Thread: Electrathon - A Different Kind of "Hotrod"

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Not only is a least one person accessing this thread.... Your build was enough of an incentive to get me started in the sport!

I am a little overwhelmed getting my mind wrapped around all the wheel options. Back on post #55 of this thread you mentioned you made a custom setup based on mountain bike hubs which acept disk rotors and double wall alloy rims.

I was wondering if you could share more info about the brand of hubs and rims you are using on your wheels.

Thanks
David

Hi David, and welcome to Electrathon. Yes, I am happy to help anyone get going in this sport. The wheels that I currently use are a hybrid combination of components that have proven themselves to be pretty reliable. I have experimented with different pieces over the years and the following is what my combination has evolved into...

I start with a 20 inch Weinmann DM30 double wall alloy rim with 36 spoke holes. I usually just go on Amazon and search for the best price and availability. I'm sure that there are other rims that are good, too, but I've had pretty good luck with these and they are reasonably priced, so I've stuck with them.

Next, I look for a 36-hole hub that has sealed bearings and the six-hole flange for mounting the brake disc. I have found them that accommodate 20mm and 15mm thru-axles. The 20mm ones can be used on a 1/2 inch diameter spindle with bronze bushings available at ACE Hardware (3/4" o.d. with 1/2" hole). The 15mm ones can be used on 9/16" diameter spindles. Right now I am using the 15mm hubs on the cars that I build, but I have used both in the past and both are equally good. I don't have a brand name on these and they are unmarked; I will try to find the e-mail address of the supplier and post it later. Anyway, they are just some hubs I found on Ebay or Amazon and not horribly expensive.

The final component is the spokes. Conventional bicycle wheels use 14 gauge spokes; they are good for one race. At the second race they start breaking in the corners. I once had a front wheel that broke so many spokes it started wobbling visibly. I got black-flagged while running in second place with less than 4 minutes to go. When I got to the pits I counted 13 broken spokes on that wheel! After that I bought 12 gauge spokes and re-laced all my wheels with them. Now I usually break one or two spokes per race meet and I've not had any major problems. I would use 10 gauge spokes if I could, but nobody makes them in the correct length (7 1/4 inch or 184mm). Also, I check spoke tension and wheel trueness after every race. Our events here in Florida usually are comprised of two 1-hour races; I check spoke tension and wheel trueness between races - it's that important.

In order to put all these things together you will have to drill out the spoke holes in the hubs to 1/8 inch and the nipple holes in the rims to 3/16 inch. Also, check the valve stem hole in the rim to make sure it fits the stem on whatever brand of inner tubes you are using. If you need help on learning to lace rims, there are several videos on Youtube. After the first few you'll get faster at it.

Where are you located? Where will you be racing?

David - Here is a link to the hubs:
http://www.amazon.com/Wheel-Master-T...icycle+hub+36h

and the spokes:
Amazon.com : SPOKES ACTION 12G 184MM 7-1/4 72PC SILVER : Bike Spokes And Accessories : Sports & Outdoors

That's the only place I've found the spokes. There are enough in a package to do two wheels. They aren't always in stock, so buy enough so you'll have spares to replace broken ones.

Just ordered 5 rims, 3 front hubs, 2 rear hubs, and enough spokes for 6 wheels.

I think I will tackle rotor disks and brakes next. There seems to be a lot of good information floating around.

There are a bunch of brake options to choose from, so as usual, I try to pick something that fits the pocketbook and still works good. MTB makes a good quality disc brake, but they are difficult to adjust. When I got them so they were effective enough, they created some slight drag on the rotors (a definite no-no in Electrathon where friction is a detriment); when I adjusted out all the drag they didn't work to my (or the tech inspector's) satisfaction. For the last few cars I've built I used Bengal brakes. They are price comparable to the MTBs. They have a different leverage ratio built into them, so they run without drag and still stop the car efficiently. I buy them on Ebay. If you buy them in pairs it saves a few dollars.

What did you get for rear hubs? I usually buy a 48 spoke BMX wheel for the rear with the 14mm axle and the threads for the screw-on sprocket cassette. I run them until they break a couple of spokes and then re-lace them with the 12 gauge spokes. I get the sprocket hub from Rodney Schreck in Miami. It's made to accept a standard go-kart sprocket and I use an aluminum sprocket for #40 chain.

Thanks Jim,

Sorry it looks like the moderator ate my reply from yesterday. Maybe because I am new and I used a link to an external site

In summary... I am from Western Wisconsin, along the Mississippi river. Our state organization holds four events each spring which lean heavily towards high school students. That should give me 6 months to get something going

For a rear hub, I went with a Wheel Master Rear Hub Freewheel - 36H Bolt-on Black 135mm O.L.D. 6/7 . It was pretty cheap, enabled me to use the same rims and spokes as the front wheels. If they show sign of failure, I am not out much and can reuse the rims as spare fronts. It seems to have standard threading for a bicycle freewheel.

I was planning on not thinking too much about the drive-train except for size and weight constraints until after the frame is nearly done. Otherwise I get too many variables floating around. Right now my primary goal is to establish the wheel geometry so I can use the front spindles and rear dropouts as the starting point for the frame.

I guess I should get the brakes pretty soon as they will have a significant effect on how the front wheel mounts are designed.

David

Sounds like you're on the right track. For when you're ready, here is the link to the rear sprockets I use:
Racing Sprockets for Larger Chain Sizes
I get my motor sprockets, chain, and master links from Robot Marketplace.

A lot of teams like to use #35 chain, but I have had some bad experiences with it. If you have any frame flex or if the motor or rear wheel get knocked just a little out of alignment, the chain pops off. I switched to #40 chain about 6 years ago and virtually ended my chain related failures. It has to be seriously out of alignment to come off.

Just a quick update.

Most of this week was spent on the basics. I tried to start each day in the shop by spending 10-15 minutes per day practicing welding beads on 20 Gauge sheet metal. I figure that practice will come in handy when I start welding the .060 round tubing I intend to use for the frame. Next I practiced notching 6 inch segments of the 3/4 and 1 inch round tubing. When I feel more confident in my welding, I'll use the notched tube segments for practice and then destructively test them.

Inside I tried to spend an hour or two learning solidworks. Not sure if that is strictly necessary, but I would like to eventually be able to run some analysis on frame designs.

The wheel components arrived today. Going to start assembling them this weekend.

Next weeks project looks to be a continuation of the basics while designing and fabricating a prototype of the steering system. I have worked on and raced bikes of various sorts, but have never really looked at two steering systems.

If you have looked at the wheel lacing videos on Youtube, you know they recommend weaving the spokes. You won't be able to do that with 12 gauge spokes without bending them like pretzels, so don't bother. After your wheels are laced and trued, use small zip-ties to tie the spokes together where they cross. This helps strengthen the wheels and also keeps any broken spokes from whipping around and getting tangled where they shouldn't.

You haven't said, but I assume you are building a cycle-car design (two wheels in front, one in the rear). If so, study some go-kart steering (also look at pics in this thread). It's simple and direct and is basically what most of us use. You can go high-tech and buy a rack & pinion unit, but they really have no competitive advantage so, for me, it's hard to justify spending the money.

I am reverse engineering your design from this thread. I like your functional approach. Nothing is more complicated than it needs to be. You provided enough information that I am not totally lost on my first build.... While leaving enough off that it does not feel like a paint by numbers project.

I went with a cycle-car design. I figured it was more common and well documented. I'll start experimenting more on my next build.

I spent last night making cardboard mock ups of various of various steering knuckle designs (starting with yours on this thread) to get a better feel for how steering geometry affects the wheel as it moves though full right, straight, and full left turn.

Do you have a favorite online bearing vendor? I have looked around locally and none of the hardware stores seems to have much selection so I will have to go online. Interestingly, a local Custom Fab and Welding Shop will sell me steel at cost for this project to help kick off a local team.

David

Yeah, I like to keep things simple. It makes maintenance faster and easier and makes the racecar more reliable. 50+ years in racing has taught me that reliability and preparedness are the two most important components in any racecar. Let me know if you get stumped anyplace. I can measure one of my cars to get dimensions and you can change or modify to suit your application if needed.

I prefer the cycle car configuration. I race against a couple of tricycle cars and they have handling problems on the tight courses. Also, in my 12 years of Electrathon I have seen 4 rollovers - 3 of them were tricycle cars.

Bearings for what? If you are referring to the rod ends I use in my steering (tie rods), I get them from Speedway Motors online. ACE Hardware also has them, but they are much cheaper from Speedway.

That's good, a vendor who will help you out. I got the local Auto Parts store to sell me my batteries at a discount price, but that's about it.

I was thinking about bearings in general. Something like the booklet my steel vendor gave me. ( http://www.centralsteel.com/images/s...odguidepub.pdf ) I spend more hours than I care to admit pouring over that booklet and various Wikipedia articles on steel.

Specifically I am looking for bearing for between the kingpin boss and steering knuckle. It appears that you used nylon for the top and a flat bearing for the bottom.

In the end I went with 3/4 and 1 inch OD tubing with a .060 wall thickness. It lined up nicely with your recommendation for using conduit but the wall is slightly thinker... and more forgiving for a new welder.

My current back of the mind issue is battery location. The three general location that seem common are pods beside the drive, behind the drivers seat, and between the driver legs.

-- Pods appear to be very stable by proving ballast low and wide. But the pods add frontal area.

-- Behind the seat enables a narrow profile. But increases the length of the vehicle while shifting the center of gravity towards the single rear wheel.

-- Between the legs seems to provide better weight distribution and stability by provide a heavy ballast low and between the front pair of wheels. Aerodynamically, batteries + legs fit in the 21 inch frame. It also helps keep the wheelbase nice and short.... But I am not sure how happy I am to have 70 lbs of lead acid batteries between my legs

thanks again.

David

I finally started building last week! Got two front wheels put together. The first took seven hours and the second took about an hour. Wheel building with short 12 gauge spokes take a bit of planning and finesses I hope to do two more this evening; the rear and a spare front. Jim's guidance on drilling out the rim and hub holes worked perfectly.

Later this week I hope to rig up a truing stand from an old set of BMX forks. How high do you tension the spokes? In my limited experience with spokes on a standard bicycle wheel I would just 'pluck' the spokes until they sounded and felt similar to the rest of the spokes on the wheel.

With these short and thick spokes, it feels like the nipples will pull though the rims before I get a nice tone

Today's primary goals will be picking out the tires, tubes, brakes, and brake disks. If I recall, hookworms are the preferred tire and you suggested Bengal brakes because they were inexpensive while being good enough.

With regard to bearings. I was thinking about bearings in general. Kind of a one stop shop. Specifically, I was looking for bearings to go between the steering boss and steering knuckle. In my mind, I am thinking something like the upper and lower headset bearings on a bike... but that might be over kill in this application.

Thanks.

David

Sounds like you're off to a good start. The 12 gauge spokes don't "ring" like the smaller ones, so sound probably isn't a good way to gauge their tightness. I use an ordinary screw driver to tighten them when I am lacing a new wheel. I get them so they are really snug, but not so tight that the nipples are hard to turn. I try to get them all as close to the same as I can by "feel". If you have one or two spokes that are overly tight surrounded by others that aren't tight enough, the tight ones will break. One thing to note, a new wheel will stretch the spokes the first time you run it, so be sure to tighten spokes and true the wheel after the very first race (or extended practice session).

Yes, definitely overkill for these light vehicles. I won't go into detail about how I build the spindles because it's covered earlier in this thread, but I don't bother with bearings. I just use a washer at the bottom between the kingpin boss and steering knuckle and keep everything well lubricated. A little slop in the spindles/kingpins is tolerable. When they wear to the point where I think they're too loose I get bronze bushings from ACE Hardware, trim them to length, and bore the spindles out to accept them. It's tedious, but easier than building new spindles.

What I found works pretty well for these stiff spokes is to grab the parallel set of spokes and squeeze really hard. An example is at "How to True a Bicycle Wheel - YouTube by Donswoodshop" starting about minute 10. ( Sorry, I can't add link directly or my posts seem to get stuck in moderators queue)

I started by tightening the nipple until I could only see on thread on each spoke. Then I went around the wheel squeezing each set of parallel spokes follow by going around the wheel tightening each spoke 1/2 turn.

Repeat until spokes are evenly tightened. Whenever I hit a spoke that felt overly tight next to a loose neighbor, I loosened each spoke on the wheel 1 full turn and went around the wheel squeezing and tightening. After a couple of iteration I had some pretty evenly tightened wheel.

My biggest challenge was that the hub was rotated slightly within the wheel. As a result a pair of spoke pulling in one direction would be tight while the next pair pulling in the other direction would be loose.

Hope this helps someone else learning to build their first vehicle with spoked wheels.

David