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Tin Lizzie conversion

I have a vintage tin Lizzie (1/4 scale model T Ford) l want to convert to electric...l need motor, brake, accelerator, and batteries, l want to go 15-20 mph, it currently has a 3hp Briggs and Stratton with a transmission connected by a belt...control is a lever which tensions the belt and a bar which contacts the rear tires for the brake....all connected by a system of levers, shafts and linkage which is worn out....16" tires...thanks....Tom

Hi Tom, wow that is quite a machine you have there.

A 1000 Watt electric motor will have enough power for a 20 MPH top speed, and a 750 Watt electric motor will have enough power for a 15 MPH top speed. The electrical part of this build will be the easy part though and we can figure that out after we figure out the gear ratio and sprockets needed to achieve the top speed that you are aiming for.

I imagine from looking at the gear box on the car that the top speed as it is built right now is fairly slow, like in the 5 to 10 miles per hour range. If the car was built for a 15 to 20 miles per hour top speed then the gear box would not be needed and the drive belt could run directly to the rear axle without going through a gear box. However maybe the gear box does not reduce the gear ratio that much and can be left in place for the conversion. I can figure all of this out and come up with a drivetrain plan by asking a few simple questions:

  • How many times does the gear box's belt pulley fully rotate to make the wheel fully rotate one time?
  • What is the diameter of the tires?
Hi...thanks for the prompt reply... gearbox rotates about 11¹/2 times to one wheel rotation...tire diameter is 16"...our goal with this project is a relatively safe and reliable ride for the speed is not an issue...5-10mph is just will be used in mildly hilly country mostly dirt and gravel roads...would like to carry one adult and one kid..maybe about 200lbs...steering is adequate as is...we would like it to go and stop like a golf cart....thanks!!

If my math is correct and 11¹/2 = 5.5 then the gearbox has a 5.5:1 (5.5 to 1) gear ratio. I ran some gear ratio calculations using a 5.5:1 ratio gearbox and found that using a 2500 RPM motor with 11 tooth sprocket and a 24 tooth sprocket on the gearbox the top speed would be 9.95 mph. Here is the gear ratio calculation.

Here is the calculation for a 4.97 mph top speed using a 48 tooth gearbox sprocket.

From looking at the photos I assume that you want to keep the gearbox on the car because it is one of the best mechanical features that the car has. However if you want to remove the gearbox and run a chain directly from the motor to the rear axle then here is a gear ratio calculation for that.

An 89 tooth sprocket for #25 chain is the largest one that is available off the shelf. You can see with this setup that the top speed is 14.76 mph which is faster than you mentioned wanting the car to go.

If you gear the car for a 5 mph top speed then a 250 Watt motor would work, and if you gear it for a 10 MPH top speed then a 500 Watt motor would work. These motor sizes are for use on mostly flat ground, if the car needs to go up steep grades then the motor size should be increased for that.

Once you figure out which parts would be best to use for this project then we can make a kit out of the parts if you would like. Our kits are pre-wired for easy plug and play installation.

Please let us know if you have any questions.

Hi...once again thank you for the prompt reply... hopefully l am understanding correctly... leaving the existing gearbox makes sense....l think the 500 watt motor and about 10 mph top speed will be fine...l do have a question about brakes....the existing system is a lever connected to a shaft which bears on the tires...l would like to upgrade the motor self braking or would l need to install a disc brake... thanks...Tom

That brake which bears on the tires is known as a scrub brake which are fairly ineffective and puts a lot of wear on the tires. Upgrading would be a good idea, especially if the car is geared to go 10 miles per hour.

The motor will slow the car down a little when the accelerator is let off of, however it will not act as a brake so an mechanical brake will need to be used along with it in order to get the car to stop.

I think the best solution for a brake might be to use go kart brake parts, as these are designed to go onto an axle and for the weight and speed that your car has. Although we do not carry go kart brakes they can be easily found online by searching for "go kart brakes". I just performed this search and found many different styles including drum, disk, and band brakes. Most of them are for a 1" axle and I am not sure what the diameter of the axle is on your car, however there are most like adapters or brakes for other size axles as well. have been extremely prompt and helpful...l will deal with brakes following your instructions...the car does indeed have one inch axles...l am ready for you to put together an electric kit for the car...the 500 watt motor and about 10mph....let me know price and availability and I'm ready to order....thanks...Tom
That is great new that it has a one inch axle since most go kart brakes are for that size.

Before I make the kit we need to decide what size batteries you would like that car to have. It could have small 9Ah batteries which would give it around a 20 minute ride time, 15Ah batteries for a 35 minute ride time, 22Ah for a 45 minute ride time, 35Ah for a 1-1/2 hour ride time, 50Ah for a 2 hour ride time, etc. These ride time estimates are for continuous full throttle riding on flat ground. Riding at less than full throttle will provide longer ride times, and riding in hilly areas will provide shorter ride times.

Do you have any idea what size batteries you would like the kit to have?

Also regarding the 24 tooth chain sprocket for the gear box. Do you know what the diameter of the shaft is on the gear box that the sprocket goes onto?

Ok..... available space with no modifications is 20" from back of body to rear bumper...width inside of frame rail to rail is 15"...shaft on gearbox is 5/8"...l would like to use the largest batteries that will fit... in the available space...also note the the gearbox"floats" on the axle shaft...the existing"clutch" consists of a lever that tensions the belt to drive the gearbox shaft from the idea is to eliminate this system with your electric kit...
Hi again.... just wanted to make an observation...after reviewing our conversation from the last few days l appreciate how thorough you have been with your explanation, knowledge of your subject matter and your patience . I am a grandpa with a lifetime of auto repair and restoration experience and a retired high school auto shop teacher. The planning stages of any project are the most important part of a successful finish. I must say l am impressed with your planning and communication skills...looking forward to the execution as the planning is nearing completion... thanks...Tom
Hi Tom, thanks for the positive feedback regarding my replies. If I had known that you were a master mechanic I probably would have explained less details, however I am glad to explain these things here on this forum so other people who are just starting out with mechanics can learn from them.

We have a 24 tooth sprocket for a 5/8" shaft so that part of the build is taken care of. Regarding fitting the largest size batteries that will fit in back of the car, that will take a little figuring because the motor will also be back there taking up space. It might be best if you remove the gas engine and mock up where the motor and batteries will go to see how much room there is for the batteries. The 24 Volt motor will require two 12V batteries. I will post the footprint size of the 24V 500W motor and our larger size batteries below to help with this:

24 Volt 500 Watt motor with mounting plate: 4-1/4" x 6-1/4" footprint

12V 15Ah batteries: 6" x 3-7/8" footprint per battery
12V 22Ah batteries: 7-1/8"  x 3" footprint per battery
12V 26Ah batteries: 6-5/8" x 6-7/8" footprint per battery
12V 35Ah batteries: 7-5/8" x 5-1/8" footprint per battery
12V 50Ah batteries: 7-3/4" long x 6-1/2" footprint per battery
12V 75Ah batteries: 10-1/4" x 6-5/8" footprint per battery

 I do not want to recommend a battery size that will not fit, so I would like to leave the battery size decision up to you. After you figure out what size batteries will fit in back of the car then please let me know and I will go ahead and make the kit.

Please let me know if you have any questions.

Hi...thanks again..l think the 50Ah batteries will fit nicely in the available space...just a couple more questions... does your controller come in pedal form....and l did a little research on a brake setup but was not able to find a complete kit from pedal to disc... otherwise l think we are ready to put something together...thanks...Tom
Here is my attempt at technology...hope this helps!
Thanks for attaching the photo, it looks like you have plenty of room back there for the batteries.

You might want to call or email one of the go kart part stores to see if they can put together a complete brake kit for you.

Our controllers works in conjunction with a separate foot throttle. We have three different types of foot throttles. Here is a photo of them.

The THR-89 is the largest and best quality foot throttle of them all. It bolts directly onto any flat surface. The THR-90 also bolts onto a flat surface however it does not have as smooth of a pedal feel as the THR-89 so it is not as easy to use, however it is the most compact one that we have. The THR-91 is an all metal throttle that is high quality with a smooth pedal response, it requires a rectangular opening to be cut into the floor it is mounted to and it sits flush with the floor so it has the lowest profile of all of our foot throttles. THR-89 is the one I recommend if it looks like it will work for you.

The kit I can make for your project will include a motor, sprockets, chain, controller, foot throttle, power switch, batteries, battery charger, and battery charger port. We pre-assemble all of these parts in our shop with matching and labeled connectors so they will all plug together right out of the box.

I pretty much know all of the parts to include with the kit except for the throttle. Do you have a preference as to which throttle you would like to use?

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