Razor dune buggy- need advice on safety after modifications.

[Jtroy]

Hello DIY!

First time posting, but I have been browsing the forums for over a year.

I have already modified a razor drifter with 800w motor and 36v conversion for my 8yo daughter. She loved but I got tired of how noisy it was and how fast it burned through tires. I put rubber wheels on it, but it changed the driving style so much that she didn’t enjoy it as much, she was also getting bored of the 18mph top speed.

So I wanted to try something different and have been working on reviving a basket case of razor dune buggy that I got cheap after getting inspired by the other projects on the forum. I used the readily available 48v brushless motor and controllers off Amazon. I also upgraded the front and rear wheels with 9” and 10” wheels respectively.

After months of tinkering and modifying,
I finally got it together and the test dive when a little too well. The 3 speed controller resulted in top speeds of 20, 25 and 30 mph. The thing is scary fast, but she loves it and actually handled it very well. But now I’m worried about it rolling over.

Does anyone have any suggestions on if a roll cage would be worth wild? I was considering a hoop behind the seat, or a couple hoops coming from front to back.
Any advice or suggestions would be appreciated.

ps. I will be posting final assembly pics once I possibly add the roll cage and get it painted.

 

[Denny]

When designing a proper cage there are many things to consider. The age of the child, how much is she going to grow and can you teach her not to panic in a rollover and use the cage properly.
First let’s consider design. Set your daughter in the kart with her feet on the pedals. Now draw an imaginary line from 3” above the highest part of the top of her helmet to 3” above the top of her feet. Got it? Good. That is the minimum height that the cage can be. At least for now. Now you have to figure she is going to grow. How much? You have to make an educated guess. How tall are you? How tall is your wife? Pick the tallest person and set them in the kart with the helmet on the same way and take your measurements again the same way. Now you have your new measurements for how tall the cage must be in the front and the back. How wide is the kart? That is how wide the main hoop, mid hoop and front hoop must be. Now you can design from there. Remember a triangle is the strongest geometric shape. The main hoop should be even with her shoulders straight up but behind her head at the top. The center hoop should be about 14” from that. The front hoop should be forward of her feet at the furthest riding position. Now at the corners of the hoops run a bar to connect the hoops at the corners. On both sides. Next you will want to run a bar on each side from the rear of the top of the main hoop down to the frame on the back of kart. Now on the main hoop And mid hoop again in the middle you will want to run a bar from left to right. Connect all hoops at the corners with bars.
Now where the horizontal bars are on your main and mid hoops are make an x with more bars to the bottom of the opposite bars. Now I have made the assumption you already have a high back bucket seat installed. You will also need to install at least a 5 point harness to keep her in it.
Now the fun part! How to safely use the cage. You must teach her in the event of a roll over she is to let go of the steering wheel and grab her seat belts at the shoulders. That keeps her from wanting to put her hands out to try to stop the vehicle from rolling over and breaking her little arms off. I hope you understand all I have wrote. Good luck!

 

[madprofessor]

Jtroy, that's the best description of a properly safe cage I've ever read, you can't go wrong following it completely. Just don't forget that you have to crawl in/out of it. Post pics of it before you paint it, maybe just in primer at the most. Denny or others may want to advise a cross brace or something to add before final paint. Kudos for using your head and making a cage.

 

[Denny]

Wow, I did not realize that kart was that small. She has almost outgrown that kart now. Honestly I would look for or make a bigger frame. I’m just thinking of the kid’s safety. I would rather her be thrown free, than stay with the kart and break off some limb. Just my opinion.

 

[Jtroy]

That’s kind of where I am at with it as well… I didn’t want something big, it was just suppose to be something she could tool around on, spin the tires, and have some fun. But now I’m not sure I can actually make it safe at the current performance level. It’s my fault for completely over building it. A shame because it is a total blast to ride. Maybe I just de-tune/put a governor on it.

As for the size… i was also planning on my younger son using it when he was ready, and the plan was that she would drive it for another year or so before I go her something else. So I didn’t want to completely abandon it if I can make it work.

 

[madprofessor]

You can make it work for both the younger and the growing-older if 2 karts are too much of a stretch. Stretch is the word, stretch out the cage. A cage must not be limited to the size of the kart it's going on, but rather by how safe you want to be. Kids? Maximum safe!
A 3' wide kart does not mean you can only have a 3' wide cage. You can stretch out the size of the cage to be a rolling circus "rollerdrome of daring" if you want to, and just weld it to the existing frame. 3' wide kart, 5' wide cage may look funny to some, may look cool and unique to others. All that really matters is that the kids don't get appendages broken off in a rollover, a bigger cage may address some of that. Then there's also the factor of widening the wheelbase with a longer rear axle and more width between the front spindles, a preventative measure to reduce the risk of a rollover, but the risk will always be there.
But then, Denny said..............

Honestly I would look for or make a bigger frame.

You did allude to another kart when she outgrows this one. Maybe safe this one off with outriggers and an oversized "ball" of a cage, and get her a kart that will hold you just as well if you decide to ride it.

 

[panchothedog]

You say you don't want something big. Frankly Sir that thing looks like a death trap at 30 mph, heck even at 20 mph. It is too short, narrow, and literally no protection. BE responsible and put your children in something larger with a complete roll cage, seat belts, and a helmet. I am not trying to come off too hard ,I am speaking from years of experience karting with my grandkids. I started the youngest at age 5, he is now 18. Youngest presently is 8. I own 5 karts and every one of them have cages, belts, or complete harnesses.
Children are too precious. Look at that picture of your daughter sitting in that thing. If she were to hit something solid at 15 to 20 mph she wouldn't stand a chance of not being injured. Again get something bigger or get out of karting.

 

[Jtroy]

You say you don't want something big. Frankly Sir that thing looks like a death trap at 30 mph, heck even at 20 mph. It is too short, narrow, and literally no protection. BE responsible and put your children in something larger with a complete roll cage, seat belts, and a helmet. I am not trying to come off too hard ,I am speaking from years of experience karting with my grandkids. I started the youngest at age 5, he is now 18. Youngest presently is 8. I own 5 karts and every one of them have cages, belts, or complete harnesses.
Children are too precious. Look at that picture of your daughter sitting in that thing. If she were to hit something solid at 15 to 20 mph she wouldn't stand a chance of not being injured. Again get something bigger or get out of karting.

Those were my thoughts exactly,
Which is why I was looking to see if anyone had ideas on ways to make safer. This was my second time modifying a little cart cart like this, and I surely wasn’t expecting this kind of speed increase. I’m goal was to make something a little fast with more torque.

For now, I’m going to see if I can de-tune/govern it down to near the stock speed of 13-15mph. And if not, it will get put away until I can find a bigger frame.

 

[madprofessor]

de-tune/govern it down to near the stock speed of 13-15mph

Never been really sure what folks mean by "de-tune", but this would do what I think is both de-tuning and governing down..............
Throttle limiting. The most basic thing there is in making little kids safer around locomotion machines. Running a throttle stop screw further in, adding pedal stops to the frame, anything that prevents the motor from getting too much fuel for safety. That would "de-tune" the motor insofar as preventing sudden violent lurches forward, and of course would "govern down" the top speed of the kart.
EDIT: Oops. Kept saying fuel as though it were a gas engine. It's electric of course, but same method applies.

 

[Jtroy]

I plan to achieve this with a couple changes.
1. locking the motor controller in the slow setting. The current top speed in the slow setting is 18mph, it’s 25 in the medium, and 30 in the fast.
2. this kart has a jack shaft, so I can change a couple gears to further reduce the speed. It currently has two 32 tooth and two 14 tooth gears… I can easily change the 14 teeth gears out for 11,12, or 13 teeth gears which should produce the desired result.

so, by fiddling with the gearing and the the controller speed settings, I should be able to get it into the “safe” range.
Here are couple gear/speed calculations. By changing the 14 tooth gears to 12, I get almost a 30% reduction in speed. And this doesn’t account for putting the controller in the slow setting. I would expect it to now be firmly in the teens speed wise with more torque.

if that doesn’t work, or it’s still not safe, I’ll just mothball it until I find a different frame.

 

[madprofessor]

So the "neck-snapping" acceleration we always enjoy isn't too much for the kid, just need to reduce top speed? That makes it simple, speed/ratio calculation simple like you've already done. Question: Have you considered using a sprocket hub on the axle, so that split sprockets of various tooth counts can be inexpensively swapped out in 5 minutes flat without R&R of anything on the axle?
Unihub - Sprocket Hub | AZ2556 | Azusa 2556 | BMI Karts And Parts
#35 Split Sprocket | 6335** | BMI Karts And Parts

 

[Jtroy]

So the "neck-snapping" acceleration we always enjoy isn't too much for the kid, just need to reduce top speed? That makes it simple, speed/ratio calculation simple like you've already done. Question: Have you considered using a sprocket hub on the axle, so that split sprockets of various tooth counts can be inexpensively swapped out in 5 minutes flat without R&R of anything on the axle?
Unihub - Sprocket Hub | AZ2556 | Azusa 2556 | BMI Karts And Parts
#35 Split Sprocket | 6335** | BMI Karts And Parts

I’m not really concerned about excessive acceleration.There isn’t neck snapping acceleration on the low setting which already maxes out at 18mph, so I think it will only take a 1-2 tooth reduction to actually reduce the top speed to the desired level, and that would produce a proportional increase in torque which given my initial test run should be safely in the fun range. Now, if I fully geared it down as in the example about in the highest setting, or even went further with 11tooth gears, then it might be more of a concern.

As for the sprocket hub, I had considered it but my initial plan was to maintain the stock appearance and chain guards. And due to the physical constraints of the chassis with the center mounted sprocket you can’t really fit in much bigger sprockets before it would contact the frame. I think that is likely why the initial design used a jack shaft. It also increase ground clearance.

 

[panchothedog]

So glad to hear your response. I'm the way you describe slowing the kart down you clearly are an intelligent individual with a good mechanical understanding of how things work. You clearly have the knowledge to build your children some good, fast, and safe little cars. Have fun DAD. It's a blast watching them grow and get better at it.