoring a 5 point harness"

    And its reusable so it can always be moved to your next bot.

    And you are wearing a full face helmet I hate to see you do a face plant on that thing.

    As for your roll cage search for chassis shops in your area.

    http://www.vermontracing.com/cms/index.php?page=vendors
  • FRC2370FRC2370 Posts: 128
    edited 2012-11-13 07:00
    I've been wearing my motocross helmet while driving this thing. I'm in the midst of planning a new design for this robot thats a bit more efficient and can accept a roll cage. So which shop in that link should I contact? since none of them seem terribly close
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