Step 6: CIM Motor Drive Part2 - Application to the Longboard

The CIM motor drive was originally developed to be compact enough to fit under a longboard deck. We decided that only one bracket was sufficient to hold the motor in position. We could have fixed other side of motor, too, but they're so light that ¼" aluminum on one side was fine.

The CIM motor spins at a much higher rpm/V than the stock motor. In order to keep stock torque and top speed characteristics, we needed to gear them down- thus the need for the planetary gearboxes. The CIM motors @ 18V + the planetary + 1:1 timing belt gear ratio ~= stock motor @36V + 19:44 timing belt gear ratio in terms of rpm and torque. Note: we know that CIM motors are meant to be run on 12V and that we are running them at 18V (2 motors in series on a 36V circuit = 18V per motor). This is fine; they handle the higher voltage and rpm without any issues.

The Exkate drive wheels have a 44T gear permanently attached to them. We did the gear ratio calculations and it turned out that a 1:1 timing belt gear ratio was fine, so we bought 44T gears to attach to the planetaries. If you use a smaller gear, you'll get more torque (and thus acceleration), but I can tell you from experience that there is PLENTY of torque. A larger gear will give you a higher top speed (but less acceleration).

But why did we go with 2 motors instead of 1 bigger motor with a solid rear axle or differential? (You can buy differentials for tricycle-style bicycles that are small enough to fit.) One reason is that both would require a complete chop-and-rebuild of the rear truck in order to get them to fit in the proper place; we'd basically have to design our own truck. But besides that, there are other problems with both. A solid rear axle would mean that both rear wheels would be spinning at the same rate. This is bad for turning. When a car turns, the outer wheels have to spin faster than the inner ones. If you have a solid axle on a longboard, the outer wheels have to slip in order to make the turn. This would seriously hurt the turning radius. A differential would alleviate this problem; however, in the case of longboards, it causes a different problem. A longboard is turned by leaning in the direction you with to go, causing more force to be on the inner wheels than the outer wheels. This means that the outer wheels have less traction. With a differential, the side with less resisting force (traction) gets more torque and vice versa. This means that, in very sharp turns where the outer wheel comes off the ground, the outer wheel will get all of the power and the inner wheel will stop spinning. This is the same problem we had with 1 wheel drive, but now on either side of the board! In summary, a solid rear axle or differential were not good ideas.

So we used two motors. However, one thing we didn't foresee until it was too late was that we had created an electronic differential by wiring the motors in series. If one motor has less load than another, it will steal power from the other motor. Ideally, the two motors should be wired in parallel. However, that can't be done with CIM motors because, while 18V is fine, 36V would probably cause them to explode. The second best possible solution is to find two relatively low rpm/V (so that you don't need the planetaries), light weight, compact, 36V motors and wire them in parallel…I couldn't find any such commercial motors. The best possible solution would be to completely overhaul the power system by using two motor controllers (one for each motor),  finding motors that match our needs exactly (and don't need the planetaries), and creating a new radio scheme (because the radio receiver is integrated into the current electronics module).

Note: when I say “motor”, I mean brushed motor. We decided to go with brushed motors over brushless because of their simplicity, being cheap, and ability to wire them in series or parallel. Brushless motors are more efficient and more powerful, so if anyone wants to undertake a brushless version of this project, that would be cool! (I'm building one with in-wheel brushless hub motors, check it out here: http://www.mitrocketscience.blogspot.com / ) .

The last thing to mention is how we mounted the brackets to the trucks. A hole was drilled in the bracket plate large enough to fit the truck through. Two small two piece clamps were machined out of 2” aluminum round stock. First, we cut 1/2 inch pieces of the 2” round. Then those had a big hole drilled in the center smaller than the diameter of the trucks at the point we were going to clamp it (if these holes end up being too small, filing can fix them). Then they were notched (see pic) and holes drilled (for a #10-32 tap) perpendicular to those notches. Two clearance holes for 10-32 were drilled through the face of each (to be used to screw the bracket to). Then they were cut in half (see pics). Then the bottom sections were threaded for 10-32 and the top sections were drilled out for clearance. The end result was two, 2-piece clamps that would fit snugly onto the trucks when screwed together. After fixing them to the trucks, the two face hole locations were transferred to the brackets and drilled and tapped for 10-32. Then everything was shimmed (to get the motors straight because I can almost guarantee that the clamps won't sit perfectly straight on the trucks) and bolted (with loctite!) together. Note: a better way to do this than clamps would be to weld the 2” round disks onto the truck.

Cool build! I just started to make my own. https://youtu.be/yWeLAkTYFoY (build log)<br>I will try to make the best quality board under 400 $
<p>Hi this is a great resource! The link to the battery in the instructions does not work looking at the picture of the battery it said it was 15 c I could not find one of those do you think 20 c would work as well?</p>
<p>If it's a higher C, Then it should probably work...</p>
<p>Hi, I've added your project to the <em style="">&quot;A Collection of Homemade Electric Motorized Skateboards (That You Must Make!)</em><em style="">&quot;</em> Collection</p><p>This is the link If you are interested:</p><p><a href="https://www.instructables.com/id/A-Collection-of-Homemade-Electric-Motorized-Skateb/">https://www.instructables.com/id/A-Collection-of-Ho...</a></p>
Your style is unique compared to other people I have read stuff from.Thank you for posting when you have the opportunity, Guess I will just bookmark this page.<br> <br> <a href="http://skatedeville.com/" rel="nofollow">Longboards</a>
I PMed the author about this question, but just in case you guys have any info about it too; do you guys know if there is a dual-shaft CIM motor available?
I'm not him, but I believe that there is not a two-shaft CIM. CIMs are a very regulated type of motor, as the main market for them is to FRC teams (robotics), one of which I am a member of. <br>I know they do not allow two-shafted CIMs, therefore, there would be very little market for them. No market means no product made, so I doubt they're made. <br>There is, however, a Mini-CIM, which is 2/3 the size, and power, but at the same speed, so if you're thinking of making it two-wheel drive, that may work by mounting them back-to-back.
Do you have any new sources for the planetary gearbox? I can't find any good slim planetary gearboxes. The link in your instructable is dead.
Hey, this instructable looks really great and I'm going to attempt building a skateboard from scratch. However, while gathering the pieces I see that your link to planetary gearboxes is invalid. Do you have a link to a place where I could buy them now? <br> <br>Thanks! <br>Devix
After a bit of searching, I found this gearbox: <br> <br>http://www.andymark.com/product-p/am-0449.htm <br> <br>that should work with a CIM. <br> <br>Any clues whether or not this is the correct one? <br> <br>Thanks! <br>Devix
So I'm interested in building something like this, but using mostly electric scooter parts on a mountain board. The battery I have is hella heavy and I want to be able to carry the board around when I'm indoors on campus. I love the idea of using lighter batteries and just have this one question. The motor is running on 24V, how would I achieve that with the batteries you used, or something similar?
Being a member of a FIRST robotics team, I'm used to working with CIMs all the time. I think there may be an alternative or two if you are worried about weight. In robotics, we also use motors called Banebots or sometimes Fischer-Price motors. either one of those, combined with the right gearbox ratio, may be a lighter and cheaper option compared to the CIM. <br> <br>Nice job though!
I've started build a electric longboard based on this instructable but from scratch, making a acrylic transparent deck and without the altered electrics module because its so expensive.<br><br>I got a huge problem, how does the brake work?<br>Can't really see any pictures on any physical brake, so i've started thinking that it got to bve the motor.<br>The only way i find this possible is that the electronics module runs the motor backwards to make it brake, but that feels a little strange.<br><br>Can anyone check how the brakes are set up on any altered or other electric longboard?
And what timing belt gear?<br>If im not wrong, was it this one? <br>https://sdp-si.com/eStore/PartDetail.asp?Opener=Group&amp;PartID=5370&amp;GroupID=218
The Exkate controller features regenerative (electric) braking. You could alternatively buy a Kelly controller with regen (or one of a bunch of other brushed motor controllers), if you don't want to spend the hundreds of $ on the exkate controller.<br><br>Almost all electric (commercial) longboards use regenerative braking.<br><br>I honestly don't remember which timing belt gear I used, but it was similar to that. I suggest experimenting with gear (timing) ratios to find one you like best.<br><br>Good luck!
Thank you very much!<br>I'll read some about the kelly controllers :)
Friggin great example of what first robotics kids do after 6 weeks off builld lol
What i don't understand, is that your battery system is set up for 36V, but your motors are clearly 12V, and trust me they will burn if you run them at 36??
They are wired in series (36/2=18V), and they can handle 18V without issue.
Okay this is cool...I have all the tools including a mini metal lathe etc. I want to build from scratch (ground up) and your instructable isn't 100% detailed. For instance, could you please update some line items like #2 &quot;Two CIM motors&quot;, where, how much, part numbers, etc.? What are the part numbers for every &quot;major&quot; component like in #6 the belt gears, you just give the main site and they have a ton of gears? Thanks!
The CIM motors are the classic FIRST robotics motors. I put links in various places in the instructable to their specs. As for a place to buy them, I just googled &quot;first cim motor&quot;. Many places sell them. Ex: http://www.trossenrobotics.com/store/p/5142-FIRST-CIM-Motor.aspx <br><br>The timing belt gear ratio you use is somewhat dependent on the motor controller(s) you use. If you use the Exkate one like us, then you could try the gear ratio we used. Step 6 mentions the gears we used (44T). https://sdp-si.com/eStore/ , and look under &quot;timing belt pulleys&quot;. <br><br>Anything else?<br><br>Hope that helped.
Some updates:<br> <br>1. Make sure you make the bracket-claps better than we did. They should match the profile of the trucks. If they don't, they are prone to slipping. Also, I'd suggest using bigger and coarser thread screws for the clamp. Or just braze or weld it.<br><br>2. Make sure you use a good bottoming tap with the drive gear - planetary interface because you'll need as much thread engagement as possible to prevent the motor's torque from ripping the screws out. If worst comes to worse, JB Weld the screws in.<br>
Great instructable,but I somewhat disagree with the premise of making an electric longboard.I think longboarding is about the experience,about pushing yourself(literally) to go that extra mile.An electric longboard just takes out the fun of riding a longboard,because you're pretty much capped at the speed of the motor,and pushing isn't an option because of the weight. But that's just my opinion.
It is ideal for a person like me who has limited control of my left side due to nerve damage. I felt like a schmuck when I could no longer skate, but an electric drive board put me back on the streets.
Woah.What happened?Are you better now?
Have you ever ridden an electric longboard? It's a lot of fun, and I believe it is actually a progression towards the original goal of longboarding: surfing on land. And this board is even more so. But that is just my opinion. As for the speed (if 15mph, 20mph with gear changes, isn't fast enough), the speed of the motor is not the limit- the motor itself is. You are by no means limited to CIM motors. There are hundreds of more powerful (in terms of rpm and torque) motors out there, including much more efficient and powerful brushless motors....the brushed CIM motors are just the tip of the iceberg. With a few hundred dollars in upgrades, I know I could change its topseed to well over 30. However, you are correct about pushing; while it is possible to push this board, it really isn't pleasant.
I know a shop by the beach that rents them.Will try them out sometime! As for surfing on land,I'll have to agree with you.That's where the sport started,am i right?
Yep. Just a warning, the boards they rent might not turn well (if the stock exkate we used was any indication).
I tried it out today,you were right about it not turning well. It was pretty cool,but the longboard I rented was topped at 5mph since it was a beachside park with tons of people.
(No REPLY button??)<br><br>No sensorless.<br>Making your own sensored speed controller won't be eazy and will take mutch more time. + a more expensive motor :)<br>I don't think it need to be sensored with that power (can be wrong,, ...will see... ) :)<br><br>I measure the current of the motor to adjust the controll signal,, its not really the same as sensored control but better than nothing :)<br><br>You need more speed but I need more torque :)<br><br>For more speed you need better motors. If you use more motors you will have more torque but still the same speed. (II think you already know that) :)<br><br>No problem :) I have the same controller as him to drive my revo (http://www.traxxas.com/products/promo/5605_promo.htm)<br>Massive brushless power!!!! :D Top speed 65mph! :p
I'm not sure why the reply button disappeared.<br><br>I'm running sensored brushless on mine (not the board in this instructable). Like you said, it takes more time and more expensive motors. The reasons for using sensored control are: a. the motors are current (and therefore torque) controlled, allowing for precise acceleration control. b. no cogging because the sensors know what state the motor is in. With sensorless, you might find that you have to kick start the board. As for measuring motor current, I don't see how that could help you control the board if you're using sensorless control. Sensorless control is always voltage control, which means control via RPM and not torque. Another way of putting it is that if you slam on the throttle with a voltage controlled system, it will apply infinite (well, as much as the batteries or motor controller can handle) current until that throttle command (RPM) is reached. There is no direct control of current, so you don't have any direct control over acceleration (indirectly, you do control acceleration by slowly applying throttle so you don't burn out). Sensor vs. sensorless brushless control is a subject I strongly suggest reading up on if it interests you.<br><br>I feel &quot;better&quot; is the wrong word, especially because I custom engineered (design and fabrication) them. For more speed, I'd need a motor with one or more of the following: less turns, shorter, weaker magnets, larger diameter tires. However, I felt around 25mph was plenty, so I designed for that. <br><br>It is true that if I use more motors, and don't divide the current among the motors, then I will have more torque. <br><br>Nice. I used to have a brushless Revo, too. It was an old Gorillamaxx conversion with a Neo 8XL and BK-electronics controller: 1800W. It could hit about 55mph. I sold it because I got sick of replacing twisted Ti driveshafts and shreaded hardened steel diff gears, haha.
I use pwm control so the motor has always the same voltage,, and the same torque<br>Much better than voltage control.<br><br>Do you have pictures or videos of your other boards? :)<br>I'm really interested :)<br><br>I have steed drive shafts on it now :)<br>I don't have much time for it now...<br>But I see it on the bright side,, no more broken parts :p
Yeah. There's a link to my blog in the instructable (and from there you can link to other blogs that are amazing sources of knowledge).
If you take a total of 9S lipo battery's you have 33.3V and not 36V
You didn't read everything. At full charge, a lipo cell is at 4.2V. At full discharge, it's at about 3V per cell (depending on your LVD or motor controller). Therefore, at max charge, 9S is 4.2*9 = 37.8V. At full discharge, 9S is 3*9 = 27V. Please actually read up on batteries before commenting.
The original batteries are 13,8V when totally charged. 13,8*3 = 41,4V. When using 10S lipo,, at max charge you have 4,2*10= 42V So you do have a little more power and still 30V when full discharged. I use 6 5SLipo's,, 18,5V 5200mah so you have with 10S3P ~37V and 15,8A (for larger runtimes) Its only a suggestion. Its a nice instructable. Do you have a video of it when driving?
We didn't go with 10S because we were worried about over-volting the electronics module and frying it...but that's a good point about the lead acids. Still, we erred on the side of caution, and there is no noticeable speed loss, probably due to the CIM motors. That's a lot of battery. 6.6Ah is plenty for this boards purposes (getting around campus). The other board I'm building will have a 12S setup with either 10Ah or 15Ah. For vids, see the link in step 10.
I'm using 1 big 1KW motor. (35A) So I need the 15Ah :) nice vids You already now the top speed? :)
Dang, what's you're top speed and acceleration like? Our top speed is around 15mph. The other one I'm building will be using four 500W hub motors and it should have a top speed of just under 30.
Its not finished jet :)<br>I'm building my own speed controller for it.<br>And I also use a mountainboard wit air tires<br>Top speed will be (at least) 40 Km/h (25 mph)<br><br>If you go faster it becomes a little dangerous...<br>But it's possible :p<br><br>I'll post a video when finished and tested :)<br><br><br>4 500W motors? I think you can reach the 40 mph with that :p<br>See this link: http://www.hobbycity.com/hobbycity/forum/forum_posts.asp?TID=12064<br><br>The board with 4 motors is so awesome!! :p
Are you using sensored control? <br><br>For my board, I calculated the top speed to be just under 30mph. My wheels are 4&quot; in diameter compared to the 8&quot; for air tires, so for a given power rating, my top speed will be lower (however, my acceleration can be quicker). <br><br>THAT IS AWESOME! Haha, wow. Thanks for sharing the link! He's using sensor-less control, so he gets cogging at start up. I like his design though. Very simple and relatively easy to implement. My hub motor design takes a lot of machining and wouldn't be able to handle the kind of shock loads a mountainboard experiences. <br>
Oh, and after reading more of the thread, it turns out he switched to sensored control (by just adding sensors to sensorless motors...very easy to do) and his performance improved greatly.
I bought one from Exkate when they were still small, and I found out how expensive they were. See I bought it from my local Spencers for about $39 because it was their last one in stock and had it for years. So it got cheaper but the battery was existed from sitting so long unused. Then I made the mistake of returning it it was only after I found how much it was worth. The only thing I didn't (don't) like about it (them) is that it uses a radio transmitter, I'd prefer wired because there is no chance of someone being on the same frequency. But one question: Doesn't the belt and reduction wheel look a little to close to the ground for turning?
The new ones use digital link up, which means it's physically impossible for someone to be on the same frequency...it's very reassuring to know the board won't randomly fly out from under me. <br><br>Nope. They don't interfere with the ground when turning. The motor bracket will scrape sometimes because of the 1/2&quot; ground clearance, but it protects the gear and belt.
lols they are frc cim motors, but hey you can buy them online anyway and with pre mounted planetary gaer reductions too
Yes, I know you can, I never denied that. But this one is the most compact design I've seen.
im sorry if i came off in that manner, i was meerly stating something
thats rad mannn smoke a duby on dat sunbitch i like it alot
With all the materials, what the cost of this project?
See step 9

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Bio: MIT Undergraduate
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