{"id":1086,"date":"2010-01-15T07:44:23","date_gmt":"2010-01-15T12:44:23","guid":{"rendered":"http:\/\/www.plastibots.com\/?p=1086"},"modified":"2015-02-23T22:40:25","modified_gmt":"2015-02-24T03:40:25","slug":"dualgrip-nxt-rover","status":"publish","type":"post","link":"https:\/\/www.plastibots.com\/index.php\/2010\/01\/15\/dualgrip-nxt-rover\/","title":{"rendered":"DualGrip-NXT Rover"},"content":{"rendered":"

Sometimes I build robots that attempt to solve real world challenges.\u00a0\"\" Other times, robots are built based on random ideas. This robot is a case of solving a LEGO challenge – specifically, with their Technic tracks\/treads<\/a> #575518.\u00a0 At no fault of theirs, these plastic tracks are slippery on many surfaces.\u00a0 Great for carpets, flat areas, dirt (if you dare) – and great for turning as well.\u00a0 However, when you try to climb with them, they are as slick as ice.<\/p>\n

\"\"<\/a>
<\/p>\n

If you Google them, you will find some great ideas on making these treads more ‘sticky’.\u00a0 Some have used 1\/2 Technic pins (which fit nicely into the supplied holes), others have used elastics wrapped around them – all great ideas that work fine.\u00a0 I attacked the challenge from a different angle.\u00a0 The result is DG – or Dual Grip<\/strong> (yes, the name is somewhat plain).\u00a0 DG went through numerous revisions as I worked out kinks related to weight, stability, traction, sensors, flex etc.\u00a0 At the bottom I have included some pictures on previous versions of DG – some changes significant, others subtle.<\/p>\n


<\/p>\n


<\/p>\n

The idea was to have a treaded robot that could navigate varying terrain, turn quickly and of course, climb.\u00a0 Based on my experience with my other robots using the same tracks (eg UNV <\/a>and DynaTrax<\/a>), I found that they were not very good when it came to inclines.\u00a0 I figured that the LEGO rubber wheels have great traction on most surfaces, so why not slap a set of them along with the treads.\u00a0 However, this posed another challenge.\u00a0 I did not want both wheel systems in contact with the ground at all times as this would make turning tougher and be redundant.<\/p>\n

<\/p>\n

In normal running state, the entire drive system runs parallel to the ground.\u00a0 The wheels do not touch the ground at this point.\u00a0\u00a0\u00a0 When the robot meets an incline, the drive wheels are angled down which puts the rubber in contact with the ground.\u00a0 At this point the tracks have little to no contact with the surface.\u00a0 The following set of images shows the two drive states.<\/p>\n

\"Dual<\/a><\/p>\n

I considered creating a dual drive system with rubber wheels and tracks separated by a mechanism that would deploy the rubber wheels downwards when needed. However, after some thinking, I decided on an alternate route.\u00a0 In order to make it easy, light and effective, I figured the most effective way of doing this was to build the rubber wheel drive directly into the tread drive and have the entire structure rotate to change contact points.\u00a0 I am sure there are numerous ways this could be done, but this seemed like the easiest and most obvious approach.<\/p>\n

[ad name=”GoogleAS728x90″]<\/p>\n


<\/p>\n

How does it work?<\/strong><\/p>\n

The current version of DG functions in a dual state mode – a combination of both autonomous and remote control activity – all working at the same time.\u00a0 The autonomous portion consists of the NXT brick, a Mindsensors Accelleration Sensor (2 axis2\/g), and an NXT motor.\u00a0 The remote portion uses the Power Functions system with a remote control. Its purpose is to drive and steer.\u00a0 When running, the NXT is monitoring the robot via the Mindsensors<\/a> Accelleration Sensor and can detect when DG is beginning a climb.\u00a0 When it detects a certain (consistent) level of G’s, it triggers the NXT motor to deploy causing both sets of track\/wheel combos to angle themselves.\u00a0 This results in the wheels making contact with the ground, and the treads loosing contact (more grip).\u00a0 When the robot reaches level ground, it reverses and returns the tracks to level.<\/p>\n

\n<\/object>\n<\/p>\n


<\/p>\n

The following picture shows the deployment mechanism. .\"\"<\/a>The NXT motor, drives through a 90 degree angle gearbox<\/a>, through to a Technic worm drive, which then turns a 40T gear. The Technic gear is connected to two arms which are connected to each set of drive track units.\u00a0 When deploying, the track units are able to rotate. When I first began building this, I was not sure that the setup (click the image) would support the torsional stresses and weight of the robot. Turns out, it’s not an issue. The NXT motor, gearbox and 40T gear have no problem angling the tracks. From a code standpoint, the approach is straight forward:<\/p>\n

    \n
  1. Poll the Accel sensor every 100ms. Read result. <\/li>\n
  2. Make room for error and average the readings (the robot will shake and rattle which will throw off finer readings, so average the result – say every second).<\/li>\n
  3. If Accel value is above threshold, trigger deployment of wheels (robot is climbing).\u00a0 Note – I have this setup currently only to trigger when climbing forward. When going backwards up an incline it won’t trigger. This can easily be changed.\u00a0 Also note that depending on which way the sensor is mounted, the threshold value you are measuring could be + or – .\u00a0 In my case, it is .<\/li>\n
  4. I have attached a sample of the RobotC program below.<\/li>\n<\/ol>\n

    [ad name=”GoogleAS728x90″]<\/p>\n

    I had some of those cool 90 degree gearboxes on hand which worked well for DG.\u00a0\u00a0 \"\"<\/a>Part of the NXT motor, and both gearboxes (shown right) are ‘floating’.\u00a0 Namely, the two gearboxes are not connected to the main frame of DG.\u00a0\u00a0 The NXT has pins connecting it to the chassis at the back and the worm drive connects via the axle through it.\u00a0 Both gearboxes are supported only in that they are flush with DG chassis. The best part of this all is that it does not matter.\u00a0 Even with all the torque generated at these points, all the pressure is downward.\u00a0 Since their are already sitting flush with the chassis, it works just fine.\u00a0 You might argue that the torque then puts undue stress on the component holding the large gear, but I have not seen this and feel it is partly due to its structural design.\u00a0\u00a0 Consider that the deployment mechanism has forces being applied equally from both sides (each wheel drive unit) and then downwards.\u00a0 The wheel units cancel out the side forces and the downforces are canceled by the chassis supporting the deployment unit.\u00a0 Notice that the wormdrive gearbox shown is the old one (that skips). Click the image.<\/p>\n

    The following shows another angle of the wheel deployment mechanism.\u00a0 Also shown just below the NXT Brick is the Mindsensors Acceleration sensor. (click for large view):<\/p>\n

    \"\"<\/a><\/p>\n

    [ad name=”GoogleAS728x90″]<\/p>\n

    Problem:<\/strong><\/p>\n

    One problem that did arise was with the choice of gearbox.\u00a0\u00a0 The below image shows two LEGO geraboxes.\u00a0 At first, I used the newer Technic gearbox (left).\u00a0 However, after some testing, I found that the worm gear would begin to slip due the torque being put on it.\u00a0 So, I swapped in an older Technic gearbox, which worked like a charm.<\/p>\n

    \"\"<\/a><\/p>\n

    Next Problem:<\/strong><\/p>\n

    \"\" Admittedly, I tend to build my robots with little planning. \"\"<\/a>Usually it’s a few visual and technical thoughts in my mind and then I just fire up and build.\u00a0 This also leads me to have to rebuild bits one or more times.\u00a0 The small image shows a top view of the drive gear system. Take note of the 24T gear and the lack of axle coming out where the tread link comes close to the edge. In earlier iterations of DG, I had a 6L axle running through there and it stuck out a bit. This was also fine for earlier versions of DG as it was longer and the treads did not come close to the 6L axle. However, as DG progressed, the wheel\/drive system got shorter and more compact.\u00a0 What this resulted in was the tracks being very close to the L beam and 6L axle.\u00a0 The problem was, I needed the 6L axle running through there to connect the 24T gear – at the time there was a need to have it secured with a 1\/2 bush<\/a> as well.\u00a0 The 24T gear is driven by an 8T gear which is powered by the motor. So, there is a LOT of torque on this guy.\u00a0 When I fired up DG for the first time, there was a lot of racket as each track rubbed on the axle.\u00a0 Additionally, the torque caused the system to pull apart the 1\/2 bush on the axle. As I was digging around for a solution, I came up with the Technic 5.5 axle with stop<\/a>. Crisis averted!\u00a0\u00a0 One of the issues was that when driving, the torque exerted on that gear required a full axle as well as the L beams to give it strength.\u00a0 The 6x axle was too long and even though I could have just pulled it away from the treads, that would not provide the ability to keep the whole assembly from flexing and coming apart.\u00a0 The 5.5 axle with stop allowed me to put the axle between two beams which were secured together and not need 1\/2 bush on one end.\u00a0 Crisis averted.<\/p>\n

    Showing the deployment mechanism:<\/strong><\/p>\n


    <\/p>\n

    \n<\/object>\n<\/p>\n


    <\/p>\n


    <\/p>\n

    First run…<\/strong><\/p>\n


    <\/p>\n

    \n<\/object>\n<\/p>\n


    <\/p>\n


    <\/p>\n

    Another attempt:<\/strong><\/p>\n


    <\/p>\n

    \n<\/object>\n<\/p>\n

    <\/p>\n

    Close-up of the IRLink Sensor and the Power Functions IR Receiver
    <\/p>\n

    \"\"<\/a><\/p>\n


    <\/p>\n

    Those linear actuator connector barrels make for a great link to allow the drive system rotate<\/p>\n

    \"\"<\/a><\/p>\n

    Front view of DG
    <\/p>\n

    <\/a> \"\"<\/a> <\/a><\/p>\n


    <\/p>\n

    Bottom view of DG<\/p>\n

    \"\"<\/a><\/p>\n

    Future Plans:<\/strong><\/p>\n

    I have also added a HiTechnic IRLink sensor to the NXT as I plan on programming a full autonomous mode where the robot would navigate on its own.\u00a0 When running in this mode, the NXT would issue commands through the IRLink senor to the Power Functions receiver to control the drive wheels while also monitoring the Acceleration sensor.\u00a0 In addition to this, I also have a Techno-Stuff DIRPD sensor on there to aid in object detection up front. Stay tuned for more on this later…<\/p>\n


    <\/p>\n

    \"Uses<\/p>\n

    \"Uses<\/p>\n

    \"Uses<\/p>\n

    \"Uses<\/p>\n

    \"Uses
    <\/p>\n


    <\/p>\n


    <\/p>\n


    <\/p>\n

    Rate This Post: \"1\"2\"3\"4\"5 (7<\/strong> votes, average: 4.29<\/strong> out of 5)
    <\/span><\/span>Loading...<\/span><\/p>\n","protected":false},"excerpt":{"rendered":"

    Sometimes I build robots that attempt to solve real world challenges.\u00a0 Other times, robots are built based on random ideas. This robot is a case of solving a LEGO challenge – specifically, with their Technic tracks\/treads #575518.\u00a0 At no fault of theirs, these plastic tracks are slippery on many surfaces.\u00a0 Great for carpets, flat areas, dirt (if you dare) – and great for turning as well.\u00a0 However, when you try to climb with them, they … Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":4,"featured_media":1214,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[18,3,4],"tags":[22,34,21,24,11,47],"class_list":["post-1086","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-autonomous","category-legorobots","category-nxtrobots","tag-accelleration-sensor","tag-dirpd-sensor","tag-hitechnic","tag-mindsensors","tag-nxt","tag-powerfunctions","has_thumb"],"aioseo_notices":[],"jetpack_featured_media_url":"https:\/\/www.plastibots.com\/wordpress\/wp-content\/uploads\/2009\/01\/DGshowingDualStateL1.jpg","jetpack_shortlink":"https:\/\/wp.me\/pK41j-hw","jetpack_sharing_enabled":true,"post_mailing_queue_ids":[],"_links":{"self":[{"href":"https:\/\/www.plastibots.com\/index.php\/wp-json\/wp\/v2\/posts\/1086","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.plastibots.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.plastibots.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.plastibots.com\/index.php\/wp-json\/wp\/v2\/users\/4"}],"replies":[{"embeddable":true,"href":"https:\/\/www.plastibots.com\/index.php\/wp-json\/wp\/v2\/comments?post=1086"}],"version-history":[{"count":0,"href":"https:\/\/www.plastibots.com\/index.php\/wp-json\/wp\/v2\/posts\/1086\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.plastibots.com\/index.php\/wp-json\/wp\/v2\/media\/1214"}],"wp:attachment":[{"href":"https:\/\/www.plastibots.com\/index.php\/wp-json\/wp\/v2\/media?parent=1086"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.plastibots.com\/index.php\/wp-json\/wp\/v2\/categories?post=1086"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.plastibots.com\/index.php\/wp-json\/wp\/v2\/tags?post=1086"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}